diff --git a/.gitattributes b/.gitattributes
new file mode 100644
index 000000000..dfdb8b771
--- /dev/null
+++ b/.gitattributes
@@ -0,0 +1 @@
+*.sh text eol=lf
diff --git a/.github/opam/custom/repo b/.github/opam/custom/repo
deleted file mode 100644
index 013b84db6..000000000
--- a/.github/opam/custom/repo
+++ /dev/null
@@ -1 +0,0 @@
-opam-version: "2.0"
diff --git a/.github/opam/ocaml-variants.opam.unix b/.github/opam/ocaml-variants.opam.unix
deleted file mode 100644
index 2de3f476e..000000000
--- a/.github/opam/ocaml-variants.opam.unix
+++ /dev/null
@@ -1,107 +0,0 @@
-opam-version: "2.0"
-synopsis: "Custom compiler __OCAML_COMPILER_FULL_VERSION__"
-maintainer: "platform@lists.ocaml.org"
-authors: [
-  "Xavier Leroy"
-  "Damien Doligez"
-  "Alain Frisch"
-  "Jacques Garrigue"
-  "Didier Rémy"
-  "Jérôme Vouillon"
-]
-license: "LGPL-2.1-or-later WITH OCaml-LGPL-linking-exception"
-homepage: "https://ocaml.org"
-bug-reports: "https://github.com/ocaml/opam-repository/issues"
-depends: [
-  "ocaml" {= "__OCAML_OPAM_PACKAGE_VERSION__" & post}
-  "base-unix" {post}
-  "base-bigarray" {post}
-  "base-threads" {post}
-  "base-domains" {post}
-  "base-nnp" {post}
-  "ocaml-option-bytecode-only" {arch != "arm64" & arch != "x86_64"}
-  "ocaml-beta" {opam-version < "2.1.0"}
-]
-depopts: [
-  "ocaml-option-32bit"
-  "ocaml-option-afl"
-  "ocaml-option-bytecode-only"
-  "ocaml-option-no-flat-float-array"
-  "ocaml-option-flambda"
-  "ocaml-option-fp"
-  "ocaml-option-musl"
-  "ocaml-option-leak-sanitizer"
-  "ocaml-option-address-sanitizer"
-  "ocaml-option-static"
-]
-conflict-class: "ocaml-core-compiler"
-flags: [compiler avoid-version]
-setenv: CAML_LD_LIBRARY_PATH = "%{lib}%/stublibs"
-build: [
-  [
-    "./configure"
-    "--prefix=%{prefix}%"
-    "--docdir=%{doc}%/ocaml"
-    "-C"
-    "--with-afl" {ocaml-option-afl:installed}
-    "--disable-native-compiler" {ocaml-option-bytecode-only:installed}
-    "--disable-flat-float-array" {ocaml-option-no-flat-float-array:installed}
-    "--enable-flambda" {ocaml-option-flambda:installed}
-    "--enable-frame-pointers" {ocaml-option-fp:installed}
-    "CC=cc"
-      {!ocaml-option-32bit:installed & !ocaml-option-musl:installed &
-       (os = "openbsd" | os = "macos")}
-    "CC=musl-gcc" {ocaml-option-musl:installed & os-distribution != "alpine"}
-    "CFLAGS=-Os" {ocaml-option-musl:installed}
-    "LDFLAGS=-Wl,--no-as-needed,-ldl"
-      {ocaml-option-leak-sanitizer:installed |
-       ocaml-option-address-sanitizer:installed & os != "macos"}
-    "CC=gcc -ldl -fsanitize=leak -fno-omit-frame-pointer -O1 -g"
-      {ocaml-option-leak-sanitizer:installed}
-    "CC=gcc -ldl -fsanitize=address -fno-omit-frame-pointer -O1 -g"
-      {ocaml-option-address-sanitizer:installed & os != "macos"}
-    "CC=clang -fsanitize=address -fno-omit-frame-pointer -O1 -g"
-      {ocaml-option-address-sanitizer:installed & os = "macos"}
-    "CC=gcc -m32" {ocaml-option-32bit:installed & os = "linux"}
-    "CC=gcc -Wl,-read_only_relocs,suppress -arch i386 -m32"
-      {ocaml-option-32bit:installed & os = "macos"}
-    "ASPP=cc -c"
-      {!ocaml-option-32bit:installed & !ocaml-option-musl:installed &
-       (os = "openbsd" | os = "macos")}
-    "ASPP=musl-gcc -c"
-      {ocaml-option-musl:installed & os-distribution != "alpine"}
-    "ASPP=gcc -m32 -c" {ocaml-option-32bit:installed & os = "linux"}
-    "ASPP=gcc -arch i386 -m32 -c"
-      {ocaml-option-32bit:installed & os = "macos"}
-    "AS=as --32" {ocaml-option-32bit:installed & os = "linux"}
-    "AS=as -arch i386" {ocaml-option-32bit:installed & os = "macos"}
-    "--host=i386-linux" {ocaml-option-32bit:installed & os = "linux"}
-    "--host=i386-apple-darwin13.2.0"
-      {ocaml-option-32bit:installed & os = "macos"}
-    "PARTIALLD=ld -r -melf_i386"
-      {ocaml-option-32bit:installed & os = "linux"}
-    "LIBS=-static" {ocaml-option-static:installed}
-    "--disable-warn-error"
-  ]
-  [make "-j%{jobs}%"]
-]
-install: [make "install"]
-build-env: [
-  [LSAN_OPTIONS = "detect_leaks=0,exitcode=0"]
-  [ASAN_OPTIONS = "detect_leaks=0,exitcode=0"]
-]
-post-messages: [
-  """\
-A failure in the middle of the build may be caused by build parallelism
-   (enabled by default).
-   See https://github.com/ocaml/opam-repository/pull/14257 for more info."""
-    {failure & jobs > "1" & os != "cygwin"}
-  """\
-You can try installing again including --jobs=1
-   to force a sequential build instead."""
-    {failure & jobs > "1" & os != "cygwin" & opam-version >= "2.0.5"}
-]
-dev-repo: "git+https://github.com/ocaml/ocaml.git"
-url {
-  src: "__OCAML_COMPILER_SRC__"
-}
diff --git a/.github/opam/ocaml-variants.opam.windows b/.github/opam/ocaml-variants.opam.windows
deleted file mode 100644
index 0dbe3bd70..000000000
--- a/.github/opam/ocaml-variants.opam.windows
+++ /dev/null
@@ -1,121 +0,0 @@
-opam-version: "2.0"
-synopsis: "Custom compiler __OCAML_COMPILER_FULL_VERSION__"
-license: "LGPL-2.1-or-later WITH OCaml-LGPL-linking-exception"
-maintainer: "platform@lists.ocaml.org"
-authors: ["Xavier Leroy" "Damien Doligez" "Alain Frisch" "Jacques Garrigue" "Didier Rémy" "Jérôme Vouillon"]
-homepage: "https://ocaml.org"
-bug-reports: "https://github.com/ocaml-multicore/multicoretests/issues"
-dev-repo: "git+https://github.com/ocaml/ocaml.git"
-depends: [
-  "ocaml" {= "__OCAML_OPAM_PACKAGE_VERSION__" & post}
-  "base-unix" {post}
-  "base-bigarray" {post}
-  "base-threads" {post}
-  "base-domains" {post}
-  "base-nnp" {post}
-  "ocaml-option-bytecode-only" {arch != "arm64" & arch != "x86_64"}
-  "conf-flexdll" {os = "cygwin"}
-  ("flexdll" {os = "win32"} | "flexdll-bin" {os = "win32"} & "flexlink" {os = "win32" & post})
-]
-conflict-class: "ocaml-core-compiler"
-flags: compiler
-setenv: CAML_LD_LIBRARY_PATH = "%{lib}%/stublibs"
-build-env: [
-  [PATH += "%{lib}%/%{flexdll-bin:installed?flexdll-bin:ocaml}%"]
-  [LSAN_OPTIONS = "detect_leaks=0,exitcode=0"]
-  [ASAN_OPTIONS = "detect_leaks=0,exitcode=0"]
-]
-build: [
-  [
-    # General configuration
-    "./configure" "-C" "--prefix=%{prefix}%" "--docdir=%{doc}%/ocaml"
-
-    # Windows-specific configuration
-    "--with-flexdll=%{flexdll:share}%" {flexdll:installed}
-
-    # Options
-    "--disable-warn-error"
-
-    "--enable-native-compiler" {!ocaml-option-bytecode-only:installed}
-    "--disable-native-compiler" {ocaml-option-bytecode-only:installed}
-
-    "--with-afl" {ocaml-option-afl:installed}
-    "--disable-flat-float-array" {ocaml-option-no-flat-float-array:installed}
-    "--enable-flambda" {ocaml-option-flambda:installed}
-    "--enable-frame-pointers" {ocaml-option-fp:installed}
-
-    "LIBS=-static" {ocaml-option-static:installed}
-
-    # Force use of cc for macOS and OpenBSD
-    "CC=cc" {!ocaml-option-32bit:installed & !ocaml-option-musl:installed & (os="openbsd"|os="macos")}
-    "ASPP=cc -c" {!ocaml-option-32bit:installed & !ocaml-option-musl:installed & (os="openbsd"|os="macos")}
-
-    # Windows ports
-    "--build=x86_64-pc-cygwin" {os = "win32" & arch = "x86_64"}
-    "--build=i686-pc-cygwin" {os = "win32" & arch = "i686"}
-    # Fix on Cygwin
-    "--enable-imprecise-c99-float-ops" {os = "cygwin"}
-
-    "--host=i686-w64-mingw32" {ocaml-option-mingw:installed & ocaml-option-32bit:installed}
-    "--host=x86_64-w64-mingw32" {ocaml-option-mingw:installed & !ocaml-option-32bit:installed}
-    "--host=i686-pc-windows" {ocaml-option-msvc:installed & ocaml-option-32bit:installed}
-    "--host=x86_64-pc-windows" {ocaml-option-msvc:installed & !ocaml-option-32bit:installed}
-
-    # Compilation with musl
-    "CC=musl-gcc" {ocaml-option-musl:installed & os-distribution!="alpine"}
-    "CFLAGS=-Os" {ocaml-option-musl:installed}
-    "ASPP=musl-gcc -c" {ocaml-option-musl:installed & os-distribution!="alpine"}
-
-    # Compilation with sanitisers
-    "LDFLAGS=-Wl,--no-as-needed,-ldl" {ocaml-option-leak-sanitizer:installed | (ocaml-option-address-sanitizer:installed & os!="macos")}
-    "CC=gcc -ldl -fsanitize=leak -fno-omit-frame-pointer -O1 -g" {ocaml-option-leak-sanitizer:installed}
-    "CC=gcc -ldl -fsanitize=address -fno-omit-frame-pointer -O1 -g" {ocaml-option-address-sanitizer:installed & os!="macos"}
-    "CC=clang -fsanitize=address -fno-omit-frame-pointer -O1 -g" {ocaml-option-address-sanitizer:installed & os="macos"}
-
-    # 32-bit compilation (Linux)
-    "--host=i386-pc-linux-gnu" {ocaml-option-32bit:installed & os="linux"}
-    "CC=gcc -m32" {ocaml-option-32bit:installed & os="linux"}
-    "AS=as --32" {ocaml-option-32bit:installed & os="linux"}
-    "ASPP=gcc -m32 -c" {ocaml-option-32bit:installed & os="linux"}
-    "PARTIALLD=ld -r -melf_i386" {ocaml-option-32bit:installed & os="linux"}
-
-    # 32-bit compilation (macOS)
-    "--host=i386-apple-darwin" {ocaml-option-32bit:installed & os="macos"}
-    "CC=gcc -Wl,-read_only_relocs,suppress -arch i386 -m32" {ocaml-option-32bit:installed & os="macos"}
-    "AS=as -arch i386" {ocaml-option-32bit:installed & os="macos"}
-    "ASPP=gcc -arch i386 -m32 -c" {ocaml-option-32bit:installed & os="macos"}
-  ]
