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GVN: Fix quadratic runtime on the number of switch cases.

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No intended behavior change.  This was introduced in r162023.  With the fixed
algorithm a Release build of ARMInstPrinter.cpp goes from 16s to 10s on a
2011 MBP.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@162559 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Benjamin Kramer 2012-08-24 15:06:28 +00:00
parent 4d320db5d1
commit bd7684c94c
1 changed files with 10 additions and 2 deletions
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12
lib/Transforms/Scalar/GVN.cpp
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@ -2231,12 +2231,20 @@ bool GVN::processInstruction(Instruction *I) {
Value *SwitchCond = SI->getCondition();
BasicBlock *Parent = SI->getParent();
bool Changed = false;
// Remember how many outgoing edges there are to every successor.
SmallDenseMap<BasicBlock *, unsigned, 16> SwitchEdges;
for (unsigned i = 0, n = SI->getNumSuccessors(); i != n; ++i)
++SwitchEdges[SI->getSuccessor(i)];
for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
i != e; ++i) {
BasicBlock *Dst = i.getCaseSuccessor();
BasicBlockEdge E(Parent, Dst);
if (E.isSingleEdge())
// If there is only a single edge, propagate the case value into it.
if (SwitchEdges.lookup(Dst) == 1) {
BasicBlockEdge E(Parent, Dst);
Changed |= propagateEquality(SwitchCond, i.getCaseValue(), E);
}
}
return Changed;
}