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we can only thread blocks when there is a pred we can determine the succ of.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@50003 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2008-04-20 21:18:09 +00:00
parent 177480b7ed
commit f9065a904f
1 changed files with 17 additions and 2 deletions

19
lib/Transforms/Scalar/JumpThreading.cpp

@ -134,15 +134,30 @@ bool JumpThreading::ThreadBlock(BasicBlock &BB) {
PHINode *PN = dyn_cast<PHINode>(Condition);
if (!PN || PN->getParent() != &BB) return false;
// See if the phi node has any constant values. If so, we can determine where
// the corresponding predecessor will branch.
unsigned PredNo = ~0U;
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
if (isa<ConstantInt>(PN->getIncomingValue(i))) {
PredNo = i;
break;
}
}
// If no incoming value has a constant, we don't know the destination of any
// predecessors.
if (PredNo == ~0U)
return false;
// See if the cost of duplicating this block is low enough.
unsigned JumpThreadCost = getJumpThreadDuplicationCost(BB);
if (JumpThreadCost > Threshold) {
DOUT << " Not threading BB '" << BB.getNameStart()
<< "': Cost is too high: " << JumpThreadCost << "\n";
<< "' - Cost is too high: " << JumpThreadCost << "\n";
return false;
}
DOUT << " Threading BB '" << BB.getNameStart() << "'. Cost is : "
DOUT << " Threading BB '" << BB.getNameStart() << "'. Cost is: "
<< JumpThreadCost << "\n";
return false;