-  [make "-j%{jobs}%"]
-]
-install: [make "install"]
-url {
-  src: "__OCAML_COMPILER_SRC__"
-}
-post-messages: [
-  "A failure in the middle of the build may be caused by build parallelism
-   (enabled by default).
-   Please file a bug report at https://github.com/ocaml/opam-repository/issues"
-  {failure & jobs > 1}
-  "You can try installing again including --jobs=1
-   to force a sequential build instead."
-  {failure & jobs > 1 & opam-version >= "2.0.5"}
-]
-conflicts: [ "ocaml-option-fp" "ocaml-option-msvc" ]
-depopts: [
-  "ocaml-option-32bit"
-  "ocaml-option-afl"
-  "ocaml-option-bytecode-only"
-  "ocaml-option-no-flat-float-array"
-  "ocaml-option-flambda"
-  "ocaml-option-musl"
-  "ocaml-option-leak-sanitizer"
-  "ocaml-option-address-sanitizer"
-  "ocaml-option-static"
-  "ocaml-option-mingw"
-  # TODO: the full behaviour for Cygwin _should_ be that if the Cygwin flexdll is installed and opam's flexdll is not requested,
-  #       then use it; if Cygwin's flexdll is _not_ installed then the opam flexdll package should be pulled in (4.13+) or the
-  #       depext system should cause flexdll to be installed (4.12 and earlier). If opam's flexdll is explicitly requested, then
-  #       OCaml should recompile with it.
-  "flexdll"
-]
-available: os = "win32" | os = "cygwin"
diff --git a/.github/runner.sh b/.github/runner.sh
new file mode 100755
index 000000000..519975e7d
--- /dev/null
+++ b/.github/runner.sh
@@ -0,0 +1,211 @@
+#!/bin/sh
+
+set -e
+
+OCAMLDIR=ocaml
+DUNEDIR=dune
+MULTICORETESTSDIR=multicoretests
+
+fatal() {
+  printf %s "$1"
+  exit 1
+}
+
+compiler_sha() {
+  # Expect $COMPILER_REPO and $COMPILER_REF to be set
+  # Note: only GitHub-hosted compiler forks are supported for now
+  git ls-remote "https://github.com/$COMPILER_REPO.git" "$COMPILER_REF" \
+    | cut -f 1
+}
+
+setup() {
+  if [ -n "$GITHUB_ENV" ] && [ -n "$GITHUB_PATH" ] ; then
+    sha="$(compiler_sha)" || fatal "Cannot find compiler's SHA"
+    arch="$(uname -m)"
+    opts="$(printf %s "$OCAML_OPTIONS" | tr " " -)"
+    opts="${opts:+-}$opts"
+    echo "cache_key=ocaml-$sha-$OCAML_PLATFORM-$arch$opts" >> "$GITHUB_ENV"
+    case "$OCAML_PLATFORM" in
+      mingw|msvc|cygwin)
+        PREFIX='D:\ocaml'
+        bin='D:\ocaml\bin'
+        ;;
+      *)
+        PREFIX="$HOME/local"
+        bin="$HOME/local/bin"
+        ;;
+    esac
+    printf "PREFIX=%s\n" "$PREFIX" >> "$GITHUB_ENV"
+    printf "%s\n" "$bin" >> "$GITHUB_PATH"
+    if [ -z "$JOBS" ] ; then
+      if command -v nproc > /dev/null; then
+        echo "JOBS=$(nproc)" >> "$GITHUB_ENV"
+      elif command -v sysctl > /dev/null; then
+        echo "JOBS=$(sysctl -n hw.ncpu)" >> "$GITHUB_ENV"
+      fi
+    fi
+
+    echo Environment set up:
+    cat "$GITHUB_ENV"
+    echo PATH addition:
+    cat "$GITHUB_PATH"
+  fi
+
+  case "$OCAML_PLATFORM,$OCAML_OPTIONS" in
+    linux,*32bit*)
+      sudo dpkg --add-architecture i386
+      sudo apt-get update
+      sudo apt-get install pkg-config:i386 libzstd1:i386 libzstd-dev:i386 \
+        libgcc-s1:i386 gcc-multilib g++-multilib
+      ;;
+  esac
+}
+
+build_ocaml() {
+  echo "${LOGBEGINGRP}Building OCaml"
+  # We let standard OCaml CI test for warnings
+  opts="--disable-warn-error \
+        --disable-stdlib-manpages \
+        --disable-ocamltest \
+        --disable-ocamldoc"
+  case "$OCAML_OPTIONS" in
+    *fp*)
+      opts="$opts --enable-frame-pointers"
+      ;;
+  esac
+  case "$OCAML_OPTIONS" in
+    *bytecode-only*)
+      opts="$opts --disable-native-compiler"
+      ;;
+  esac
+  case "$OCAML_PLATFORM" in
+    msvc|mingw|cygwin)
+      opts="$opts --prefix=/cygdrive/d/ocaml"
+      ;;
+    *)
+      opts="$opts --prefix=$PREFIX"
+      ;;
+  esac
+
+  cd "$OCAMLDIR"
+  case "$OCAML_PLATFORM,$OCAML_OPTIONS" in
+    msvc,*32bit*)
+      eval $(tools/msvs-promote-path)
+      printf 'Running: %s\n' "./configure --host=i686-pc-windows $opts"
+      if ! ./configure --host=i686-pc-windows $opts ; then
+        cat config.log
+        exit 1
+      fi
+      ;;
+    msvc,*)
+      eval $(tools/msvs-promote-path)
+      printf 'Running: %s\n' "./configure --host=x86_64-pc-windows $opts"
+      if ! ./configure --host=x86_64-pc-windows $opts ; then
+        cat config.log
+        exit 1
+      fi
+      ;;
+    mingw,*)
+      printf 'Running: %s\n' "./configure --host=x86_64-w64-mingw32 $opts"
+      if ! ./configure --host=x86_64-w64-mingw32 $opts ; then
+        cat config.log
+        exit 1
+      fi
+      ;;
+    cygwin,*)
+      case $COMPILER_REF in
+        */5.1*)
+          git -C flexdll fetch origin 0.43
+          git -C flexdll checkout FETCH_HEAD
+          ;;
+      esac
+
+      printf 'Running: %s\n' "./configure $opts"
+      if ! ./configure $opts ; then
+        cat config.log
+        exit 1
+      fi
+      ;;
+    linux,*32bit*)
+      printf 'Running: %s\n' \
+        "./configure --host=i386-linux \"CC=gcc -m32\" $opts"
+      if ! ./configure --host=i386-linux "CC=gcc -m32" $opts ; then
+        cat config.log
+        exit 1
+      fi
+      ;;
+    *) # linux, macos, default options
+      printf 'Running: %s\n' "./configure $opts"
+      if ! ./configure $opts ; then
+        cat config.log
+        exit 1
+      fi
+      ;;
+  esac
+
+  make -j"$JOBS"
+  make install
+
+  echo "$LOGENDGRP"
+}
+
+build_dune() {
+  echo "${LOGBEGINGRP}Building dune"
+  case "$OCAML_PLATFORM" in
+    msvc)
+      eval $("$OCAMLDIR"/tools/msvs-promote-path)
+      ;;
+  esac
+
+  cd "$DUNEDIR"
+  make release
+  make install PREFIX="$PREFIX"
+  echo "$LOGENDGRP"
+}
+
+show_config() {
+  set -x
+  ocamlc -config
+  dune --version
+}
+
+build_testsuite() {
+  case "$OCAML_PLATFORM" in
+    msvc)
+      eval $("$OCAMLDIR"/tools/msvs-promote-path)
+      ;;
+  esac
+
+  cd "$MULTICORETESTSDIR"
+  dune build
+  dune build test/
+}
+
+case "$1" in
+  setup)
+    setup
+    ;;
+  ocaml)
+    build_ocaml
+    ;;
+  dune)
+    build_dune
+    ;;
+  show_config)
+    show_config
+    ;;
+  build)
+    build_testsuite
+    ;;
+  testsuite)
+    cd "$MULTICORETESTSDIR"
+    dune build @ci -j1 --no-buffer --display=quiet --cache=disabled --error-reporting=twice
+    ;;
+  internaltests)
+    cd "$MULTICORETESTSDIR"
+    dune runtest -j1 --no-buffer --display=quiet --cache=disabled --error-reporting=twice test/
+    ;;
+  *)
+    fatal "Unknown command '$1'"
+    ;;
+esac
diff --git a/.github/workflows/common.yml b/.github/workflows/common.yml
index 15157a2f3..939a75e12 100644
--- a/.github/workflows/common.yml
+++ b/.github/workflows/common.yml
@@ -11,11 +11,16 @@ on:
         description: 'Type of machine + OS on which to run the tests'
         type: string
         default: 'ubuntu-latest'
-      cygwin:
-        description: >
-          Whether Cygwin should be used on Windows
-        type: boolean
-        default: false
+      options:
+        description: >-
+          Configuration options for the compiler.
+          Space-separated list of '32bit', 'bytecode-only', 'fp'.
+        type: string
+        default: ''
+      platform:
+        description: 'Platform. One of: linux, macos, msvc, mingw, cygwin.'
+        type: string
+        default: 'linux'
       timeout:
         description: 'Timeout'
         type: number
@@ -32,249 +37,128 @@ on:
         description: 'dune alias that should be built in the main step'
         type: string
         default: 'runtest'
-      compiler:
-        description: 'Compiler to use'
-        type: string
-        default: 'ocaml-base-compiler.5.0.0'
-      compiler_commit:
-        description: 'Version (commit) of the OCaml compiler to use'
-        type: string
-        default: ''
-      compiler_git_ref:
-        description: |
-          Git ref (such as "refs/heads/trunk") of the compiler, to set up caching properly when "compiler" is not a unique identifier
-          This ref will be looked up in the upstream "ocaml/ocaml" github repository
+      compiler_repository:
+        description: 'Repository from which to fetch the compiler'
         type: string
-        default: ''
-      custom_compiler_version:
-        description: |
-          Version number of the custom OCaml compiler to install (eg 5.1.0+gite4954296e68)
-          This version number will be used by setup-ocaml in its cache key so, if it identifies a precise commit, `compiler_git_ref` can be empty
-        type: string
-        default: ''
-      custom_compiler_src:
-        description: |
-          Source (URL) of the custom OCaml compiler to install (eg https://github.com/ocaml/ocaml/archive/e4954296e68.tar.gz)
-          Must be set if custom_compiler_version is
-        type: string
-        default: ''
-      custom_ocaml_package_version:
-        description: |
-          Version number of the OCaml OPAM package to use
-          Defaults to custom_compiler_version chunked at [+~-]
+        default: 'ocaml/ocaml'
+      compiler_ref:
+        description: 'Git reference to use'
         type: string
-        default: ''
+        required: true
+
+permissions: {}
 
