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add an early out to ProcessBranchOnXOR to speed it up,

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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
This commit is contained in:
Chris Lattner 2010-01-23 19:16:25 +00:00
parent 8231fd1e6c
commit 2dd7657a5b
2 changed files with 52 additions and 0 deletions
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25
lib/Transforms/Scalar/JumpThreading.cpp
View File

@ -1123,6 +1123,11 @@ bool JumpThreading::ProcessBranchOnXOR(BinaryOperator *BO) {
isa<ConstantInt>(BO->getOperand(1))) isa<ConstantInt>(BO->getOperand(1)))
return false; return false;
// If the first instruction in BB isn't a phi, we won't be able to infer
// anything special about any particular predecessor.
if (!isa<PHINode>(BB->front()))
return false;
// If we have a xor as the branch input to this block, and we know that the // If we have a xor as the branch input to this block, and we know that the
// LHS or RHS of the xor in any predecessor is true/false, then we can clone // LHS or RHS of the xor in any predecessor is true/false, then we can clone
// the condition into the predecessor and fix that value to true, saving some // the condition into the predecessor and fix that value to true, saving some
@ -1180,6 +1185,26 @@ bool JumpThreading::ProcessBranchOnXOR(BinaryOperator *BO) {
BlocksToFoldInto.push_back(XorOpValues[i].second); BlocksToFoldInto.push_back(XorOpValues[i].second);
} }
// If we inferred a value for all of the predecessors, then duplication won't
// help us. However, we can just replace the LHS or RHS with the constant.
if (BlocksToFoldInto.size() ==
cast<PHINode>(BB->front()).getNumIncomingValues()) {
if (SplitVal == 0) {
// If all preds provide undef, just nuke the xor, because it is undef too.
BO->replaceAllUsesWith(UndefValue::get(BO->getType()));
BO->eraseFromParent();
} else if (SplitVal->isZero()) {
// If all preds provide 0, replace the xor with the other input.
BO->replaceAllUsesWith(BO->getOperand(isLHS));
BO->eraseFromParent();
} else {
// If all preds provide 1, set the computed value to 1.
BO->setOperand(!isLHS, SplitVal);
}
return true;
}
// Try to duplicate BB into PredBB. // Try to duplicate BB into PredBB.
return DuplicateCondBranchOnPHIIntoPred(BB, BlocksToFoldInto); return DuplicateCondBranchOnPHIIntoPred(BB, BlocksToFoldInto);
} }

27
test/Transforms/JumpThreading/crash.ll
View File

@ -259,3 +259,30 @@ for.cond: ; preds = %for.body, %lor.end
for.body: ; preds = %for.cond for.body: ; preds = %for.cond
br label %for.cond br label %for.cond
} }
; PR6119
define i32 @test9(i32 %action) nounwind {
entry:
switch i32 %action, label %lor.rhs [
i32 1, label %if.then
i32 0, label %lor.end
]
if.then: ; preds = %for.cond, %lor.end, %entry
ret i32 undef
lor.rhs: ; preds = %entry
br label %lor.end
lor.end: ; preds = %lor.rhs, %entry
%0 = phi i1 [ undef, %lor.rhs ], [ true, %entry ] ; <i1> [#uses=1]
%cmp103 = xor i1 undef, %0 ; <i1> [#uses=1]
br i1 %cmp103, label %for.cond, label %if.then
for.cond: ; preds = %for.body, %lor.end
br i1 undef, label %if.then, label %for.body
for.body: ; preds = %for.cond
br label %for.cond
}