#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/DebugInfoMetadata.h"
+#include "llvm/IR/Dominators.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/InstIterator.h"
#include "llvm/IR/Instructions.h"
class AggressiveDeadCodeElimination {
Function &F;
+
+ // ADCE does not use DominatorTree per se, but it updates it to preserve the
+ // analysis.
+ DominatorTree &DT;
PostDominatorTree &PDT;
/// Mapping of blocks to associated information, an element in BlockInfoVec.
void makeUnconditional(BasicBlock *BB, BasicBlock *Target);
public:
- AggressiveDeadCodeElimination(Function &F, PostDominatorTree &PDT)
- : F(F), PDT(PDT) {}
- bool performDeadCodeElimination();
+ AggressiveDeadCodeElimination(Function &F, DominatorTree &DT,
+ PostDominatorTree &PDT)
+ : F(F), DT(DT), PDT(PDT) {}
+ bool performDeadCodeElimination();
};
}
}
assert((PreferredSucc && PreferredSucc->PostOrder > 0) &&
"Failed to find safe successor for dead branch");
+
+ // Collect removed successors to update the (Post)DominatorTrees.
+ SmallPtrSet<BasicBlock *, 4> RemovedSuccessors;
bool First = true;
for (auto *Succ : successors(BB)) {
- if (!First || Succ != PreferredSucc->BB)
+ if (!First || Succ != PreferredSucc->BB) {
Succ->removePredecessor(BB);
- else
+ RemovedSuccessors.insert(Succ);
+ } else
First = false;
}
makeUnconditional(BB, PreferredSucc->BB);
+
+ // Inform the dominators about the deleted CFG edges.
+ for (auto *Succ : RemovedSuccessors) {
+ // It might have happened that the same successor appeared multiple times
+ // and the CFG edge wasn't really removed.
+ if (Succ != PreferredSucc->BB) {
+ DEBUG(dbgs() << "ADCE: Removing (Post)DomTree edge " << BB->getName()
+ << " -> " << Succ->getName() << "\n");
+ DT.deleteEdge(BB, Succ);
+ PDT.deleteEdge(BB, Succ);
+ }
+ }
+
NumBranchesRemoved += 1;
}
}
InstInfo[NewTerm].Live = true;
if (const DILocation *DL = PredTerm->getDebugLoc())
NewTerm->setDebugLoc(DL);
+
+ InstInfo.erase(PredTerm);
+ PredTerm->eraseFromParent();
}
//===----------------------------------------------------------------------===//
//
//===----------------------------------------------------------------------===//
PreservedAnalyses ADCEPass::run(Function &F, FunctionAnalysisManager &FAM) {
+ auto &DT = FAM.getResult<DominatorTreeAnalysis>(F);
auto &PDT = FAM.getResult<PostDominatorTreeAnalysis>(F);
- if (!AggressiveDeadCodeElimination(F, PDT).performDeadCodeElimination())
+ if (!AggressiveDeadCodeElimination(F, DT, PDT).performDeadCodeElimination())
return PreservedAnalyses::all();
PreservedAnalyses PA;
PA.preserveSet<CFGAnalyses>();
PA.preserve<GlobalsAA>();
+ PA.preserve<DominatorTreeAnalysis>();
+ PA.preserve<PostDominatorTreeAnalysis>();
return PA;
}
bool runOnFunction(Function &F) override {
if (skipFunction(F))
return false;
+
+ auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
auto &PDT = getAnalysis<PostDominatorTreeWrapperPass>().getPostDomTree();
- return AggressiveDeadCodeElimination(F, PDT).performDeadCodeElimination();
+ return AggressiveDeadCodeElimination(F, DT, PDT)
+ .performDeadCodeElimination();
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
+ // We require DominatorTree here only to update and thus preserve it.
+ AU.addRequired<DominatorTreeWrapperPass>();
AU.addRequired<PostDominatorTreeWrapperPass>();
if (!RemoveControlFlowFlag)
AU.setPreservesCFG();
+ else {
+ AU.addPreserved<DominatorTreeWrapperPass>();
+ AU.addPreserved<PostDominatorTreeWrapperPass>();
+ }
AU.addPreserved<GlobalsAAWrapperPass>();
}
};
char ADCELegacyPass::ID = 0;
INITIALIZE_PASS_BEGIN(ADCELegacyPass, "adce",
"Aggressive Dead Code Elimination", false, false)
+INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
INITIALIZE_PASS_DEPENDENCY(PostDominatorTreeWrapperPass)
INITIALIZE_PASS_END(ADCELegacyPass, "adce", "Aggressive Dead Code Elimination",
false, false)
--- /dev/null
+; RUN: opt < %s -gvn -simplifycfg -adce | llvm-dis
+; RUN: opt < %s -gvn -simplifycfg -adce -verify-dom-info | llvm-dis
+
+; This test makes sure that the DominatorTree properly handles
+; deletion of edges that go to forward-unreachable regions.
+; In this case, %land.end is already forward unreachable when
+; the DT gets informed about the deletion of %entry -> %land.end.
+
+@a = common global i32 0, align 4
+
+define i32 @main() {
+entry:
+ %retval = alloca i32, align 4
+ store i32 0, i32* %retval, align 4
+ %0 = load i32, i32* @a, align 4
+ %cmp = icmp ne i32 %0, 1
+ br i1 %cmp, label %land.rhs, label %land.end4
+
+land.rhs: ; preds = %entry
+ %1 = load i32, i32* @a, align 4
+ %tobool = icmp ne i32 %1, 0
+ br i1 %tobool, label %land.rhs1, label %land.end
+
+land.rhs1: ; preds = %land.rhs
+ br label %land.end
+
+land.end: ; preds = %land.rhs1, %land.rhs
+ %2 = phi i1 [ false, %land.rhs ], [ true, %land.rhs1 ]
+ %land.ext = zext i1 %2 to i32
+ %conv = trunc i32 %land.ext to i16
+ %conv2 = sext i16 %conv to i32
+ %tobool3 = icmp ne i32 %conv2, 0
+ br label %land.end4
+
+land.end4: ; preds = %land.end, %entry
+ %3 = phi i1 [ false, %entry ], [ %tobool3, %land.end ]
+ %land.ext5 = zext i1 %3 to i32
+ ret i32 0
+}