forked from OSchip/llvm-project
[SimplifyCFG] Prefer a simplification based on a dominating condition.
Rather than merge two branches with a common destination. Differential Revision: http://reviews.llvm.org/D19743 llvm-svn: 268735
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Chad Rosier
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c7e4239fab
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4ab37c0037
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@ -2706,26 +2706,6 @@ static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI,
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if (CE->canTrap())
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if (CE->canTrap())
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return false;
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return false;
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// If BI is reached from the true path of PBI and PBI's condition implies
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// BI's condition, we know the direction of the BI branch.
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if ((PBI->getSuccessor(0) == BI->getParent() ||
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PBI->getSuccessor(1) == BI->getParent()) &&
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PBI->getSuccessor(0) != PBI->getSuccessor(1) &&
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BB->getSinglePredecessor()) {
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bool FalseDest = PBI->getSuccessor(1) == BI->getParent();
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Optional<bool> Implication = isImpliedCondition(
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PBI->getCondition(), BI->getCondition(), DL, FalseDest);
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if (Implication) {
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// Turn this into a branch on constant.
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auto *OldCond = BI->getCondition();
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ConstantInt *CI = *Implication ? ConstantInt::getTrue(BB->getContext())
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: ConstantInt::getFalse(BB->getContext());
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BI->setCondition(CI);
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RecursivelyDeleteTriviallyDeadInstructions(OldCond);
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return true; // Nuke the branch on constant.
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}
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}
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// If both branches are conditional and both contain stores to the same
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// If both branches are conditional and both contain stores to the same
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// address, remove the stores from the conditionals and create a conditional
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// address, remove the stores from the conditionals and create a conditional
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// merged store at the end.
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// merged store at the end.
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@ -5149,6 +5129,30 @@ bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder) {
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if (SimplifyBranchOnICmpChain(BI, Builder, DL))
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if (SimplifyBranchOnICmpChain(BI, Builder, DL))
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return true;
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return true;
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// If this basic block has a single dominating predecessor block and the
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// dominating block's condition implies BI's condition, we know the direction
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// of the BI branch.
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if (BasicBlock *Dom = BB->getSinglePredecessor()) {
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auto *PBI = dyn_cast_or_null<BranchInst>(Dom->getTerminator());
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if (PBI && PBI->isConditional() &&
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PBI->getSuccessor(0) != PBI->getSuccessor(1) &&
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(PBI->getSuccessor(0) == BB || PBI->getSuccessor(1) == BB)) {
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bool CondIsFalse = PBI->getSuccessor(1) == BB;
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Optional<bool> Implication = isImpliedCondition(
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PBI->getCondition(), BI->getCondition(), DL, CondIsFalse);
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if (Implication) {
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// Turn this into a branch on constant.
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auto *OldCond = BI->getCondition();
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ConstantInt *CI = *Implication
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? ConstantInt::getTrue(BB->getContext())
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: ConstantInt::getFalse(BB->getContext());
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BI->setCondition(CI);
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RecursivelyDeleteTriviallyDeadInstructions(OldCond);
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return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
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}
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}
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}
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// If this basic block is ONLY a compare and a branch, and if a predecessor
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// If this basic block is ONLY a compare and a branch, and if a predecessor
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// branches to us and one of our successors, fold the comparison into the
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// branches to us and one of our successors, fold the comparison into the
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// predecessor and use logical operations to pick the right destination.
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// predecessor and use logical operations to pick the right destination.
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@ -25,6 +25,54 @@ define void @test3(i1 %T) {
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; CHECK-NEXT: ret void
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; CHECK-NEXT: ret void
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}
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}
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; Folding branch to a common destination.
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; CHECK-LABEL: @test4_fold
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; CHECK: %cmp1 = icmp eq i32 %a, %b
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; CHECK: %cmp2 = icmp ugt i32 %a, 0
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; CHECK: %or.cond = and i1 %cmp1, %cmp2
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; CHECK: br i1 %or.cond, label %else, label %untaken
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; CHECK-NOT: taken:
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; CHECK: ret void
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define void @test4_fold(i32 %a, i32 %b) {
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%cmp1 = icmp eq i32 %a, %b
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br i1 %cmp1, label %taken, label %untaken
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taken:
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%cmp2 = icmp ugt i32 %a, 0
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br i1 %cmp2, label %else, label %untaken
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else:
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call void @foo()
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ret void
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untaken:
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ret void
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}
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; Prefer a simplification based on a dominating condition rather than folding a
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; branch to a common destination.
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; CHECK-LABEL: @test4
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; CHECK-NOT: br
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; CHECK-NOT: br
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; CHECK-NOT: call
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; CHECK: ret void
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define void @test4_no_fold(i32 %a, i32 %b) {
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%cmp1 = icmp eq i32 %a, %b
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br i1 %cmp1, label %taken, label %untaken
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taken:
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%cmp2 = icmp ugt i32 %a, %b
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br i1 %cmp2, label %else, label %untaken
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else:
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call void @foo()
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ret void
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untaken:
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ret void
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}
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declare void @foo()
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; PR5795
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; PR5795
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define void @test5(i32 %A) {
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define void @test5(i32 %A) {
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