 jobs:
   test:
     env:
       QCHECK_MSG_INTERVAL:      '60'
+      OCAML_OPTIONS:            ${{ inputs.options }}
+      OCAML_PLATFORM:           ${{ inputs.platform }}
       DUNE_PROFILE:             ${{ inputs.dune_profile }}
       OCAMLRUNPARAM:            ${{ inputs.runparam }}
       DUNE_CI_ALIAS:            ${{ inputs.dune_alias }}
-      COMPILER:                 ${{ inputs.compiler }}
-      OCAML_COMPILER_GIT_REF:   ${{ inputs.compiler_git_ref }}
-      CUSTOM_COMPILER_VERSION:  ${{ inputs.custom_compiler_version }}
-      CUSTOM_COMPILER_SRC:      ${{ inputs.custom_compiler_src }}
-      CUSTOM_OCAML_PKG_VERSION: ${{ inputs.custom_ocaml_package_version }}
+      COMPILER_REPO:            ${{ inputs.compiler_repository }}
+      COMPILER_REF:             ${{ inputs.compiler_ref }}
+      LOGBEGINGRP:              "::group::"
+      LOGENDGRP:                "::endgroup::"
 
-      # For the record, here is how to set up the environment to test
-      # a PR-version of the compiler
-      # OCAML_COMPILER_GIT_REF:   'refs/pull/12345/head'
-      # CUSTOM_COMPILER_VERSION:  '5.1.0+pr12345'
-      # CUSTOM_COMPILER_SRC:      'https://github.com/ocaml/ocaml/archive/refs/pull/12345/head.tar.gz'
+      # For the record, PR 12345 of the compiler can be tested simply by setting
+      # COMPILER_REF:             'refs/pull/12345/head'
 
     runs-on: ${{ inputs.runs_on }}
 
     timeout-minutes: ${{ inputs.timeout }}
 
     steps:
-      - name: Configure environment (Cygwin)
+      - name: Configure EOLs on Cygwin
         run: |
           # Ensure that .expected files are not modified by check out
           # as, in Cygwin, the .expected should use LF line endings,
           # rather than Windows’ CRLF
           git config --global core.autocrlf input
-
-          # Set up OPAM environment variables for the particular
-          # Cygwin case
-          echo OPAMYES=1 >> $env:GITHUB_ENV
-          echo OPAMROOT=/cygdrive/d/opam >> $env:GITHUB_ENV
-        if: "runner.os == 'Windows' && inputs.cygwin"
+        if: inputs.platform == 'cygwin'
 
       - name: Checkout code
         uses: actions/checkout@v4
-
-      - name: Pre-setup ($PATH, cache prefix, custom OPAM package for the compiler)
-        id: presetup
-        shell: bash
-        run: |
-          if [ "${COMPILER##*32bit}" = "" ]; then
-            sudo dpkg --add-architecture i386
-            sudo apt-get update
-            sudo apt-get install pkg-config:i386 libzstd1:i386 libzstd-dev:i386 libgcc-s1:i386
-          fi
-
-          # Generate an OPAM config for a custom compiler
-          if [ -n "$CUSTOM_COMPILER_VERSION" ]; then
-            if [ -z "$CUSTOM_COMPILER_SRC" ]; then
-              echo '::error title=$CUSTOM_COMPILER_SRC not set::$CUSTOM_COMPILER_SRC must be set whenever $CUSTOM_COMPILER_VERSION is'
-              exit 1
-            fi
-            if [ -z "$CUSTOM_OCAML_PKG_VERSION" ]; then
-              CUSTOM_OCAML_PKG_VERSION="${CUSTOM_COMPILER_VERSION%%[~+-]*}"
-            fi
-            if [ "$RUNNER_OS" = "Windows" ]; then
-              OPAMTEMPLATE=.github/opam/ocaml-variants.opam.windows
-            else
-              OPAMTEMPLATE=.github/opam/ocaml-variants.opam.unix
-            fi
-            OPAMDIR=".github/opam/custom/packages/ocaml-variants/ocaml-variants.$CUSTOM_COMPILER_VERSION"
-            mkdir -p "$OPAMDIR"
-            awk -v compiler="$CUSTOM_COMPILER_VERSION"               \
-                -v compilersrc="$CUSTOM_COMPILER_SRC"                \
-                -v ocamlpkg="$CUSTOM_OCAML_PKG_VERSION"              \
-                '{ sub("__OCAML_COMPILER_FULL_VERSION__", compiler); \
-                   sub("__OCAML_COMPILER_SRC__", compilersrc);       \
-                   sub("__OCAML_OPAM_PACKAGE_VERSION__", ocamlpkg);  \
-                   print }' < $OPAMTEMPLATE                          \
-                   > "$OPAMDIR/opam"
-            echo Generated OPAM package configuration:
-            echo ------------------------------------------------
-            cat "$OPAMDIR/opam"
-            echo ------------------------------------------------
-
-            # Reset $COMPILER keeping the options
-            if [ "${COMPILER##*,*}" "=" "$COMPILER" ];
-            then OPTS="";
-            else OPTS=",${COMPILER#*,}";
-            fi
-            echo "COMPILER=ocaml-variants.$CUSTOM_COMPILER_VERSION$OPTS" >> "$GITHUB_ENV"
-            cat "$GITHUB_ENV"
-          fi
-
-          # Pick up a robust cache prefix
-          if [ -n "$OCAML_COMPILER_GIT_REF" ]; then
-            cache_prefix="$(git ls-remote https://github.com/ocaml/ocaml.git "$OCAML_COMPILER_GIT_REF" | cut -f 1 | head -n 1)"
-          else
-            cache_prefix=v1
-          fi
-          echo "cache_prefix=$cache_prefix" >> "$GITHUB_OUTPUT"
-          cat "$GITHUB_OUTPUT"
-
-          # Save pristine PATH for cache action (Cygwin messes it up)
-          echo "cache_path=$PATH" >> "$GITHUB_OUTPUT"
-
-      - name: Install OCaml compiler ${{ env.COMPILER }} (Linux / macOS)
-        uses: ocaml/setup-ocaml@v2
         with:
-          ocaml-compiler: ${{ env.COMPILER }}
-          opam-repositories: |
-            local: file://${{ github.workspace }}/.github/opam/custom
-            default: https://github.com/ocaml/opam-repository.git
-            override: https://github.com/shym/custom-opam-repository.git
-          opam-depext: false
-          dune-cache: true
-          cache-prefix: ${{ steps.presetup.outputs.cache_prefix }}
-        if: runner.os != 'Windows'
+          path: multicoretests
 
