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//===------------------------------------------------------------*- C++ -*-===//
//
// 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/DropUnnecessaryAssumes.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/Transforms/Utils/Local.h"
using namespace llvm;
using namespace llvm::PatternMatch;
PreservedAnalyses
DropUnnecessaryAssumesPass::run(Function &F, FunctionAnalysisManager &FAM) {
AssumptionCache &AC = FAM.getResult<AssumptionAnalysis>(F);
bool Changed = false;
for (AssumptionCache::ResultElem &Elem : AC.assumptions()) {
auto *Assume = cast_or_null<AssumeInst>(Elem.Assume);
if (!Assume)
continue;
// TODO: Handle assumes with operand bundles.
if (Assume->hasOperandBundles())
continue;
Value *Cond = Assume->getArgOperand(0);
// Don't drop type tests, which have special semantics.
if (match(Cond, m_Intrinsic<Intrinsic::type_test>()))
continue;
SmallPtrSet<Value *, 8> Affected;
findValuesAffectedByCondition(Cond, /*IsAssume=*/true,
[&](Value *A) { Affected.insert(A); });
// If all the affected uses have only one use (part of the assume), then
// the assume does not provide useful information. Note that additional
// users may appear as a result of inlining and CSE, so we should only
// make this assumption late in the optimization pipeline.
// TODO: Handle dead cyclic usages.
// TODO: Handle multiple dead assumes on the same value.
if (!all_of(Affected, match_fn(m_OneUse(m_Value()))))
continue;
Assume->eraseFromParent();
RecursivelyDeleteTriviallyDeadInstructions(Cond);
Changed = true;
}
if (Changed) {
PreservedAnalyses PA;
PA.preserveSet<CFGAnalyses>();
return PA;
}
return PreservedAnalyses::all();
}
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