MC,AMDGPU: Don't pad .text with s_code_end if it would otherwise be empty

[trenouf]

We don't want that padding in a module that only contains data, not code.

Also fix MCSection::hasInstructions() so it works with the asm streamer too.

[llvmbot]

@llvm/pr-subscribers-mc

@llvm/pr-subscribers-backend-amdgpu

Author: Tim Renouf (trenouf)

Changes

We don't want that padding in a module that only contains data, not code.

---

Full diff: https://github.com/llvm/llvm-project/pull/147980.diff

1 Files Affected:

• (modified) llvm/lib/Target/AMDGPU/AMDGPUAsmPrinter.cpp (+3-1)

diff --git a/llvm/lib/Target/AMDGPU/AMDGPUAsmPrinter.cpp b/llvm/lib/Target/AMDGPU/AMDGPUAsmPrinter.cpp
index 749b9efc81378..3765c1d2b106c 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPUAsmPrinter.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPUAsmPrinter.cpp
@@ -486,10 +486,12 @@ bool AMDGPUAsmPrinter::doFinalization(Module &M) {
   // Pad with s_code_end to help tools and guard against instruction prefetch
   // causing stale data in caches. Arguably this should be done by the linker,
   // which is why this isn't done for Mesa.
+  // Don't do it if there are no functions.
   const MCSubtargetInfo &STI = *getGlobalSTI();
   if ((AMDGPU::isGFX10Plus(STI) || AMDGPU::isGFX90A(STI)) &&
       (STI.getTargetTriple().getOS() == Triple::AMDHSA ||
-       STI.getTargetTriple().getOS() == Triple::AMDPAL)) {
+       STI.getTargetTriple().getOS() == Triple::AMDPAL) &&
+      !M.empty()) {
     OutStreamer->switchSection(getObjFileLowering().getTextSection());
     getTargetStreamer()->EmitCodeEnd(STI);
   }

[arsenm]

Testcase?

[jayfoad]

Seems reasonable but I wonder if there's a better way to test "did we emit any code?". E.g. what if the module contains some function declarations but no definitions?

[arsenm]

Plus this may misdetect available_externally functions which will be dropped

[trenouf]

I changed to using MCSection::hasInstructions(), which I had to fix to work with the asm streamer.

Also added test. The positive case (when it does add padding) already has a test.