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Spurious errors emitted for global-scope asm with ThinLTO #61991

Open Amanieu opened 1 year ago

Amanieu commented 1 year ago

test.c

asm("fld f0, 0(sp)");

Output

$ clang test.c -c -target riscv64-unknown-linux-gnu -flto=thin
error: instruction requires the following: 'D' (Double-Precision Floating-Point)
fld f0, 0(sp)
^
error: instruction requires the following: 'D' (Double-Precision Floating-Point)
fld f0, 0(sp)
^

The D feature is enabled by default on riscv64-unknown-linux-gnu, so this error should normally not be emitted.

However compilation still completes successfully (exit code 0) and produces valid LLVM bitcode in test.o.

Similar bug in rustc: https://github.com/rust-lang/rust/issues/80608

llvmbot commented 1 year ago

@llvm/issue-subscribers-backend-risc-v

Dirbaio commented 3 months ago

I'm trying to fix this issue and https://github.com/rust-lang/rust/issues/80608 https://github.com/rust-lang/rust/issues/127269 which I believe have the same root cause.

So far I've narrowed it down to here https://github.com/llvm/llvm-project/blob/main/llvm/lib/Object/ModuleSymbolTable.cpp#L96

it creates an ASM parser with empty ("") target features, so parsing the ASM fails. The target requires "+vfp3d16" for target features. I've confirmed if I hardcode that in there the error goes away. However, I don't know what the right fix would be. How can I obtain the target features from there? The module only contains the target triple.

Any hints would be appreciated.

jamesmunns commented 3 months ago

Also noting from the other thread: this appears not JUST to be a RISC-V relevant issue, it's applicable to any target that requires target features. The issue linked in https://github.com/rust-lang/rust/issues/127269 is for an Arm Cortex-R processor.