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Optimize conditional branch on i1 phis with non-constant inputs.
This turns: eq: %3 = icmp eq i32 %1, %2 br label %join ne: %4 = icmp ne i32 %1, %2 br label %join join: %5 = phi i1 [%3, %eq], [%4, %ne] br i1 %5, label %yes, label %no => eq: %3 = icmp eq i32 %1, %2 br i1 %3, label %yes, label %no ne: %4 = icmp ne i32 %1, %2 br i1 %4, label %yes, label %no git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@69102 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -51,6 +51,7 @@ namespace {
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void SimplifyPredecessors(BranchInst *BI);
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void SimplifyPredecessors(SwitchInst *SI);
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void RevectorBlockTo(BasicBlock *FromBB, BasicBlock *ToBB);
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bool RevectorBlockTo(BasicBlock *FromBB, Value *Cond, BranchInst *BI);
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};
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}
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@ -160,12 +161,11 @@ void CondProp::SimplifyPredecessors(BranchInst *BI) {
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// Ok, we have this really simple case, walk the PHI operands, looking for
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// constants. Walk from the end to remove operands from the end when
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// possible, and to avoid invalidating "i".
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for (unsigned i = PN->getNumIncomingValues(); i != 0; --i)
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if (ConstantInt *CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i-1))) {
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// If we have a constant, forward the edge from its current to its
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// ultimate destination.
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RevectorBlockTo(PN->getIncomingBlock(i-1),
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BI->getSuccessor(CB->isZero()));
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for (unsigned i = PN->getNumIncomingValues(); i != 0; --i) {
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Value *InVal = PN->getIncomingValue(i-1);
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if (!RevectorBlockTo(PN->getIncomingBlock(i-1), InVal, BI))
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continue;
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++NumBrThread;
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// If there were two predecessors before this simplification, or if the
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@ -242,3 +242,44 @@ void CondProp::RevectorBlockTo(BasicBlock *FromBB, BasicBlock *ToBB) {
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MadeChange = true;
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}
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bool CondProp::RevectorBlockTo(BasicBlock *FromBB, Value *Cond, BranchInst *BI){
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BranchInst *FromBr = cast<BranchInst>(FromBB->getTerminator());
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if (!FromBr->isUnconditional())
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return false;
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// Get the old block we are threading through.
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BasicBlock *OldSucc = FromBr->getSuccessor(0);
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// If the condition is a constant, simply revector the unconditional branch at
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// the end of FromBB to one of the successors of its current successor.
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if (ConstantInt *CB = dyn_cast<ConstantInt>(Cond)) {
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BasicBlock *ToBB = BI->getSuccessor(CB->isZero());
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// OldSucc had multiple successors. If ToBB has multiple predecessors, then
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// the edge between them would be critical, which we already took care of.
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// If ToBB has single operand PHI node then take care of it here.
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FoldSingleEntryPHINodes(ToBB);
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// Update PHI nodes in OldSucc to know that FromBB no longer branches to it.
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OldSucc->removePredecessor(FromBB);
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// Change FromBr to branch to the new destination.
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FromBr->setSuccessor(0, ToBB);
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} else {
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// Insert the new conditional branch.
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BranchInst::Create(BI->getSuccessor(0), BI->getSuccessor(1), Cond, FromBr);
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FoldSingleEntryPHINodes(BI->getSuccessor(0));
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FoldSingleEntryPHINodes(BI->getSuccessor(1));
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// Update PHI nodes in OldSucc to know that FromBB no longer branches to it.
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OldSucc->removePredecessor(FromBB);
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// Delete the old branch.
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FromBr->eraseFromParent();
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}
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MadeChange = true;
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return true;
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}
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26
test/Transforms/CondProp/phisimplify3.ll
Normal file
26
test/Transforms/CondProp/phisimplify3.ll
Normal file
@ -0,0 +1,26 @@
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; RUN: llvm-as < %s | opt -condprop | llvm-dis | not grep phi
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define i32 @foo(i1, i32, i32) {
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prologue:
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br i1 %0, label %eq, label %ne
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eq: ; preds = %prologue
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store i32 0, i32* inttoptr (i32 10000 to i32*)
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%3 = icmp eq i32 %1, %2 ; <i1> [#uses=1]
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br label %join
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ne: ; preds = %prologue
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%4 = icmp ne i32 %1, %2 ; <i1> [#uses=1]
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br label %join
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join: ; preds = %ne, %eq
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%5 = phi i1 [ %3, %eq ], [ %4, %ne ] ; <i1> [#uses=1]
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br i1 %5, label %yes, label %no
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yes: ; preds = %join
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store i32 0, i32* inttoptr (i32 20000 to i32*)
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ret i32 5
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no: ; preds = %join
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ret i32 20
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}
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