-      - name: Install OCaml compiler ${{ env.COMPILER }} (Windows)
-        uses: ocaml/setup-ocaml@v2
+      - name: Fetch QCheck
+        uses: actions/checkout@v4
         with:
-          ocaml-compiler: ${{ env.COMPILER }}
-          opam-repositories: |
-            local: ${{ github.workspace }}\.github\opam\custom
-            dra27: https://github.com/dra27/opam-repository.git#windows-5.0
-            override: https://github.com/shym/custom-opam-repository.git
-            default: https://github.com/ocaml-opam/opam-repository-mingw.git#sunset
-            upstream: https://github.com/ocaml/opam-repository.git
-          opam-depext: false
-          cache-prefix: ${{ steps.presetup.outputs.cache_prefix }}
-        if: "runner.os == 'Windows' && !inputs.cygwin"
+          repository: c-cube/qcheck
+          ref: v0.22
+          path: multicoretests/qcheck
 
-      - name: Restore Cygwin packages (Cygwin)
-        uses: actions/cache/restore@v3
-        id: cache_cygwin
-        env:
-          PATH: ${{ steps.presetup.outputs.cache_path }}
+      - name: Pre-Setup
+        run: |
+          bash multicoretests/.github/runner.sh setup
+
+      - name: Set up MSVC
+        uses: ilammy/msvc-dev-cmd@v1
+        if: inputs.platform == 'msvc'
+
+      - name: Restore cache
+        uses: actions/cache/restore@v4
+        id: cache
         with:
           path: |
+            ${{ env.PREFIX }}
             C:\cygwin-packages
-          key: cygwin-packages-opam-2.0.7-1
-        if: "runner.os == 'Windows' && inputs.cygwin"
+          key: ${{ env.cache_key }}
 
-      - name: Install Cygwin (in particular OPAM) (Cygwin)
+      - name: Install Cygwin (Windows only)
         uses: cygwin/cygwin-install-action@v4
         with:
-          packages: opam
+          packages: make,bash${{ inputs.platform == 'mingw' && ',mingw64-x86_64-gcc-core,mingw64-x86_64-gcc-g++' || '' }}${{ inputs.platform == 'cygwin' && ',gcc-core' }}
           install-dir: 'D:\cygwin'
-        if: "runner.os == 'Windows' && inputs.cygwin"
+        if: runner.os == 'Windows'
 
-      - name: Save Cygwin packages (Cygwin)
-        uses: actions/cache/save@v3
-        env:
-          PATH: ${{ steps.presetup.outputs.cache_path }}
+      - name: Fetch OCaml
+        uses: actions/checkout@v4
         with:
-          path: |
-            C:\cygwin-packages
-          key: cygwin-packages-opam-2.0.7-1
-        if: "runner.os == 'Windows' && inputs.cygwin && steps.cache_cygwin.outputs.cache-hit != 'true'"
-
-      - name: Restore OPAM state (Cygwin)
-        uses: actions/cache/restore@v3
-        id: cache_opam
-        env:
-          PATH: ${{ steps.presetup.outputs.cache_path }}
+          repository: ${{ env.COMPILER_REPO }}
+          ref: ${{ env.COMPILER_REF }}
+          path: ocaml
+          submodules: true
+        if: steps.cache.outputs.cache-hit != 'true' || inputs.platform == 'msvc'
+        # We need to fetch OCaml in all cases for MSVC for msvs-promote-path
+
+      - name: Fetch dune
+        uses: actions/checkout@v4
         with:
-          path: |
-            D:\opam
-          key: ${{ steps.presetup.outputs.cache_prefix }}-cygwin-opam-${{ env.COMPILER }}
-        if: "runner.os == 'Windows' && inputs.cygwin"
-
-      - name: Install OCaml compiler ${{ env.COMPILER }} (Cygwin)
-        run: |
-          opam init --disable-sandboxing --auto-setup --bare
-          opam repository add --all main "https://github.com/ocaml/opam-repository.git"
-          opam repository add --all windows "https://github.com/ocaml-opam/opam-repository-mingw.git#sunset"
-          opam repository add --all override "https://github.com/shym/custom-opam-repository.git"
-          opam repository add --all dra27 "https://github.com/dra27/opam-repository.git#windows-5.0"
-          opam repository add --all local "./.github/opam/custom/"
-          opam switch create default --repositories=dra27,override,windows,main --packages "${env:COMPILER}"
-        if: "runner.os == 'Windows' && inputs.cygwin && steps.cache_opam.outputs.cache-hit != 'true'"
+          repository: ocaml/dune
+          ref: 3.16.0
+          path: dune
+        if: steps.cache.outputs.cache-hit != 'true'
 
-      - name: Set up macOS environment ($OPAMJOBS)
-        if: runner.os == 'macOS'
+      - name: Build and install OCaml and dune
         run: |
-          echo "OPAMJOBS=1" >> $GITHUB_ENV
+          bash multicoretests/.github/runner.sh ocaml
+          bash multicoretests/.github/runner.sh dune
+        if: steps.cache.outputs.cache-hit != 'true'
 
-      - name: Install Multicore Tests dependencies
-        run: |
-          opam install . --deps-only --with-test
-
-      - name: Show configuration and clean up
-        run: |
-          opam exec -- ocamlc -config
-          opam config list
-          opam exec -- dune printenv
-          opam list --columns=name,installed-version,repository,synopsis-or-target
-          opam clean --all-switches --unused-repositories --logs --download-cache --repo-cache
-
-      - name: Save OPAM state (Cygwin)
-        uses: actions/cache/save@v3
-        env:
-          PATH: ${{ steps.presetup.outputs.cache_path }}
+      - name: Save cache
+        uses: actions/cache/save@v4
         with:
           path: |
-            D:\opam
-          key: ${{ steps.presetup.outputs.cache_prefix }}-cygwin-opam-${{ env.COMPILER }}
-        if: "runner.os == 'Windows' && inputs.cygwin"
+            ${{ env.PREFIX }}
+            C:\cygwin-packages
+          key: ${{ env.cache_key }}
+        if: steps.cache.outputs.cache-hit != 'true'
+
+      - name: Show the configuration
+        run: |
+          bash multicoretests/.github/runner.sh show_config
 
       - name: Build the test suite
-        run: opam exec -- dune build
+        run: |
+          bash multicoretests/.github/runner.sh build
 
       - name: Run the internal package tests
-        run: opam exec -- dune runtest -j1 --no-buffer --display=quiet --cache=disabled --error-reporting=twice test/
+        run: |
+          bash multicoretests/.github/runner.sh internaltests
 
