[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.

Author: slinder1

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());
 }
 

llvm/test/CodeGen/AMDGPU/llc-pipeline.ll

@@ -145,11 +145,11 @@
 ; GCN-O0-NEXT:        Post RA hazard recognizer
 ; GCN-O0-NEXT:        AMDGPU Insert waits for SGPR read hazards
 ; GCN-O0-NEXT:        Branch relaxation pass
-; GCN-O0-NEXT:        AMDGPU Preload Kernel Arguments Prolog
 ; GCN-O0-NEXT:        Register Usage Information Collector Pass
 ; GCN-O0-NEXT:        Remove Loads Into Fake Uses
 ; GCN-O0-NEXT:        Live DEBUG_VALUE analysis
 ; GCN-O0-NEXT:        Machine Sanitizer Binary Metadata
+; GCN-O0-NEXT:        AMDGPU Preload Kernel Arguments Prolog
 ; GCN-O0-NEXT:        Lazy Machine Block Frequency Analysis
 ; GCN-O0-NEXT:        Machine Optimization Remark Emitter
 ; GCN-O0-NEXT:        Stack Frame Layout Analysis
@@ -430,11 +430,11 @@
 ; GCN-O1-NEXT:        AMDGPU Insert waits for SGPR read hazards
 ; GCN-O1-NEXT:        AMDGPU Insert Delay ALU
 ; GCN-O1-NEXT:        Branch relaxation pass
-; GCN-O1-NEXT:        AMDGPU Preload Kernel Arguments Prolog
 ; GCN-O1-NEXT:        Register Usage Information Collector Pass
 ; GCN-O1-NEXT:        Remove Loads Into Fake Uses
 ; GCN-O1-NEXT:        Live DEBUG_VALUE analysis
 ; GCN-O1-NEXT:        Machine Sanitizer Binary Metadata
+; GCN-O1-NEXT:        AMDGPU Preload Kernel Arguments Prolog
 ; GCN-O1-NEXT:        Lazy Machine Block Frequency Analysis
 ; GCN-O1-NEXT:        Machine Optimization Remark Emitter
 ; GCN-O1-NEXT:        Stack Frame Layout Analysis
@@ -743,11 +743,11 @@
 ; GCN-O1-OPTS-NEXT:        AMDGPU Insert waits for SGPR read hazards
 ; GCN-O1-OPTS-NEXT:        AMDGPU Insert Delay ALU
 ; GCN-O1-OPTS-NEXT:        Branch relaxation pass
-; GCN-O1-OPTS-NEXT:        AMDGPU Preload Kernel Arguments Prolog
 ; GCN-O1-OPTS-NEXT:        Register Usage Information Collector Pass
 ; GCN-O1-OPTS-NEXT:        Remove Loads Into Fake Uses
 ; GCN-O1-OPTS-NEXT:        Live DEBUG_VALUE analysis
 ; GCN-O1-OPTS-NEXT:        Machine Sanitizer Binary Metadata
+; GCN-O1-OPTS-NEXT:        AMDGPU Preload Kernel Arguments Prolog
 ; GCN-O1-OPTS-NEXT:        Lazy Machine Block Frequency Analysis
 ; GCN-O1-OPTS-NEXT:        Machine Optimization Remark Emitter
 ; GCN-O1-OPTS-NEXT:        Stack Frame Layout Analysis
@@ -1062,11 +1062,11 @@
 ; GCN-O2-NEXT:        AMDGPU Insert waits for SGPR read hazards
 ; GCN-O2-NEXT:        AMDGPU Insert Delay ALU
 ; GCN-O2-NEXT:        Branch relaxation pass
-; GCN-O2-NEXT:        AMDGPU Preload Kernel Arguments Prolog
 ; GCN-O2-NEXT:        Register Usage Information Collector Pass
 ; GCN-O2-NEXT:        Remove Loads Into Fake Uses
 ; GCN-O2-NEXT:        Live DEBUG_VALUE analysis
 ; GCN-O2-NEXT:        Machine Sanitizer Binary Metadata
+; GCN-O2-NEXT:        AMDGPU Preload Kernel Arguments Prolog
 ; GCN-O2-NEXT:        Lazy Machine Block Frequency Analysis
 ; GCN-O2-NEXT:        Machine Optimization Remark Emitter
 ; GCN-O2-NEXT:        Stack Frame Layout Analysis
@@ -1394,11 +1394,11 @@
 ; GCN-O3-NEXT:        AMDGPU Insert waits for SGPR read hazards
 ; GCN-O3-NEXT:        AMDGPU Insert Delay ALU
 ; GCN-O3-NEXT:        Branch relaxation pass
-; GCN-O3-NEXT:        AMDGPU Preload Kernel Arguments Prolog
 ; GCN-O3-NEXT:        Register Usage Information Collector Pass
 ; GCN-O3-NEXT:        Remove Loads Into Fake Uses
 ; GCN-O3-NEXT:        Live DEBUG_VALUE analysis
 ; GCN-O3-NEXT:        Machine Sanitizer Binary Metadata
+; GCN-O3-NEXT:        AMDGPU Preload Kernel Arguments Prolog
 ; GCN-O3-NEXT:        Lazy Machine Block Frequency Analysis
 ; GCN-O3-NEXT:        Machine Optimization Remark Emitter
 ; GCN-O3-NEXT:        Stack Frame Layout Analysis