Show panic! messages via debugPrintf, even including some runtime…

… arguments (`{u,i,f}32` as `{}` or `{:?}`).

CHANGELOG.md

@@ -30,6 +30,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## [Unreleased]
 
 ### Added ⭐
+- [PR#1082](https://github.com/EmbarkStudios/rust-gpu/pull/1082) added partial
+  support for extracting `format_args!` from `panic!`s, and converting them to
+  `debugPrintf` calls (if enabled via `ShaderPanicStrategy`), including runtime
+  arguments (`u32`/`i32`/`f32` with `Display`/`Debug` formatting, for now)
 - [PR#1081](https://github.com/EmbarkStudios/rust-gpu/pull/1081) added the ability
   to access SPIR-V specialization constants (`OpSpecConstant`) via entry-point
   inputs declared as `#[spirv(spec_constant(id = ..., default = ...))] x: u32`  

crates/rustc_codegen_spirv/src/builder/builder_methods.rs

@@ -20,11 +20,13 @@ use rustc_codegen_ssa::MemFlags;
 use rustc_data_structures::fx::FxHashSet;
 use rustc_middle::bug;
 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrs;
+use rustc_middle::ty::layout::LayoutOf;
 use rustc_middle::ty::Ty;
 use rustc_span::Span;
 use rustc_target::abi::call::FnAbi;
 use rustc_target::abi::{Abi, Align, Scalar, Size, WrappingRange};
 use smallvec::SmallVec;
+use std::borrow::Cow;
 use std::cell::Cell;
 use std::convert::TryInto;
 use std::iter::{self, empty};
@@ -2414,12 +2416,25 @@ impl<'a, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'tcx> {
             // nor simplified in MIR (e.g. promoted to a constant) in any way,
             // so we have to try and remove the `fmt::Arguments::new` call here.
             #[derive(Default)]
-            struct DecodedFormatArgs {}
+            struct DecodedFormatArgs<'tcx> {
+                /// If fully constant, the `pieces: &'a [&'static str]` input
+                /// of `fmt::Arguments<'a>` (i.e. the strings between args).
+                const_pieces: Option<SmallVec<[String; 2]>>,
+
+                /// Original references for `fmt::Arguments<'a>` dynamic arguments,
+                /// i.e. the `&'a T` passed to `fmt::rt::Argument::<'a>::new_*`,
+                /// tracking the type `T` and `char` formatting specifier.
+                ///
+                /// E.g. for `format_args!("{a} {b:x}")` they'll be:
+                /// * `&a` with `typeof a` and ' ',
+                ///  *`&b` with `typeof b` and 'x'
+                ref_arg_ids_with_ty_and_spec: SmallVec<[(Word, Ty<'tcx>, char); 2]>,
+            }
             struct FormatArgsNotRecognized(String);
 
             // HACK(eddyb) this is basically a `try` block.
             let try_decode_and_remove_format_args = || {
-                let decoded_format_args = DecodedFormatArgs::default();
+                let mut decoded_format_args = DecodedFormatArgs::default();
 
                 let const_u32_as_usize = |ct_id| match self.builder.lookup_const_by_id(ct_id)? {
                     SpirvConst::U32(x) => Some(x as usize),
@@ -2441,6 +2456,32 @@ impl<'a, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'tcx> {
                     }
                     None
                 };
+                let const_str_as_utf8 = |str_ptr_and_len_ids: &[Word]| {
+                    let piece_str_bytes = const_slice_as_elem_ids(str_ptr_and_len_ids)?
+                        .iter()
+                        .map(|&id| u8::try_from(const_u32_as_usize(id)?).ok())
+                        .collect::<Option<Vec<u8>>>()?;
+                    String::from_utf8(piece_str_bytes).ok()
+                };
+
+                // HACK(eddyb) some entry-points only take a `&str`, not `fmt::Arguments`.
+                if let [
+                    SpirvValue {
+                        kind: SpirvValueKind::Def(a_id),
+                        ..
+                    },
+                    SpirvValue {
+                        kind: SpirvValueKind::Def(b_id),
+                        ..
+                    },
+                    _, // `&'static panic::Location<'static>`
+                ] = args[..]
+                {
+                    if let Some(const_msg) = const_str_as_utf8(&[a_id, b_id]) {
+                        decoded_format_args.const_pieces = Some([const_msg].into_iter().collect());
+                        return Ok(decoded_format_args);
+                    }
+                }
 