       - name: Run the multicore test suite
-        id: mainstep
-        run: opam exec -- dune build "@ci" -j1 --no-buffer --display=quiet --cache=disabled --error-reporting=twice
+        run: |
+          bash multicoretests/.github/runner.sh testsuite
diff --git a/.github/workflows/cygwin-51x.yml b/.github/workflows/cygwin-51x.yml
index df8c6b4c6..596b58a6e 100644
--- a/.github/workflows/cygwin-51x.yml
+++ b/.github/workflows/cygwin-51x.yml
@@ -11,6 +11,6 @@ jobs:
     uses: ./.github/workflows/common.yml
     with:
       runs_on: windows-latest
-      compiler: ocaml-variants.5.1.1+options+win
-      cygwin: true
+      platform: cygwin
+      compiler_ref: refs/tags/5.1.1
       timeout: 240
diff --git a/.github/workflows/cygwin-520.yml b/.github/workflows/cygwin-520.yml
index 90cafc597..76d3fa87c 100644
--- a/.github/workflows/cygwin-520.yml
+++ b/.github/workflows/cygwin-520.yml
@@ -15,6 +15,6 @@ jobs:
     uses: ./.github/workflows/common.yml
     with:
       runs_on: windows-latest
-      compiler: ocaml-variants.5.2.0+options+win
-      cygwin: true
+      platform: cygwin
+      compiler_ref: refs/tags/5.2.0
       timeout: 240
diff --git a/.github/workflows/cygwin-530-trunk.yml b/.github/workflows/cygwin-530-trunk.yml
index b1b7afd82..9d39a3ba0 100644
--- a/.github/workflows/cygwin-530-trunk.yml
+++ b/.github/workflows/cygwin-530-trunk.yml
@@ -15,7 +15,6 @@ jobs:
     uses: ./.github/workflows/common.yml
     with:
       runs_on: windows-latest
-      compiler: ocaml.5.3.0
-      cygwin: true
-      compiler_git_ref: refs/heads/5.3
+      platform: cygwin
+      compiler_ref: refs/heads/5.3
       timeout: 240
diff --git a/.github/workflows/cygwin-540-trunk.yml b/.github/workflows/cygwin-540-trunk.yml
index b7dd62c01..5de27f4d2 100644
--- a/.github/workflows/cygwin-540-trunk.yml
+++ b/.github/workflows/cygwin-540-trunk.yml
@@ -15,7 +15,6 @@ jobs:
     uses: ./.github/workflows/common.yml
     with:
       runs_on: windows-latest
-      compiler: ocaml.5.4.0
-      cygwin: true
-      compiler_git_ref: refs/heads/trunk
+      platform: cygwin
+      compiler_ref: refs/heads/trunk
       timeout: 240
diff --git a/.github/workflows/linux-500-32bit.yml b/.github/workflows/linux-500-32bit.yml
index 86587a258..2d2069e84 100644
--- a/.github/workflows/linux-500-32bit.yml
+++ b/.github/workflows/linux-500-32bit.yml
@@ -10,5 +10,6 @@ jobs:
   build:
     uses: ./.github/workflows/common.yml
     with:
-      compiler: 'ocaml-variants.5.0.0+options,ocaml-option-32bit'
+      compiler_ref: refs/tags/5.0.0
+      options: 32bit
       timeout: 240
diff --git a/.github/workflows/linux-500-bytecode.yml b/.github/workflows/linux-500-bytecode.yml
index 1014e55d2..ff822129b 100644
--- a/.github/workflows/linux-500-bytecode.yml
+++ b/.github/workflows/linux-500-bytecode.yml
@@ -10,5 +10,6 @@ jobs:
   build:
     uses: ./.github/workflows/common.yml
     with:
-      compiler: 'ocaml-variants.5.0.0+options,ocaml-option-bytecode-only'
+      compiler_ref: refs/tags/5.0.0
+      options: bytecode-only
       timeout: 240
diff --git a/.github/workflows/linux-500-debug.yml b/.github/workflows/linux-500-debug.yml
index 7d1306088..4671b67a1 100644
--- a/.github/workflows/linux-500-debug.yml
+++ b/.github/workflows/linux-500-debug.yml
@@ -10,6 +10,7 @@ jobs:
   build:
     uses: ./.github/workflows/common.yml
     with:
+      compiler_ref: refs/tags/5.0.0
       dune_profile: 'debug-runtime'
       runparam: 's=4096,v=0,V=1'
       timeout: 240
diff --git a/.github/workflows/linux-500.yml b/.github/workflows/linux-500.yml
index d490668b3..8049e76bb 100644
--- a/.github/workflows/linux-500.yml
+++ b/.github/workflows/linux-500.yml
@@ -9,4 +9,5 @@ on:
 jobs:
   build:
     uses: ./.github/workflows/common.yml
-    # default
+    with:
+      compiler_ref: refs/tags/5.0.0
diff --git a/.github/workflows/linux-51x-32bit.yml b/.github/workflows/linux-51x-32bit.yml
index 160f441c9..576125172 100644
--- a/.github/workflows/linux-51x-32bit.yml
+++ b/.github/workflows/linux-51x-32bit.yml
@@ -10,5 +10,6 @@ jobs:
   build:
     uses: ./.github/workflows/common.yml
     with:
-      compiler: 'ocaml-variants.5.1.1+options,ocaml-option-32bit'
+      compiler_ref: refs/tags/5.1.1
+      options: 32bit
       timeout: 240
diff --git a/.github/workflows/linux-51x-bytecode.yml b/.github/workflows/linux-51x-bytecode.yml
index 83532df3c..fd77fa382 100644
--- a/.github/workflows/linux-51x-bytecode.yml
+++ b/.github/workflows/linux-51x-bytecode.yml
@@ -10,5 +10,6 @@ jobs:
   build:
     uses: ./.github/workflows/common.yml
     with:
-      compiler: 'ocaml-variants.5.1.1+options,ocaml-option-bytecode-only'
+      compiler_ref: refs/tags/5.1.1
+      options: bytecode-only
       timeout: 240
diff --git a/.github/workflows/linux-51x-debug.yml b/.github/workflows/linux-51x-debug.yml
index 5a0ae1591..ab29d0b8f 100644
--- a/.github/workflows/linux-51x-debug.yml
+++ b/.github/workflows/linux-51x-debug.yml
@@ -10,7 +10,7 @@ jobs:
   build:
     uses: ./.github/workflows/common.yml
     with:
-      compiler: 'ocaml-base-compiler.5.1.1'
+      compiler_ref: refs/tags/5.1.1
       dune_profile: 'debug-runtime'
       runparam: 's=4096,v=0,V=1'
       timeout: 240
diff --git a/.github/workflows/linux-51x-fp.yml b/.github/workflows/linux-51x-fp.yml
index c98fc25eb..2cf1460a6 100644
--- a/.github/workflows/linux-51x-fp.yml
+++ b/.github/workflows/linux-51x-fp.yml
@@ -10,5 +10,6 @@ jobs:
   build:
     uses: ./.github/workflows/common.yml
     with:
-      compiler: 'ocaml-variants.5.1.1+options,ocaml-option-fp'
+      compiler_ref: refs/tags/5.1.1
+      options: fp
       timeout: 240
diff --git a/.github/workflows/linux-51x.yml b/.github/workflows/linux-51x.yml
index bcc5624f6..81b9191b8 100644
--- a/.github/workflows/linux-51x.yml
+++ b/.github/workflows/linux-51x.yml
@@ -10,4 +10,4 @@ jobs:
   build:
     uses: ./.github/workflows/common.yml
     with:
-      compiler: 'ocaml-base-compiler.5.1.1'
+      compiler_ref: refs/tags/5.1.1
diff --git a/.github/workflows/linux-520-32bit.yml b/.github/workflows/linux-520-32bit.yml
index 76bf62b1f..0d5de1c81 100644
--- a/.github/workflows/linux-520-32bit.yml
+++ b/.github/workflows/linux-520-32bit.yml
@@ -14,5 +14,6 @@ jobs:
   build:
     uses: ./.github/workflows/common.yml
     with:
-      compiler: 'ocaml-variants.5.2.0+options,ocaml-option-32bit'
+      compiler_ref: refs/tags/5.2.0
+      options: 32bit
       timeout: 240
diff --git a/.github/workflows/linux-520-bytecode.yml b/.github/workflows/linux-520-bytecode.yml
index 564b1592a..91d43fcdd 100644
--- a/.github/workflows/linux-520-bytecode.yml
+++ b/.github/workflows/linux-520-bytecode.yml
@@ -14,5 +14,6 @@ jobs:
   build:
     uses: ./.github/workflows/common.yml
     with:
-      compiler: 'ocaml-variants.5.2.0+options,ocaml-option-bytecode-only'
+      compiler_ref: refs/tags/5.2.0
+      options: bytecode-only
       timeout: 240
diff --git a/.github/workflows/linux-520-debug.yml b/.github/workflows/linux-520-debug.yml
index feb3da1df..757b3fedd 100644
--- a/.github/workflows/linux-520-debug.yml
+++ b/.github/workflows/linux-520-debug.yml
@@ -14,7 +14,7 @@ jobs:
   build:
     uses: ./.github/workflows/common.yml
     with:
-      compiler: 'ocaml-base-compiler.5.2.0'
+      compiler_ref: refs/tags/5.2.0
       dune_profile: 'debug-runtime'
       runparam: 's=4096,v=0,V=1'
       timeout: 240
diff --git a/.github/workflows/linux-520-fp.yml b/.github/workflows/linux-520-fp.yml
index 78e7b1608..81762da6a 100644
--- a/.github/workflows/linux-520-fp.yml
+++ b/.github/workflows/linux-520-fp.yml
@@ -14,5 +14,6 @@ jobs:
   build:
     uses: ./.github/workflows/common.yml
     with:
-      compiler: 'ocaml-variants.5.2.0+options,ocaml-option-fp'
+      compiler_ref: refs/tags/5.2.0
+      options: fp
       timeout: 240
diff --git a/.github/workflows/linux-520.yml b/.github/workflows/linux-520.yml
index 026a0d4f6..5209c98b8 100644
--- a/.github/workflows/linux-520.yml
+++ b/.github/workflows/linux-520.yml
@@ -14,4 +14,4 @@ jobs:
   build:
     uses: ./.github/workflows/common.yml
     with:
-      compiler: 'ocaml-base-compiler.5.2.0'
+      compiler_ref: refs/tags/5.2.0
diff --git a/.github/workflows/linux-530-trunk-32bit.yml b/.github/workflows/linux-530-trunk-32bit.yml
index 40923a75e..b5158862c 100644
--- a/.github/workflows/linux-530-trunk-32bit.yml
+++ b/.github/workflows/linux-530-trunk-32bit.yml
@@ -14,6 +14,6 @@ jobs:
   build:
     uses: ./.github/workflows/common.yml
     with:
-      compiler: 'ocaml-variants.5.3.0+trunk,ocaml-option-32bit'
-      compiler_git_ref: refs/heads/5.3
+      compiler_ref: refs/heads/5.3
+      options: 32bit
       timeout: 240
diff --git a/.github/workflows/linux-530-trunk-bytecode.yml b/.github/workflows/linux-530-trunk-bytecode.yml
index 5c696692e..90c056683 100644
--- a/.github/workflows/linux-530-trunk-bytecode.yml
+++ b/.github/workflows/linux-530-trunk-bytecode.yml
@@ -14,6 +14,6 @@ jobs:
   build:
     uses: ./.github/workflows/common.yml
     with:
-      compiler: 'ocaml-variants.5.3.0+trunk,ocaml-option-bytecode-only'
-      compiler_git_ref: refs/heads/5.3
+      compiler_ref: refs/heads/5.3
+      options: bytecode-only
       timeout: 240
diff --git a/.github/workflows/linux-530-trunk-debug.yml b/.github/workflows/linux-530-trunk-debug.yml
index 5c7a2d29e..78c6b32cd 100644
--- a/.github/workflows/linux-530-trunk-debug.yml
+++ b/.github/workflows/linux-530-trunk-debug.yml
@@ -14,8 +14,7 @@ jobs:
   build:
     uses: ./.github/workflows/common.yml
     with:
-      compiler: 'ocaml-variants.5.3.0+trunk'
-      compiler_git_ref: refs/heads/5.3
+      compiler_ref: refs/heads/5.3
       dune_profile: 'debug-runtime'
       runparam: 's=4096,v=0,V=1'
       timeout: 240
diff --git a/.github/workflows/linux-530-trunk-fp.yml b/.github/workflows/linux-530-trunk-fp.yml
index 3c52e7208..3faf669c7 100644
--- a/.github/workflows/linux-530-trunk-fp.yml
+++ b/.github/workflows/linux-530-trunk-fp.yml
@@ -14,6 +14,6 @@ jobs:
   build:
     uses: ./.github/workflows/common.yml
     with:
-      compiler: 'ocaml-variants.5.3.0+trunk,ocaml-option-fp'
-      compiler_git_ref: refs/heads/5.3
+      compiler_ref: refs/heads/5.3
+      options: fp
       timeout: 240
diff --git a/.github/workflows/linux-530-trunk.yml b/.github/workflows/linux-530-trunk.yml
index 01c657076..26f4820ac 100644
--- a/.github/workflows/linux-530-trunk.yml
+++ b/.github/workflows/linux-530-trunk.yml
@@ -14,5 +14,4 @@ jobs:
   build:
     uses: ./.github/workflows/common.yml
     with:
-      compiler: 'ocaml-variants.5.3.0+trunk'
-      compiler_git_ref: refs/heads/5.3
+      compiler_ref: refs/heads/5.3
diff --git a/.github/workflows/linux-540-trunk-32bit.yml b/.github/workflows/linux-540-trunk-32bit.yml
index 455b38e96..d8b367b25 100644
--- a/.github/workflows/linux-540-trunk-32bit.yml
+++ b/.github/workflows/linux-540-trunk-32bit.yml
@@ -14,6 +14,6 @@ jobs:
   build:
     uses: ./.github/workflows/common.yml
     with:
-      compiler: 'ocaml-variants.5.4.0+trunk,ocaml-option-32bit'
-      compiler_git_ref: refs/heads/trunk
+      compiler_ref: refs/heads/trunk
+      options: 32bit
       timeout: 240
diff --git a/.github/workflows/linux-540-trunk-bytecode.yml b/.github/workflows/linux-540-trunk-bytecode.yml
index 216a795b7..76bea3e5b 100644
--- a/.github/workflows/linux-540-trunk-bytecode.yml
+++ b/.github/workflows/linux-540-trunk-bytecode.yml
@@ -14,6 +14,6 @@ jobs:
   build:
     uses: ./.github/workflows/common.yml
