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/*========================== begin_copyright_notice ============================
Copyright (C) 2022-2023 Intel Corporation
SPDX-License-Identifier: MIT
============================= end_copyright_notice ===========================*/
//===----------------------------------------------------------------------===//
//
// The purpose of this pass is to add a limit for each loop,
// so no infinite loops occur.
//===----------------------------------------------------------------------===//
#include <vector>
#include <set>
#include "CapLoopIterationsPass.h"
#include "IGCIRBuilder.h"
#include "Compiler/IGCPassSupport.h"
#include "common/LLVMWarningsPush.hpp"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/IR/Dominators.h"
#include "common/LLVMWarningsPop.hpp"
using namespace llvm;
using namespace IGC;
// Register pass to igc-opt
#define PASS_FLAG "cap-loop-iterations-pass"
#define PASS_DESCRIPTION "Limit the number of iterations in each loop to UINT_MAX. Prevents inifinite loops"
#define PASS_CFG_ONLY false
#define PASS_ANALYSIS false
IGC_INITIALIZE_PASS_BEGIN(CapLoopIterations, PASS_FLAG, PASS_DESCRIPTION, PASS_CFG_ONLY, PASS_ANALYSIS)
IGC_INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
IGC_INITIALIZE_PASS_END(CapLoopIterations, PASS_FLAG, PASS_DESCRIPTION, PASS_CFG_ONLY, PASS_ANALYSIS)
char CapLoopIterations::ID = 0;
CapLoopIterations::CapLoopIterations() : FunctionPass(ID), m_iterationLimit(UINT_MAX)
{
initializeCapLoopIterationsPass(*PassRegistry::getPassRegistry());
}
CapLoopIterations::CapLoopIterations(uint32_t iterationLimit) : FunctionPass(ID), m_iterationLimit(iterationLimit)
{
initializeCapLoopIterationsPass(*PassRegistry::getPassRegistry());
}
void CapLoopIterations::getAnalysisUsage(llvm::AnalysisUsage& AU) const
{
AU.addRequired<LoopInfoWrapperPass>();
}
bool CapLoopIterations::runOnFunction(Function& F)
{
auto changed = false;
auto& loopInfo = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
auto IRB = IRBuilder(F.getContext());
for (auto loop : loopInfo.getLoopsInPreorder())
{
if (!loop->isLoopSimplifyForm()) // preheader is required
continue;
IRB.SetInsertPoint(loop->getHeader()->getFirstNonPHI());
auto counterphi = IRB.CreatePHI(IRB.getInt32Ty(), 2, "counterphi");
counterphi->addIncoming(IRB.getInt32(0), loop->getLoopPreheader());
auto counter = IRB.CreateAdd(counterphi, IRB.getInt32(1), "counter");
counterphi->addIncoming(counter, loop->getLoopLatch());
auto forceexit = IRB.CreateICmpEQ(counter, IRB.getInt32(m_iterationLimit), "forceloopexit");
llvm::SmallVector<std::pair<BasicBlock*, BasicBlock*>, 4> exitedges;
loop->getExitEdges(exitedges);
for (const auto& [exitingbb, exitbb] : exitedges)
{
if (auto br = dyn_cast<BranchInst>(exitingbb->getTerminator()))
{
if (!br->isConditional())
continue;
IRB.SetInsertPoint(br);
if (br->getSuccessor(0) == exitbb) // br i1 %cond, %exit, %notexit
{
br->setCondition(
IRB.CreateOr(forceexit, br->getCondition())
);
}
else // br i1 %cond, %notexit, %exit
{
br->setCondition(
IRB.CreateAnd(IRB.CreateNot(forceexit), br->getCondition())
);
}
}
}
changed = true;
}
return changed;
}
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