[llvm] Add a pass "SinkGEPConstOffset" (PR #140657)

[via llvm-commits]

================
@@ -0,0 +1,260 @@
+//===- SinkGEPConstOffset.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
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Scalar/SinkGEPConstOffset.h"
+#include "llvm/ADT/APInt.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/DepthFirstIterator.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/MemoryBuiltins.h"
+#include "llvm/Analysis/TargetLibraryInfo.h"
+#include "llvm/Analysis/TargetTransformInfo.h"
+#include "llvm/Analysis/ValueTracking.h"
+#include "llvm/IR/BasicBlock.h"
+#include "llvm/IR/Constant.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/DataLayout.h"
+#include "llvm/IR/DerivedTypes.h"
+#include "llvm/IR/Dominators.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/GetElementPtrTypeIterator.h"
+#include "llvm/IR/IRBuilder.h"
+#include "llvm/IR/InstrTypes.h"
+#include "llvm/IR/Instruction.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/Module.h"
+#include "llvm/IR/PassManager.h"
+#include "llvm/IR/PatternMatch.h"
+#include "llvm/IR/Type.h"
+#include "llvm/IR/User.h"
+#include "llvm/IR/Value.h"
+#include "llvm/InitializePasses.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/Casting.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/Transforms/Utils/Local.h"
+#include <cassert>
+#include <cstdint>
+#include <string>
+
+using namespace llvm;
+using namespace llvm::PatternMatch;
+
+static cl::opt<bool> DisableSinkGEPConstOffset(
+    "disable-sink-gep-const-offset", cl::init(false),
+    cl::desc("Do not sink the constant offset from a GEP instruction"),
+    cl::Hidden);
+
+namespace {
+
+/// A pass that tries to sink const offset in GEP chain to tail.
+/// It is a FunctionPass because searching for the constant offset may inspect
+/// other basic blocks.
+class SinkGEPConstOffsetLegacyPass : public FunctionPass {
+public:
+  static char ID;
+
+  SinkGEPConstOffsetLegacyPass() : FunctionPass(ID) {
+    initializeSinkGEPConstOffsetLegacyPassPass(
+        *PassRegistry::getPassRegistry());
+  }
+
+  void getAnalysisUsage(AnalysisUsage &AU) const override {
+    AU.setPreservesCFG();
+  }
+
+  bool runOnFunction(Function &F) override;
+};
+
+/// A pass that tries to sink const offset in GEP chain to tail.
+/// It is a FunctionPass because searching for the constant offset may inspect
+/// other basic blocks.
+class SinkGEPConstOffset {
+public:
+  SinkGEPConstOffset() {}
+
+  bool run(Function &F);
+
+private:
+  /// Sink constant offset in a GEP chain to tail. For example,
+  /// %gep0 = getelementptr half, ptr addrspace(3) %ptr, i32 512
+  /// %gep1 = getelementptr half, ptr addrspace(3) %gep0, i32 %ofst0
+  /// %gep2 = getelementptr half, ptr addrspace(3) %gep1, i32 %ofst1
+  /// %data = load half, ptr addrspace(3) %gep2, align 2
+  /// ==>
+  /// %gep0 = getelementptr half, ptr addrspace(3) %ptr, i32 %ofst0
+  /// %gep1 = getelementptr half, ptr addrspace(3) %gep0, i32 %ofst1
+  /// %gep2 = getelementptr half, ptr addrspace(3) %gep1, i32 512
+  /// %data = load half, ptr addrspace(3) %gep2, align 2
+  ///
+  /// Return true if Ptr is a candidate for upper GEP in recursive calling.
+  bool sinkGEPConstantOffset(Value *Ptr, bool &Changed);
----------------
StevenYangCC wrote:

The return value doesn't mean the same thing as Changed.

https://github.com/llvm/llvm-project/pull/140657