     with:
-      compiler: 'ocaml-variants.5.4.0+trunk,ocaml-option-bytecode-only'
-      compiler_git_ref: refs/heads/trunk
+      compiler_ref: refs/heads/trunk
+      options: bytecode-only
       timeout: 240
diff --git a/.github/workflows/linux-540-trunk-debug.yml b/.github/workflows/linux-540-trunk-debug.yml
index 2278edd5e..3f5877301 100644
--- a/.github/workflows/linux-540-trunk-debug.yml
+++ b/.github/workflows/linux-540-trunk-debug.yml
@@ -14,8 +14,7 @@ jobs:
   build:
     uses: ./.github/workflows/common.yml
     with:
-      compiler: 'ocaml-variants.5.4.0+trunk'
-      compiler_git_ref: refs/heads/trunk
+      compiler_ref: refs/heads/trunk
       dune_profile: 'debug-runtime'
       runparam: 's=4096,v=0,V=1'
       timeout: 240
diff --git a/.github/workflows/linux-540-trunk-fp.yml b/.github/workflows/linux-540-trunk-fp.yml
index 1dc5760e0..9f12f9e1a 100644
--- a/.github/workflows/linux-540-trunk-fp.yml
+++ b/.github/workflows/linux-540-trunk-fp.yml
@@ -14,6 +14,6 @@ jobs:
   build:
     uses: ./.github/workflows/common.yml
     with:
-      compiler: 'ocaml-variants.5.4.0+trunk,ocaml-option-fp'
-      compiler_git_ref: refs/heads/trunk
+      compiler_ref: refs/heads/trunk
+      options: fp
       timeout: 240
diff --git a/.github/workflows/linux-540-trunk.yml b/.github/workflows/linux-540-trunk.yml
index 1ddd3319f..5e429f04a 100644
--- a/.github/workflows/linux-540-trunk.yml
+++ b/.github/workflows/linux-540-trunk.yml
@@ -14,5 +14,4 @@ jobs:
   build:
     uses: ./.github/workflows/common.yml
     with:
-      compiler: 'ocaml-variants.5.4.0+trunk'
-      compiler_git_ref: refs/heads/trunk
+      compiler_ref: refs/heads/trunk
diff --git a/.github/workflows/macosx-arm64-500.yml b/.github/workflows/macosx-arm64-500.yml
index 6202766cd..65b33757e 100644
--- a/.github/workflows/macosx-arm64-500.yml
+++ b/.github/workflows/macosx-arm64-500.yml
@@ -11,3 +11,5 @@ jobs:
     uses: ./.github/workflows/common.yml
     with:
       runs_on: 'macos-14'
+      platform: macos
+      compiler_ref: refs/tags/5.0.0
diff --git a/.github/workflows/macosx-arm64-51x.yml b/.github/workflows/macosx-arm64-51x.yml
index bfe137c7d..f5e33a392 100644
--- a/.github/workflows/macosx-arm64-51x.yml
+++ b/.github/workflows/macosx-arm64-51x.yml
@@ -10,5 +10,6 @@ jobs:
   build:
     uses: ./.github/workflows/common.yml
     with:
-      compiler: 'ocaml-base-compiler.5.1.1'
       runs_on: 'macos-14'
+      platform: macos
+      compiler_ref: refs/tags/5.1.1
diff --git a/.github/workflows/macosx-arm64-520.yml b/.github/workflows/macosx-arm64-520.yml
index 040164dd7..a9446ac09 100644
--- a/.github/workflows/macosx-arm64-520.yml
+++ b/.github/workflows/macosx-arm64-520.yml
@@ -14,5 +14,6 @@ jobs:
   build:
     uses: ./.github/workflows/common.yml
     with:
-      compiler: 'ocaml-base-compiler.5.2.0'
       runs_on: 'macos-14'
+      platform: macos
+      compiler_ref: refs/tags/5.2.0
diff --git a/.github/workflows/macosx-arm64-530-trunk.yml b/.github/workflows/macosx-arm64-530-trunk.yml
index c920d871a..86f466f01 100644
--- a/.github/workflows/macosx-arm64-530-trunk.yml
+++ b/.github/workflows/macosx-arm64-530-trunk.yml
@@ -14,6 +14,6 @@ jobs:
   build:
     uses: ./.github/workflows/common.yml
     with:
-      compiler: 'ocaml-variants.5.3.0+trunk'
-      compiler_git_ref: refs/heads/5.3
       runs_on: 'macos-14'
+      platform: macos
+      compiler_ref: refs/heads/5.3
diff --git a/.github/workflows/macosx-arm64-540-trunk.yml b/.github/workflows/macosx-arm64-540-trunk.yml
index dc4780fd5..ce405419e 100644
--- a/.github/workflows/macosx-arm64-540-trunk.yml
+++ b/.github/workflows/macosx-arm64-540-trunk.yml
@@ -14,6 +14,6 @@ jobs:
   build:
     uses: ./.github/workflows/common.yml
     with:
-      compiler: 'ocaml-variants.5.4.0+trunk'
-      compiler_git_ref: refs/heads/trunk
       runs_on: 'macos-14'
+      platform: macos
+      compiler_ref: refs/heads/trunk
diff --git a/.github/workflows/macosx-intel-500.yml b/.github/workflows/macosx-intel-500.yml
index 5adee673e..91ae3bbda 100644
--- a/.github/workflows/macosx-intel-500.yml
+++ b/.github/workflows/macosx-intel-500.yml
@@ -11,3 +11,5 @@ jobs:
     uses: ./.github/workflows/common.yml
     with:
       runs_on: 'macos-13'
+      platform: macos
+      compiler_ref: refs/tags/5.0.0
diff --git a/.github/workflows/macosx-intel-51x.yml b/.github/workflows/macosx-intel-51x.yml
index 286cfea45..c54d72bc3 100644
--- a/.github/workflows/macosx-intel-51x.yml
+++ b/.github/workflows/macosx-intel-51x.yml
@@ -10,5 +10,6 @@ jobs:
   build:
     uses: ./.github/workflows/common.yml
     with:
-      compiler: 'ocaml-base-compiler.5.1.1'
       runs_on: 'macos-13'
+      platform: macos
+      compiler_ref: refs/tags/5.1.1
diff --git a/.github/workflows/macosx-intel-520.yml b/.github/workflows/macosx-intel-520.yml
index 0ecb8c954..c16ef7b50 100644
--- a/.github/workflows/macosx-intel-520.yml
+++ b/.github/workflows/macosx-intel-520.yml
@@ -14,5 +14,6 @@ jobs:
   build:
     uses: ./.github/workflows/common.yml
     with:
-      compiler: 'ocaml-base-compiler.5.2.0'
       runs_on: 'macos-13'
+      platform: macos
+      compiler_ref: refs/tags/5.2.0
diff --git a/.github/workflows/macosx-intel-530-trunk.yml b/.github/workflows/macosx-intel-530-trunk.yml
index 4a4117be2..8ae97bb56 100644
--- a/.github/workflows/macosx-intel-530-trunk.yml
+++ b/.github/workflows/macosx-intel-530-trunk.yml
@@ -14,6 +14,6 @@ jobs:
   build:
     uses: ./.github/workflows/common.yml
     with:
-      compiler: 'ocaml-variants.5.3.0+trunk'
-      compiler_git_ref: refs/heads/5.3
       runs_on: 'macos-13'
+      platform: macos
+      compiler_ref: refs/heads/5.3
diff --git a/.github/workflows/macosx-intel-540-trunk.yml b/.github/workflows/macosx-intel-540-trunk.yml
index 19207ce21..bbe4f3738 100644
--- a/.github/workflows/macosx-intel-540-trunk.yml
+++ b/.github/workflows/macosx-intel-540-trunk.yml
@@ -14,6 +14,6 @@ jobs:
   build:
     uses: ./.github/workflows/common.yml
     with:
-      compiler: 'ocaml-variants.5.4.0+trunk'
-      compiler_git_ref: refs/heads/trunk
       runs_on: 'macos-13'
+      platform: macos
+      compiler_ref: refs/heads/trunk
diff --git a/.github/workflows/mingw-500-bytecode.yml b/.github/workflows/mingw-500-bytecode.yml
index d7c2af561..feb56bfab 100644
--- a/.github/workflows/mingw-500-bytecode.yml
+++ b/.github/workflows/mingw-500-bytecode.yml
@@ -11,5 +11,7 @@ jobs:
     uses: ./.github/workflows/common.yml
     with:
       runs_on: windows-latest
-      compiler: ocaml.5.0.0,ocaml-option-mingw,ocaml-option-bytecode-only
+      platform: mingw
+      compiler_ref: refs/tags/5.0.0
+      options: bytecode-only
       timeout: 240
diff --git a/.github/workflows/mingw-500.yml b/.github/workflows/mingw-500.yml
index fa4280550..6a2846714 100644
--- a/.github/workflows/mingw-500.yml
+++ b/.github/workflows/mingw-500.yml
@@ -11,5 +11,6 @@ jobs:
     uses: ./.github/workflows/common.yml
     with:
       runs_on: windows-latest
-      compiler: ocaml.5.0.0,ocaml-option-mingw
+      platform: mingw
+      compiler_ref: refs/tags/5.0.0
       timeout: 240
diff --git a/.github/workflows/mingw-51x-bytecode.yml b/.github/workflows/mingw-51x-bytecode.yml
index bee386453..fc7601896 100644
--- a/.github/workflows/mingw-51x-bytecode.yml
+++ b/.github/workflows/mingw-51x-bytecode.yml
@@ -11,5 +11,7 @@ jobs:
     uses: ./.github/workflows/common.yml
     with:
       runs_on: windows-latest
-      compiler: ocaml-variants.5.1.1+options+win,ocaml-option-mingw,ocaml-option-bytecode-only
+      platform: mingw
+      compiler_ref: refs/tags/5.1.1
+      options: bytecode-only
       timeout: 240
diff --git a/.github/workflows/mingw-51x.yml b/.github/workflows/mingw-51x.yml
index ba83c6cb8..78bdc632c 100644
--- a/.github/workflows/mingw-51x.yml
+++ b/.github/workflows/mingw-51x.yml
@@ -11,5 +11,6 @@ jobs:
     uses: ./.github/workflows/common.yml
     with:
       runs_on: windows-latest
-      compiler: ocaml-variants.5.1.1+options+win,ocaml-option-mingw
+      platform: mingw
+      compiler_ref: refs/tags/5.1.1
       timeout: 240
diff --git a/.github/workflows/mingw-520-bytecode.yml b/.github/workflows/mingw-520-bytecode.yml
index 7afd758bf..07784d974 100644
--- a/.github/workflows/mingw-520-bytecode.yml
+++ b/.github/workflows/mingw-520-bytecode.yml
@@ -15,5 +15,7 @@ jobs:
     uses: ./.github/workflows/common.yml
     with:
       runs_on: windows-latest
-      compiler: ocaml-variants.5.2.0+options+win,ocaml-option-mingw,ocaml-option-bytecode-only
+      platform: mingw
+      compiler_ref: refs/tags/5.2.0
+      options: bytecode-only
       timeout: 240
diff --git a/.github/workflows/mingw-520.yml b/.github/workflows/mingw-520.yml
index 0ad27d86f..2f803c483 100644
--- a/.github/workflows/mingw-520.yml
+++ b/.github/workflows/mingw-520.yml
@@ -15,5 +15,6 @@ jobs:
     uses: ./.github/workflows/common.yml
     with:
       runs_on: windows-latest
-      compiler: ocaml-variants.5.2.0+options+win,ocaml-option-mingw
+      platform: mingw
+      compiler_ref: refs/tags/5.2.0
       timeout: 240
diff --git a/.github/workflows/mingw-530-trunk-bytecode.yml b/.github/workflows/mingw-530-trunk-bytecode.yml
index 8341cc386..753e21ca6 100644
--- a/.github/workflows/mingw-530-trunk-bytecode.yml
+++ b/.github/workflows/mingw-530-trunk-bytecode.yml
@@ -15,6 +15,7 @@ jobs:
     uses: ./.github/workflows/common.yml
     with:
       runs_on: windows-latest
-      compiler: ocaml.5.3.0,ocaml-option-mingw,ocaml-option-bytecode-only
-      compiler_git_ref: refs/heads/5.3
+      platform: mingw
+      compiler_ref: refs/heads/5.3
+      options: bytecode-only
       timeout: 240
diff --git a/.github/workflows/mingw-530-trunk.yml b/.github/workflows/mingw-530-trunk.yml
index 22d580c79..bc3e675ff 100644
--- a/.github/workflows/mingw-530-trunk.yml
+++ b/.github/workflows/mingw-530-trunk.yml
@@ -15,6 +15,6 @@ jobs:
     uses: ./.github/workflows/common.yml
     with:
       runs_on: windows-latest
-      compiler: ocaml.5.3.0,ocaml-option-mingw
-      compiler_git_ref: refs/heads/5.3
+      platform: mingw
+      compiler_ref: refs/heads/5.3
       timeout: 240
diff --git a/.github/workflows/mingw-540-trunk-bytecode.yml b/.github/workflows/mingw-540-trunk-bytecode.yml
index 6e95b96bf..fdb811dae 100644
--- a/.github/workflows/mingw-540-trunk-bytecode.yml
+++ b/.github/workflows/mingw-540-trunk-bytecode.yml
@@ -15,6 +15,7 @@ jobs:
     uses: ./.github/workflows/common.yml
     with:
       runs_on: windows-latest
-      compiler: ocaml.5.4.0,ocaml-option-mingw,ocaml-option-bytecode-only
-      compiler_git_ref: refs/heads/trunk
+      platform: mingw
+      compiler_ref: refs/heads/trunk
+      options: bytecode-only
       timeout: 240
diff --git a/.github/workflows/mingw-540-trunk.yml b/.github/workflows/mingw-540-trunk.yml
index 82691698a..af3abfc6b 100644
--- a/.github/workflows/mingw-540-trunk.yml
+++ b/.github/workflows/mingw-540-trunk.yml
@@ -15,6 +15,6 @@ jobs:
     uses: ./.github/workflows/common.yml
     with:
       runs_on: windows-latest
-      compiler: ocaml.5.4.0,ocaml-option-mingw
-      compiler_git_ref: refs/heads/trunk
+      platform: mingw
+      compiler_ref: refs/heads/trunk
       timeout: 240
diff --git a/.github/workflows/msvc-530-trunk-bytecode.yml b/.github/workflows/msvc-530-trunk-bytecode.yml
index 251738ed6..04916c726 100644
--- a/.github/workflows/msvc-530-trunk-bytecode.yml
+++ b/.github/workflows/msvc-530-trunk-bytecode.yml
@@ -12,7 +12,9 @@ on:
 
