[llvm-branch-commits] [llvm] [AMDGPU] Push amdgpu-preload-kern-arg-prolog after livedebugvalues (PR #126148)

[Scott Linder via llvm-branch-commits]

https://github.com/slinder1 created https://github.com/llvm/llvm-project/pull/126148

This is effectively a workaround for a bug in livedebugvalues, but seems
to potentially be a general improvement, as BB sections seems like it
could ruin the special 256-byte prelude scheme that
amdgpu-preload-kern-arg-prolog requires anyway. Moving it even later
doesn't seem to have any material impact, and just adds livedebugvalues
to the list of things which no longer have to deal with pseudo
multiple-entry functions.

AMDGPU debug-info isn't supported upstream yet, so the bug being avoided
isn't testable here. I am posting the patch upstream to avoid an
unnecessary diff with AMD's fork.

>From bcb8f4adb9af074b91bc85a726883a2e114d33d4 Mon Sep 17 00:00:00 2001
From: Scott Linder <Scott.Linder at amd.com>
Date: Thu, 6 Feb 2025 00:01:07 +0000
Subject: [PATCH] [AMDGPU] Push amdgpu-preload-kern-arg-prolog after
 livedebugvalues

This is effectively a workaround for a bug in livedebugvalues, but seems
to potentially be a general improvement, as BB sections seems like it
could ruin the special 256-byte prelude scheme that
amdgpu-preload-kern-arg-prolog requires anyway. Moving it even later
doesn't seem to have any material impact, and just adds livedebugvalues
to the list of things which no longer have to deal with pseudo
multiple-entry functions.

AMDGPU debug-info isn't supported upstream yet, so the bug being avoided
isn't testable here. I am posting the patch upstream to avoid an
unnecessary diff with AMD's fork.
---
 llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.cpp | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.cpp b/llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.cpp
index fffd30b26dc1d50..67b155e4e740011 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.cpp
@@ -1147,6 +1147,7 @@ class GCNPassConfig final : public AMDGPUPassConfig {
   void addPostRegAlloc() override;
   void addPreSched2() override;
   void addPreEmitPass() override;
+  void addPostBBSections() override;
 };
 
 } // end anonymous namespace
@@ -1686,6 +1687,11 @@ void GCNPassConfig::addPreEmitPass() {
     addPass(&AMDGPUInsertDelayAluID);
 
   addPass(&BranchRelaxationPassID);
+}
+
+void GCNPassConfig::addPostBBSections() {
+  // We run this later to avoid passes like livedebugvalues and BBSections
+  // having to deal with the apparent multi-entry functions we may generate.
   addPass(createAMDGPUPreloadKernArgPrologLegacyPass());
 }