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Do not try to optimize PHI nodes with incredibly high degree. This reduces SCCP

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time from 615s to 1.49s on a large testcase that has a gigantic switch statement
that all of the blocks in the function go to (an intepreter).

llvm-svn: 12442
This commit is contained in:
Chris Lattner 2004-03-16 19:49:59 +00:00
parent 2175b35b46
commit dc22f37eb5
1 changed files with 7 additions and 0 deletions
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7
lib/Transforms/Scalar/SCCP.cpp
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@ -500,6 +500,13 @@ void SCCP::visitPHINode(PHINode &PN) {
return; // Quick exit
}
// Super-extra-high-degree PHI nodes are unlikely to ever be marked constant,
// and slow us down a lot. Just mark them overdefined.
if (PN.getNumIncomingValues() > 64) {
markOverdefined(PNIV, &PN);
return;
}
// Look at all of the executable operands of the PHI node. If any of them
// are overdefined, the PHI becomes overdefined as well. If they are all
// constant, and they agree with each other, the PHI becomes the identical