 jobs:
   build:
-    uses: ./.github/workflows/msvc-common.yml
+    uses: ./.github/workflows/common.yml
     with:
-      bytecodeonly: true
-      compiler_ref: '5.3'
+      runs_on: windows-latest
+      platform: msvc
+      compiler_ref: refs/heads/5.3
+      options: bytecode-only
diff --git a/.github/workflows/msvc-530-trunk.yml b/.github/workflows/msvc-530-trunk.yml
index 24dda9ddd..c599ee866 100644
--- a/.github/workflows/msvc-530-trunk.yml
+++ b/.github/workflows/msvc-530-trunk.yml
@@ -12,6 +12,8 @@ on:
 
 jobs:
   build:
-    uses: ./.github/workflows/msvc-common.yml
+    uses: ./.github/workflows/common.yml
     with:
-      compiler_ref: '5.3'
+      runs_on: windows-latest
+      platform: msvc
+      compiler_ref: refs/heads/5.3
diff --git a/.github/workflows/msvc-540-trunk-bytecode.yml b/.github/workflows/msvc-540-trunk-bytecode.yml
index 72be4d269..b32e1270d 100644
--- a/.github/workflows/msvc-540-trunk-bytecode.yml
+++ b/.github/workflows/msvc-540-trunk-bytecode.yml
@@ -12,7 +12,9 @@ on:
 
