[llvm] [WIP][AMDGPU] combine uniform AMDGPU lane Intrinsics (PR #116953)

[Jay Foad via llvm-commits]

================
@@ -0,0 +1,166 @@
+//===-- AMDGPUUniformIntrinsicCombine.cpp ---------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+/// \file
+/// This pass combines uniform intrinsic instructions.
+/// Uniform Intrinsic Combine uses pattern match to identify and optimize
+/// redundant intrinsic instructions.
+//===----------------------------------------------------------------------===//
+
+#include "AMDGPU.h"
+#include "GCNSubtarget.h"
+#include "llvm/Analysis/DomTreeUpdater.h"
+#include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/ScalarEvolution.h"
+#include "llvm/Analysis/TargetLibraryInfo.h"
+#include "llvm/Analysis/UniformityAnalysis.h"
+#include "llvm/CodeGen/TargetPassConfig.h"
+#include "llvm/IR/IRBuilder.h"
+#include "llvm/IR/InstVisitor.h"
+#include "llvm/IR/IntrinsicsAMDGPU.h"
+#include "llvm/IR/PatternMatch.h"
+#include "llvm/InitializePasses.h"
+#include "llvm/Target/TargetMachine.h"
+#include "llvm/Transforms/Utils/BasicBlockUtils.h"
+
+#define DEBUG_TYPE "amdgpu-uniform-intrinsic-combine"
+
+using namespace llvm;
+using namespace llvm::AMDGPU;
+using namespace llvm::PatternMatch;
+
+namespace {
+
+class AMDGPUUniformIntrinsicCombine : public FunctionPass {
+public:
+  static char ID;
+  AMDGPUUniformIntrinsicCombine() : FunctionPass(ID) {}
+
+  bool runOnFunction(Function &F) override;
+
+  void getAnalysisUsage(AnalysisUsage &AU) const override {
+    AU.setPreservesCFG();
+    AU.addRequired<UniformityInfoWrapperPass>();
+    AU.addRequired<TargetPassConfig>();
+  }
+};
+
+class AMDGPUUniformIntrinsicCombineImpl
+    : public InstVisitor<AMDGPUUniformIntrinsicCombineImpl> {
+private:
+  const UniformityInfo *UI;
+
+  bool optimizeUniformIntrinsicInst(IntrinsicInst &II) const;
+
+public:
+  AMDGPUUniformIntrinsicCombineImpl() = delete;
+
+  AMDGPUUniformIntrinsicCombineImpl(const UniformityInfo *UI) : UI(UI) {}
+
+  bool run(Function &F);
+};
+
+} // namespace
+
+char AMDGPUUniformIntrinsicCombine::ID = 0;
+
+char &llvm::AMDGPUUniformIntrinsicCombineID = AMDGPUUniformIntrinsicCombine::ID;
+
+bool AMDGPUUniformIntrinsicCombine::runOnFunction(Function &F) {
+  if (skipFunction(F)) {
+    return false;
+  }
+
+  const UniformityInfo *UI =
+      &getAnalysis<UniformityInfoWrapperPass>().getUniformityInfo();
+
+  return AMDGPUUniformIntrinsicCombineImpl(UI).run(F);
+}
+
+PreservedAnalyses
+AMDGPUUniformIntrinsicCombinePass::run(Function &F,
+                                       FunctionAnalysisManager &AM) {
+
+  const auto *UI = &AM.getResult<UniformityInfoAnalysis>(F);
+
+  bool IsChanged = AMDGPUUniformIntrinsicCombineImpl(UI).run(F);
+
+  if (!IsChanged) {
+    return PreservedAnalyses::all();
+  }
+
+  PreservedAnalyses PA;
+  PA.preserve<DominatorTreeAnalysis>();
+  PA.preserve<LoopAnalysis>();
+  PA.preserve<ScalarEvolutionAnalysis>();
+  PA.preserve<UniformityInfoAnalysis>();
+  PA.preserve<TargetLibraryAnalysis>();
+  return PA;
+}
+
+bool AMDGPUUniformIntrinsicCombineImpl::run(Function &F) {
+
+  bool IsChanged{false};
+
+  // Iterate over each instruction in the function to get the desired intrinsic
+  // inst to check for optimization.
+  for (BasicBlock &BB : F) {
+    for (Instruction &I : BB) {
+      if (auto *Call = dyn_cast<CallInst>(&I)) {
+        if (auto *Intrinsic = dyn_cast<IntrinsicInst>(Call)) {
+          IsChanged |= optimizeUniformIntrinsicInst(*Intrinsic);
+        }
+      }
+    }
+  }
+
+  return IsChanged;
+}
+
+bool AMDGPUUniformIntrinsicCombineImpl::optimizeUniformIntrinsicInst(
+    IntrinsicInst &II) const {
+  llvm::Intrinsic::ID IID = II.getIntrinsicID();
+
+  switch (IID) {
+  case Intrinsic::amdgcn_permlane64:
+  case Intrinsic::amdgcn_readfirstlane:
+  case Intrinsic::amdgcn_readlane: {
+    Value *Src = II.getArgOperand(0);
+    // The below part may not be safe if the exec is not same between the def
+    // and use. Is this part stilll required??
----------------
jayfoad wrote:

No it is not required, now that you pass a Use into isUniform.

https://github.com/llvm/llvm-project/pull/116953