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/*========================== begin_copyright_notice ============================
Copyright (C) 2025 Intel Corporation
SPDX-License-Identifier: MIT
============================= end_copyright_notice ===========================*/
#include "SinkPointerConstAdd.h"
#include "common/LLVMWarningsPush.hpp"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/IRBuilder.h"
#include "common/LLVMWarningsPop.hpp"
// Simple pass which sinks constant add operations in pointer calculations
// It changes following pattern:
// %addr_part1 = <base1> + const
// %addr_part2 = <base2> + %addr_part1
// %ptr = inttoptr %addr_part2
// to:
// %addr_part1 = <base1> + <base2>
// %addr_part2 = <addr_part1> + const
// %ptr = inttoptr %addr_part2
// This helps other optimizations like GVN to eliminate redundant calculations.
using namespace llvm;
class SinkPointerConstAddPass : public llvm::FunctionPass {
public:
SinkPointerConstAddPass() : llvm::FunctionPass(ID) {
initializeSinkPointerConstAddPassPass(*llvm::PassRegistry::getPassRegistry());
}
virtual bool runOnFunction(llvm::Function &F) override;
virtual void getAnalysisUsage(llvm::AnalysisUsage &AU) const override { AU.setPreservesCFG(); }
virtual llvm::StringRef getPassName() const override { return "SinkPointerConstAdd"; }
static char ID;
private:
bool getConstantOffset(llvm::Value *value, int &offset);
};
#define PASS_FLAG "igc-sink-ptr-const-add"
#define PASS_DESCRIPTION "Sink pointer const add"
#define PASS_CFG_ONLY false
#define PASS_ANALYSIS false
IGC_INITIALIZE_PASS(SinkPointerConstAddPass, PASS_FLAG, PASS_DESCRIPTION, PASS_CFG_ONLY, PASS_ANALYSIS)
bool SinkPointerConstAddPass::getConstantOffset(llvm::Value *value, int &offset) {
// Recursively search for constant add operations - this will stop after the first const add found,
// and should be called repeatedly until no more const adds can be sunk.
if (value->getNumUses() > 1) {
return false; // We cannot sink constant add if the value is used more than once.
}
if (llvm::Instruction *instr = llvm::dyn_cast<llvm::Instruction>(value)) {
if (instr->getOpcode() == llvm::Instruction::Trunc || instr->getOpcode() == llvm::Instruction::ZExt ||
instr->getOpcode() == llvm::Instruction::SExt) {
// Skip cast instructions
llvm::Instruction *op = llvm::dyn_cast<llvm::Instruction>(instr->getOperand(0));
// This is a simple pass, only sink within the same basic block
if (op && instr->getParent() == op->getParent()) {
return getConstantOffset(instr->getOperand(0), offset);
} else {
return false;
}
} else if (instr->getOpcode() == llvm::Instruction::Add || instr->getOpcode() == llvm::Instruction::Sub) {
if (llvm::ConstantInt *constInt = llvm::dyn_cast<llvm::ConstantInt>(instr->getOperand(1))) {
offset = instr->getOpcode() == llvm::Instruction::Add ? offset + constInt->getSExtValue()
: offset - constInt->getSExtValue();
instr->replaceAllUsesWith(instr->getOperand(0));
instr->eraseFromParent();
return true;
} else if (llvm::ConstantInt *constInt = llvm::dyn_cast<llvm::ConstantInt>(instr->getOperand(0))) {
if (instr->getOpcode() == llvm::Instruction::Sub) {
// Cannot sink constant on the left side of subtraction
return false;
}
offset += constInt->getSExtValue();
instr->replaceAllUsesWith(instr->getOperand(1));
instr->eraseFromParent();
return true;
} else {
llvm::Instruction *op0 = llvm::dyn_cast<llvm::Instruction>(instr->getOperand(0));
llvm::Instruction *op1 = llvm::dyn_cast<llvm::Instruction>(instr->getOperand(1));
// This is a simple pass, only sink within the same basic block
return (op0 && instr->getParent() == op0->getParent() && getConstantOffset(op0, offset)) ? true
: (op1 && instr->getParent() == op1->getParent()) ? getConstantOffset(op1, offset)
: false;
}
}
}
return false;
}
bool SinkPointerConstAddPass::runOnFunction(llvm::Function &F) {
bool changed = false;
std::vector<llvm::IntToPtrInst *> intToPtrInsts;
intToPtrInsts.reserve(50);
// Collect all inttoptr instructions first
for (llvm::BasicBlock &BB : F) {
for (llvm::Instruction &inst : BB) {
if (llvm::IntToPtrInst *intrinsic = llvm::dyn_cast<llvm::IntToPtrInst>(&inst)) {
intToPtrInsts.push_back(intrinsic);
}
}
}
for (auto &intrinsic : intToPtrInsts) {
int offset = 0;
// Keep sinking constant adds until no more can be sunk
while (getConstantOffset(intrinsic->getOperand(0), offset)) {
changed = true;
}
// If we found any constant offset, create new pointer calculation
if (offset != 0) {
llvm::IRBuilder<> builder(intrinsic);
llvm::Value *newPtr =
builder.CreateIntToPtr(builder.CreateAdd(intrinsic->getOperand(0),
llvm::ConstantInt::get(intrinsic->getOperand(0)->getType(), offset)),
intrinsic->getType());
intrinsic->replaceAllUsesWith(newPtr);
intrinsic->eraseFromParent();
}
}
return changed;
}
char SinkPointerConstAddPass::ID = 0;
llvm::FunctionPass *createSinkPointerConstAddPass() { return new SinkPointerConstAddPass(); }
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