 jobs:
   build:
-    uses: ./.github/workflows/msvc-common.yml
+    uses: ./.github/workflows/common.yml
     with:
-      bytecodeonly: true
-      compiler_ref: 'trunk'
+      runs_on: windows-latest
+      platform: msvc
+      compiler_ref: refs/heads/trunk
+      options: bytecode-only
diff --git a/.github/workflows/msvc-540-trunk.yml b/.github/workflows/msvc-540-trunk.yml
index 018751b58..1d6ee614f 100644
--- a/.github/workflows/msvc-540-trunk.yml
+++ b/.github/workflows/msvc-540-trunk.yml
@@ -12,6 +12,8 @@ on:
 
 jobs:
   build:
-    uses: ./.github/workflows/msvc-common.yml
+    uses: ./.github/workflows/common.yml
     with:
-      compiler_ref: 'trunk'
+      runs_on: windows-latest
+      platform: msvc
+      compiler_ref: refs/heads/trunk
diff --git a/.github/workflows/msvc-common.yml b/.github/workflows/msvc-common.yml
deleted file mode 100644
index afc45fd57..000000000
--- a/.github/workflows/msvc-common.yml
+++ /dev/null
@@ -1,151 +0,0 @@
-name: Common MSVC CI workflow
-
-concurrency:
-  group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
-  cancel-in-progress: true
-
-on:
-  workflow_call:
-    inputs:
-      bytecodeonly:
-        type: boolean
-        default: false
-      dune_alias:
-        description: 'dune alias that should be built in the main step'
-        type: string
-        default: 'runtest'
-      compiler_ref:
-        description: |
-          Git ref (such as "trunk") of the compiler.
-          This ref will be used to checkout the relevant "ocaml/ocaml" github branch.
-        type: string
-        default: ''
-
-
-jobs:
-  build:
-    permissions: {}
-
-    runs-on: windows-latest
-
-    steps:
-      - name: Save pristine PATH
-        id: pristine
-        run: |
-          echo "pristine_path=${env:Path}" >> "${env:GITHUB_OUTPUT}"
-
-      - name: Set up MSVC
-        uses: ilammy/msvc-dev-cmd@v1
-
-      - name: Fetch OCaml
-        uses: actions/checkout@v4
-        with:
-          repository: ocaml/ocaml
-          ref: ${{ inputs.compiler_ref }}
-          path: ocaml
-          submodules: true
-
-      - name: Choose a cache key
-        id: key
-        env:
-          BC_KEY_PART: ${{ inputs.bytecodeonly && '-bytecode' || '' }}
-        run: |
-          git -C ocaml rev-parse HEAD | Tee-Object -Variable sha
-          echo "cache_key=ocaml-msvc${env:BC_KEY_PART}-${sha}" | Tee-Object -FilePath "${env:GITHUB_OUTPUT}"
-
-      - name: Restore cache
-        uses: actions/cache/restore@v3
-        id: cache
-        env:
-          PATH: ${{ steps.pristine.outputs.pristine_path }}
-        with:
-          path: |
-            C:\cygwin-packages
-            D:\ocaml
-          key: ${{ steps.key.outputs.cache_key }}
-
-      - name: Install Cygwin (Cygwin)
-        uses: cygwin/cygwin-install-action@v3
-        with:
-          packages: make,bash
-          install-dir: 'D:\cygwin'
-
-      - name: Build OCaml
-        shell: bash -e {0}
-        env:
-          NATIVE: ${{ inputs.bytecodeonly && '--disable-native-compiler' || '' }}
-        run: |
-          cd ocaml                                                                               #
-          mkdir /cygdrive/d/ocaml                                                                #
-          eval $(tools/msvs-promote-path)                                                        #
-          ./configure --host=x86_64-pc-windows --with-flexdll --prefix=/cygdrive/d/ocaml $NATIVE #
-          make                                                                                   #
-          make install                                                                           #
-        if: "steps.cache.outputs.cache-hit != 'true'"
-
-      - name: Fetch dune
-        uses: actions/checkout@v4
-        with:
-          repository: ocaml/dune
-          path: dune
-        if: "steps.cache.outputs.cache-hit != 'true'"
-
-      - name: Compile dune
-        shell: bash -e {0}
-        run: |
-          export PATH="/cygdrive/d/ocaml/bin:$PATH"                                        #
-          eval $(ocaml/tools/msvs-promote-path)                                            #
-          export INCLUDE="$INCLUDE;$(cygpath -w "$PWD/ocaml/runtime/winpthreads/include")" #
-          cd dune                                                                          #
-          make release                                                                     #
-          make install PREFIX='D:\ocaml'                                                   #
-        if: "steps.cache.outputs.cache-hit != 'true'"
-
-      - name: Display configuration and set up PATH
-        run: |
-          D:\ocaml\bin\ocamlc -config
-          D:\ocaml\bin\dune --version
-          echo "D:\ocaml\bin" >> ${env:GITHUB_PATH}
-
-      - name: Save cache
-        uses: actions/cache/save@v3
-        env:
-          PATH: ${{ steps.pristine.outputs.pristine_path }}
-        with:
-          path: |
-            C:\cygwin-packages
-            D:\ocaml
-          key: ${{ steps.key.outputs.cache_key }}
-        if: "steps.cache.outputs.cache-hit != 'true'"
-
-      - name: Fetch multicoretests
-        uses: actions/checkout@v4
-        with:
-          path: mct
-
-      - name: Fetch QCheck
-        uses: actions/checkout@v4
-        with:
-          repository: c-cube/qcheck
-          path: mct/qcheck
-
-      - name: Build the test suite
-        shell: bash -e {0}
-        run: |
-          eval $(ocaml/tools/msvs-promote-path)     #
-          cd mct                                    #
-          dune build                                #
-          dune build test/                          #
-
-      - name: Run the internal package tests
-        run: |
-          cd mct
-          dune runtest -j1 --no-buffer --display=quiet --cache=disabled --error-reporting=twice test/
-
-      - name: Run the multicore test suite
-        env:
-          QCHECK_MSG_INTERVAL: 60
-          DUNE_CI_ALIAS:       ${{ inputs.dune_alias }}
-        run: |
-          cd mct
-          dune build "@ci" -j1 --no-buffer --display=quiet --cache=disabled --error-reporting=twice
diff --git a/README.md b/README.md
index 5f641c20e..c036ae3aa 100644
--- a/README.md
+++ b/README.md
@@ -142,15 +142,13 @@ It is also possible to run the test suite in the CI, by altering
 [.github/workflows/common.yml](.github/workflows/common.yml) to target
 a particular compiler PR:
 ```
-      OCAML_COMPILER_GIT_REF:   'refs/pull/12345/head'
-      CUSTOM_COMPILER_VERSION:  '5.1.0+pr12345'
-      CUSTOM_COMPILER_SRC:      'https://github.com/ocaml/ocaml/archive/refs/pull/12345/head.tar.gz'
+      COMPILER_REF:             'refs/pull/12345/head'
 ```
 
-or a particular branch:
+or a particular branch of a particular fork:
 ```
-      CUSTOM_COMPILER_VERSION:  '5.1.0+myexperiment'
-      CUSTOM_COMPILER_SRC:      'https://github.com/my_github_id/ocaml/archive/myexperiment-branch.tar.gz'
+      COMPILER_REPO:            'login/ocaml'
+      COMPILER_REF:             'refs/heads/test-me'
 ```