                 let format_args_id = match args {
                     &[
@@ -2503,6 +2544,7 @@ impl<'a, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'tcx> {
                 #[derive(Debug)]
                 enum Inst<'tcx, ID> {
                     Bitcast(ID, ID),
+                    CompositeExtract(ID, ID, u32),
                     AccessChain(ID, ID, SpirvConst<'tcx>),
                     InBoundsAccessChain(ID, ID, SpirvConst<'tcx>),
                     Store(ID, ID),
@@ -2519,6 +2561,15 @@ impl<'a, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'tcx> {
                         let (i, inst) = non_debug_insts.next_back()?;
                         taken_inst_idx_range.start.set(i);
 
+                        // HACK(eddyb) avoid the logic below that assumes only ID operands
+                        if inst.class.opcode == Op::CompositeExtract {
+                            if let (Some(r), &[Operand::IdRef(x), Operand::LiteralInt32(i)]) =
+                                (inst.result_id, &inst.operands[..])
+                            {
+                                return Some(Inst::CompositeExtract(r, x, i));
+                            }
+                        }
+
                         // HACK(eddyb) all instructions accepted below
                         // are expected to take no more than 4 operands,
                         // and this is easier to use than an iterator.
@@ -2716,6 +2767,26 @@ impl<'a, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'tcx> {
                     }
                 }
 
+                // If the `pieces: &[&str]` slice needs a bitcast, it'll be here.
+                let pieces_slice_ptr_id = match try_rev_take(1).as_deref() {
+                    Some(&[Inst::Bitcast(out_id, in_id)]) if out_id == pieces_slice_ptr_id => in_id,
+                    _ => pieces_slice_ptr_id,
+                };
+                decoded_format_args.const_pieces =
+                    const_slice_as_elem_ids(&[pieces_slice_ptr_id, pieces_len_id]).and_then(
+                        |piece_ids| {
+                            piece_ids
+                                .iter()
+                                .map(|&piece_id| {
+                                    match self.builder.lookup_const_by_id(piece_id)? {
+                                        SpirvConst::Composite(piece) => const_str_as_utf8(piece),
+                                        _ => None,
+                                    }
+                                })
+                                .collect::<Option<_>>()
+                        },
+                    );
+
                 // Keep all instructions up to (but not including) the last one
                 // confirmed above to be the first instruction of `format_args!`.
                 func.blocks[block_idx]
@@ -2725,8 +2796,61 @@ impl<'a, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'tcx> {
                 Ok(decoded_format_args)
             };
 
