AMDGPU/NewPM: Start implementing addCodeGenPrepare (#102816)

Author: arsenm

llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.cpp

@@ -73,6 +73,7 @@
 #include "llvm/Transforms/Utils.h"
 #include "llvm/Transforms/Utils/FixIrreducible.h"
 #include "llvm/Transforms/Utils/LCSSA.h"
+#include "llvm/Transforms/Utils/LowerSwitch.h"
 #include "llvm/Transforms/Utils/SimplifyLibCalls.h"
 #include "llvm/Transforms/Utils/UnifyLoopExits.h"
 #include "llvm/Transforms/Vectorize/LoadStoreVectorizer.h"
@@ -1768,6 +1769,16 @@ AMDGPUCodeGenPassBuilder::AMDGPUCodeGenPassBuilder(
               ShadowStackGCLoweringPass>();
 }
 
+void AMDGPUCodeGenPassBuilder::addCodeGenPrepare(AddIRPass &addPass) const {
+  Base::addCodeGenPrepare(addPass);
+
+  // LowerSwitch pass may introduce unreachable blocks that can cause unexpected
+  // behavior for subsequent passes. Placing it here seems better that these
+  // blocks would get cleaned up by UnreachableBlockElim inserted next in the
+  // pass flow.
+  addPass(LowerSwitchPass());
+}
+
 void AMDGPUCodeGenPassBuilder::addPreISel(AddIRPass &addPass) const {
   const bool LateCFGStructurize = AMDGPUTargetMachine::EnableLateStructurizeCFG;
   const bool DisableStructurizer = AMDGPUTargetMachine::DisableStructurizer;

llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.h

@@ -165,11 +165,14 @@ class AMDGPUPassConfig : public TargetPassConfig {
 
 class AMDGPUCodeGenPassBuilder
     : public CodeGenPassBuilder<AMDGPUCodeGenPassBuilder, GCNTargetMachine> {
+  using Base = CodeGenPassBuilder<AMDGPUCodeGenPassBuilder, GCNTargetMachine>;
+
 public:
   AMDGPUCodeGenPassBuilder(GCNTargetMachine &TM,
                            const CGPassBuilderOption &Opts,
                            PassInstrumentationCallbacks *PIC);
 
+  void addCodeGenPrepare(AddIRPass &) const;
   void addPreISel(AddIRPass &addPass) const;
   void addAsmPrinter(AddMachinePass &, CreateMCStreamer) const;
   Error addInstSelector(AddMachinePass &) const;