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add an early out to ProcessBranchOnXOR to speed it up,
handle the case when we can infer an input to the xor from all inputs that agree, instead of going into an infinite loop. Another part of PR6199 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@94321 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -1123,6 +1123,11 @@ bool JumpThreading::ProcessBranchOnXOR(BinaryOperator *BO) {
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isa<ConstantInt>(BO->getOperand(1)))
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isa<ConstantInt>(BO->getOperand(1)))
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return false;
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return false;
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// If the first instruction in BB isn't a phi, we won't be able to infer
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// anything special about any particular predecessor.
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if (!isa<PHINode>(BB->front()))
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return false;
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// If we have a xor as the branch input to this block, and we know that the
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// If we have a xor as the branch input to this block, and we know that the
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// LHS or RHS of the xor in any predecessor is true/false, then we can clone
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// LHS or RHS of the xor in any predecessor is true/false, then we can clone
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// the condition into the predecessor and fix that value to true, saving some
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// the condition into the predecessor and fix that value to true, saving some
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@ -1180,6 +1185,26 @@ bool JumpThreading::ProcessBranchOnXOR(BinaryOperator *BO) {
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BlocksToFoldInto.push_back(XorOpValues[i].second);
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BlocksToFoldInto.push_back(XorOpValues[i].second);
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}
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}
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// If we inferred a value for all of the predecessors, then duplication won't
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// help us. However, we can just replace the LHS or RHS with the constant.
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if (BlocksToFoldInto.size() ==
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cast<PHINode>(BB->front()).getNumIncomingValues()) {
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if (SplitVal == 0) {
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// If all preds provide undef, just nuke the xor, because it is undef too.
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BO->replaceAllUsesWith(UndefValue::get(BO->getType()));
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BO->eraseFromParent();
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} else if (SplitVal->isZero()) {
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// If all preds provide 0, replace the xor with the other input.
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BO->replaceAllUsesWith(BO->getOperand(isLHS));
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BO->eraseFromParent();
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} else {
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// If all preds provide 1, set the computed value to 1.
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BO->setOperand(!isLHS, SplitVal);
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}
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return true;
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}
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// Try to duplicate BB into PredBB.
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// Try to duplicate BB into PredBB.
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return DuplicateCondBranchOnPHIIntoPred(BB, BlocksToFoldInto);
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return DuplicateCondBranchOnPHIIntoPred(BB, BlocksToFoldInto);
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}
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}
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@ -259,3 +259,30 @@ for.cond: ; preds = %for.body, %lor.end
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for.body: ; preds = %for.cond
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for.body: ; preds = %for.cond
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br label %for.cond
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br label %for.cond
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}
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}
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; PR6119
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define i32 @test9(i32 %action) nounwind {
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entry:
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switch i32 %action, label %lor.rhs [
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i32 1, label %if.then
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i32 0, label %lor.end
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]
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if.then: ; preds = %for.cond, %lor.end, %entry
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ret i32 undef
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lor.rhs: ; preds = %entry
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br label %lor.end
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lor.end: ; preds = %lor.rhs, %entry
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%0 = phi i1 [ undef, %lor.rhs ], [ true, %entry ] ; <i1> [#uses=1]
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%cmp103 = xor i1 undef, %0 ; <i1> [#uses=1]
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br i1 %cmp103, label %for.cond, label %if.then
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for.cond: ; preds = %for.body, %lor.end
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br i1 undef, label %if.then, label %for.body
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for.body: ; preds = %for.cond
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br label %for.cond
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}
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