-            match try_decode_and_remove_format_args() {
-                Ok(DecodedFormatArgs {}) => {}
+            let mut debug_printf_args = SmallVec::<[_; 2]>::new();
+            let message = match try_decode_and_remove_format_args() {
+                Ok(DecodedFormatArgs {
+                    const_pieces,
+                    ref_arg_ids_with_ty_and_spec,
+                }) => {
+                    match const_pieces {
+                        Some(const_pieces) => {
+                            const_pieces
+                                .into_iter()
+                                .map(|s| Cow::Owned(s.replace('%', "%%")))
+                                .interleave(ref_arg_ids_with_ty_and_spec.iter().map(
+                                    |&(ref_id, ty, spec)| {
+                                        use rustc_target::abi::{Integer::*, Primitive::*};
+
+                                        let layout = self.layout_of(ty);
+
+                                        let scalar = match layout.abi {
+                                            Abi::Scalar(scalar) => Some(scalar.primitive()),
+                                            _ => None,
+                                        };
+                                        let debug_printf_fmt = match (spec, scalar) {
+                                            // FIXME(eddyb) support more of these,
+                                            // potentially recursing to print ADTs.
+                                            (' ' | '?', Some(Int(I32, false))) => "%u",
+                                            ('x', Some(Int(I32, false))) => "%x",
+                                            (' ' | '?', Some(Int(I32, true))) => "%i",
+                                            (' ' | '?', Some(F32)) => "%f",
+
+                                            _ => "",
+                                        };
+
+                                        if debug_printf_fmt.is_empty() {
+                                            return Cow::Owned(
+                                                format!("{{/* unprintable {ty} */:{spec}}}")
+                                                    .replace('%', "%%"),
+                                            );
+                                        }
+
+                                        let spirv_type = layout.spirv_type(self.span(), self);
+                                        debug_printf_args.push(
+                                            self.emit()
+                                                .load(spirv_type, None, ref_id, None, [])
+                                                .unwrap()
+                                                .with_type(spirv_type),
+                                        );
+                                        Cow::Borrowed(debug_printf_fmt)
+                                    },
+                                ))
+                                .collect::<String>()
+                        }
+                        None => "<unknown message>".into(),
+                    }
+                }
+
                 Err(FormatArgsNotRecognized(step)) => {
                     if let Some(current_span) = self.current_span {
                         let mut warn = self.tcx.sess.struct_span_warn(
@@ -2738,8 +2862,8 @@ impl<'a, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'tcx> {
                             "compilation may later fail due to leftover `format_args!` internals",
                         );
 
-                        if self.tcx.sess.opts.unstable_opts.inline_mir != Some(true) {
-                            warn.note("missing `-Zinline-mir=on` flag (should've been set by `spirv-builder`)")
+                        if self.tcx.sess.opts.unstable_opts.inline_mir != Some(false) {
+                            warn.note("missing `-Zinline-mir=off` flag (should've been set by `spirv-builder`)")
                                 .help("check `.cargo` and environment variables for potential overrides")
                                 .help("(or, if not using `spirv-builder` at all, add the flag manually)");
                         } else {
@@ -2748,13 +2872,17 @@ impl<'a, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'tcx> {
 
                         warn.emit();
                     }
+                    "<unknown message> (failed to find/decode `format_args!` expansion)".into()
                 }
-            }
+            };
 
             // HACK(eddyb) redirect any possible panic call to an abort, to avoid
             // needing to materialize `&core::panic::Location` or `format_args!`.
-            // FIXME(eddyb) find a way to extract the original message.
-            self.abort_with_message("panicked: <unknown message>".into());
+            self.abort_with_message_and_debug_printf_args(
+                // HACK(eddyb) `|` is an ad-hoc convention of `linker::spirt_passes::controlflow`.
+                format!("panicked|{message}"),
+                debug_printf_args,
+            );
             self.undef(result_type)
         } else if let Some(mode) = buffer_load_intrinsic {
             self.codegen_buffer_load_intrinsic(result_type, args, mode)

crates/rustc_codegen_spirv/src/builder/intrinsics.rs

@@ -339,7 +339,11 @@ impl<'a, 'tcx> IntrinsicCallMethods<'tcx> for Builder<'a, 'tcx> {
     }
 
     fn abort(&mut self) {
-        self.abort_with_message("aborted: intrinsics::abort() called".into());
+        // HACK(eddyb) `|` is an ad-hoc convention of `linker::spirt_passes::controlflow`.
+        self.abort_with_message_and_debug_printf_args(
+            "aborted|intrinsics::abort() called".into(),
+            [],
+        );
     }
 
     fn assume(&mut self, _val: Self::Value) {
@@ -374,7 +378,11 @@ impl<'a, 'tcx> IntrinsicCallMethods<'tcx> for Builder<'a, 'tcx> {
 }
 
 impl Builder<'_, '_> {
-    pub fn abort_with_message(&mut self, message: String) {
+    pub fn abort_with_message_and_debug_printf_args(
+        &mut self,
+        message: String,
+        debug_printf_args: impl IntoIterator<Item = SpirvValue>,
+    ) {
         // FIXME(eddyb) this should be cached more efficiently.
         let void_ty = SpirvType::Void.def(rustc_span::DUMMY_SP, self);
 
