diff --git a/src/test/codegen/fastcall-inreg.rs b/src/test/codegen/fastcall-inreg.rs
index ec7a679159286..f550ac11f64ae 100644
--- a/src/test/codegen/fastcall-inreg.rs
+++ b/src/test/codegen/fastcall-inreg.rs
@@ -2,7 +2,7 @@
 // as "inreg" like the C/C++ compilers for the platforms.
 // x86 only.
 
-// compile-flags: --target i686-unknown-linux-gnu -C no-prepopulate-passes
+// compile-flags: --target i686-unknown-linux-gnu -O -C no-prepopulate-passes
 // needs-llvm-components: x86
 
 #![crate_type = "lib"]
diff --git a/src/test/codegen/repr-transparent-aggregates-1.rs b/src/test/codegen/repr-transparent-aggregates-1.rs
index a61dad218cd85..4ad3642c03d68 100644
--- a/src/test/codegen/repr-transparent-aggregates-1.rs
+++ b/src/test/codegen/repr-transparent-aggregates-1.rs
@@ -1,4 +1,4 @@
-// compile-flags: -C no-prepopulate-passes
+// compile-flags: -O -C no-prepopulate-passes
 //
 
 // ignore-arm
diff --git a/src/test/codegen/riscv-abi/riscv64-lp64-lp64f-lp64d-abi.rs b/src/test/codegen/riscv-abi/riscv64-lp64-lp64f-lp64d-abi.rs
index c67406ea69338..faf81b5ae7605 100644
--- a/src/test/codegen/riscv-abi/riscv64-lp64-lp64f-lp64d-abi.rs
+++ b/src/test/codegen/riscv-abi/riscv64-lp64-lp64f-lp64d-abi.rs
@@ -1,4 +1,4 @@
-// compile-flags: --target riscv64gc-unknown-linux-gnu -C no-prepopulate-passes
+// compile-flags: --target riscv64gc-unknown-linux-gnu -O -C no-prepopulate-passes
 // needs-llvm-components: riscv
 
 #![crate_type = "lib"]
diff --git a/src/test/codegen/union-abi.rs b/src/test/codegen/union-abi.rs
index bb87d263bdf3d..99576a5f57e90 100644
--- a/src/test/codegen/union-abi.rs
+++ b/src/test/codegen/union-abi.rs
@@ -1,5 +1,5 @@
 // ignore-emscripten vectors passed directly
-// compile-flags: -C no-prepopulate-passes
+// compile-flags: -O -C no-prepopulate-passes
 
 // This test that using union forward the abi of the inner type, as
 // discussed in #54668