[llvm] AMDGPU/NewPM: Start implementing addCodeGenPrepare (PR #102816)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm updated https://github.com/llvm/llvm-project/pull/102816

>From 2e1ba12bc5f6761867fbd61c152a57a14d774a37 Mon Sep 17 00:00:00 2001
From: Matt Arsenault <Matthew.Arsenault at amd.com>
Date: Sun, 11 Aug 2024 18:20:23 +0400
Subject: [PATCH] AMDGPU/NewPM: Start implementing addCodeGenPrepare

---
 llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.cpp | 11 +++++++++++
 llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.h   |  3 +++
 2 files changed, 14 insertions(+)

diff --git a/llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.cpp b/llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.cpp
index f15d02ac9301e..04b96a32a8970 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.cpp
+++ b/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;
diff --git a/llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.h b/llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.h
index 4dffddd2d44cc..576bf40e3328d 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.h
+++ b/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;