@@ -385,6 +393,10 @@ impl Builder<'_, '_> {
             void_ty,
             CustomInst::Abort {
                 message: Operand::IdRef(message_id),
+                debug_printf_args: debug_printf_args
+                    .into_iter()
+                    .map(|arg| Operand::IdRef(arg.def(self)))
+                    .collect(),
             },
         );
         self.unreachable();

crates/rustc_codegen_spirv/src/codegen_cx/constant.rs

@@ -172,12 +172,16 @@ impl<'tcx> ConstMethods<'tcx> for CodegenCx<'tcx> {
         let str_ty = self
             .layout_of(self.tcx.types.str_)
             .spirv_type(DUMMY_SP, self);
-        // FIXME(eddyb) include the actual byte data.
         (
             self.def_constant(
                 self.type_ptr_to(str_ty),
                 SpirvConst::PtrTo {
-                    pointee: self.undef(str_ty).def_cx(self),
+                    pointee: self
+                        .constant_composite(
+                            str_ty,
+                            s.bytes().map(|b| self.const_u8(b).def_cx(self)),
+                        )
+                        .def_cx(self),
                 },
             ),
             self.const_usize(len as u64),

crates/rustc_codegen_spirv/src/custom_insts.rs

@@ -49,9 +49,9 @@ lazy_static! {
 }
 
 macro_rules! def_custom_insts {
-    ($($num:literal => $name:ident $({ $($field:ident),+ $(,)? })?),+ $(,)?) => {
+    ($($num:literal => $name:ident $({ $($field:ident),+ $(, ..$variadic_field:ident)? $(,)? })?),+ $(,)?) => {
         const SCHEMA: &[(u32, &str, &[&str])] = &[
-            $(($num, stringify!($name), &[$($(stringify!($field)),+)?])),+
+            $(($num, stringify!($name), &[$($(stringify!($field),)+ $(stringify!(..$variadic_field),)?)?])),+
         ];
 
         #[repr(u32)]
@@ -74,16 +74,19 @@ macro_rules! def_custom_insts {
             pub fn with_operands<T: Clone>(self, operands: &[T]) -> CustomInst<T> {
                 match self {
                     $(Self::$name => match operands {
-                        [$($($field),+)?] => CustomInst::$name $({ $($field: $field.clone()),+ })?,
+                        [$($($field,)+ $(ref $variadic_field @ ..)?)?] => CustomInst::$name $({
+                            $($field: $field.clone(),)+
+                            $($variadic_field: $variadic_field.iter().cloned().collect())?
+                        })?,
                         _ => unreachable!("{self:?} does not have the right number of operands"),
                     }),+
                 }
             }
         }
 
-        #[derive(Copy, Clone, Debug)]
+        #[derive(Clone, Debug)]
         pub enum CustomInst<T> {
-            $($name $({ $($field: T),+ })?),+
+            $($name $({ $($field: T,)+ $($variadic_field: SmallVec<[T; 4]>)? })?),+
         }
 
         impl<T> CustomInst<T> {
@@ -96,7 +99,9 @@ macro_rules! def_custom_insts {
             // HACK(eddyb) this should return an iterator, but that's too much effort.
             pub fn into_operands(self) -> SmallVec<[T; 8]> {
                 match self {
-                    $(Self::$name $({ $($field),+ })? => [$($($field),+)?].into_iter().collect()),+
+                    $(Self::$name $({ $($field,)+ $($variadic_field)? })? => {
+                        [$($($field),+)?].into_iter() $($(.chain($variadic_field))?)? .collect()
+                    })+
                 }
             }
         }
@@ -146,7 +151,9 @@ def_custom_insts! {
     // users to do `catch_unwind` at the top-level of their shader to handle
     // panics specially (e.g. by appending to a custom buffer, or using some
     // specific color in a fragment shader, to indicate a panic happened).
-    4 => Abort { message },
+    // NOTE(eddyb) the `message` string follows `debugPrintf` rules, with remaining
+    // operands (collected into `debug_printf_args`) being its formatting arguments.
+    4 => Abort { message, ..debug_printf_args },
 }
 
 impl CustomOp {