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/*========================== begin_copyright_notice ============================
Copyright (C) 2025 Intel Corporation
SPDX-License-Identifier: MIT
============================= end_copyright_notice ===========================*/
#include "Compiler/CISACodeGen/DropTargetBBs.hpp"
#include "common/LLVMWarningsPush.hpp"
#include <llvm/ADT/STLExtras.h>
#include <llvm/IR/Function.h>
#include <llvm/IR/Constants.h>
#include <llvm/IR/Instructions.h>
#include "common/LLVMWarningsPop.hpp"
#include "Compiler/IGCPassSupport.h"
#include "common/igc_regkeys.hpp"
#include <fstream>
#include <string>
#include <optional>
#include <filesystem>
using namespace llvm;
using namespace IGC;
#define PASS_FLAG "igc-drop-target-bbs"
#define PASS_DESCRIPTION "Drop target basic blocks"
#define PASS_CFG_ONLY false
#define PASS_ANALYSIS false
IGC_INITIALIZE_PASS_BEGIN(DropTargetBBs, PASS_FLAG, PASS_DESCRIPTION, PASS_CFG_ONLY, PASS_ANALYSIS)
IGC_INITIALIZE_PASS_END(DropTargetBBs, PASS_FLAG, PASS_DESCRIPTION, PASS_CFG_ONLY, PASS_ANALYSIS)
#define DROP_BB_DEBUG(msg) \
do { \
if (VerboseLog) { \
llvm::errs() << msg << "\n"; \
} \
} while (0)
char IGC::DropTargetBBs::ID = 0;
DropTargetBBs::DropTargetBBs() : FunctionPass(ID), VerboseLog(IGC_GET_FLAG_VALUE(VerboseDropTargetBBs)) {
initializeDropTargetBBsPass(*PassRegistry::getPassRegistry());
}
void DropTargetBBs::getAnalysisUsage(llvm::AnalysisUsage &AU) const {}
static std::optional<int> getBBIndexByName(Function &F, const std::string &BBName) {
int bbIndex = 0;
for (auto &BB : F) {
if (BB.hasName() && BB.getName() == BBName) {
return bbIndex;
}
bbIndex++;
}
return std::nullopt;
}
static std::optional<SmallVector<std::string, 8>> getBBNamesToDrop(const Function &F, const char *DropBBListBasePath) {
SmallVector<std::string, 8> BBsToDrop;
std::filesystem::path DropBBListPath = std::filesystem::path(DropBBListBasePath) / (F.getName().str() + ".txt");
{
std::ifstream DropBBFile(DropBBListPath);
if (!DropBBFile.is_open()) {
return std::nullopt;
}
std::string line;
while (std::getline(DropBBFile, line)) {
if (line.empty()) {
continue;
}
if (line.back() == '\r') {
line.pop_back();
}
BBsToDrop.push_back(line);
}
DropBBFile.close();
}
return BBsToDrop;
}
bool DropTargetBBs::runOnFunction(Function &F) {
if (F.isDeclaration()) {
return false;
}
auto BBsToDropOptional = getBBNamesToDrop(F, IGC_GET_REGKEYSTRING(DropTargetBBListPath));
if (!BBsToDropOptional.has_value()) {
return false;
}
const auto &BBsToDrop = BBsToDropOptional.value();
SmallVector<std::uint32_t, 8> BBIndexesToDrop;
for (const auto &BBName : BBsToDrop) {
auto BBIndex = getBBIndexByName(F, BBName);
if (BBIndex.has_value()) {
BBIndexesToDrop.push_back(BBIndex.value());
}
}
if (BBIndexesToDrop.empty()) {
return false;
}
DROP_BB_DEBUG("DropTargetBBss: Examining function: " << F.getName());
DROP_BB_DEBUG("DropTargetBBss: BB num: " << F.size());
for (const auto &BBIndex : BBIndexesToDrop) {
if (BBIndex >= F.size()) {
continue;
}
auto BI = F.begin();
std::advance(BI, BBIndex);
BasicBlock *BB = &*BI;
DROP_BB_DEBUG("DropTargetBBs: Dropping BB index: " << BBIndex << " Name: " << BB->getName());
while (!BB->use_empty()) {
auto *User = *BB->user_begin();
if (auto *PHI = dyn_cast<PHINode>(User)) {
PHI->removeIncomingValue(BB, true);
} else if (auto *Br = dyn_cast<BranchInst>(User)) {
BasicBlock *NextBB = BB->getNextNode();
if (NextBB) {
Br->setSuccessor(Br->getSuccessor(0) == BB ? 0 : 1, NextBB);
} else {
Br->eraseFromParent();
}
} else if (auto *SI = dyn_cast<SwitchInst>(User)) {
if (auto *CI = SI->findCaseDest(BB)) {
SI->removeCase(SI->findCaseValue(CI));
}
} else {
User->replaceUsesOfWith(BB, PoisonValue::get(BB->getType()));
}
}
for (Instruction &I : *BB) {
if (!I.use_empty()) {
I.replaceAllUsesWith(PoisonValue::get(I.getType()));
}
}
BB->eraseFromParent();
}
return true;
}
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