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indvars: generalize SCEV getPreStartForSignExtend.

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Handle general Add expressions to avoid leaving around redundant
32-bit IVs.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@140701 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Andrew Trick 2011-09-28 17:02:54 +00:00
parent ed0e4c85c4
commit f63ae2159d
1 changed files with 14 additions and 2 deletions
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16
lib/Analysis/ScalarEvolution.cpp
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@ -1070,14 +1070,26 @@ static const SCEV *getPreStartForSignExtend(const SCEVAddRecExpr *AR,
// Check for a simple looking step prior to loop entry.
const SCEVAddExpr *SA = dyn_cast<SCEVAddExpr>(Start);
if (!SA || SA->getNumOperands() != 2 || SA->getOperand(0) != Step)
if (!SA)
return 0;
// Create an AddExpr for "PreStart" after subtracting Step. Full SCEV
// subtraction is expensive. For this purpose, perform a quick and dirty
// difference, by checking for Step in the operand list.
SmallVector<const SCEV *, 4> DiffOps;
for (SCEVAddExpr::op_iterator I = SA->op_begin(), E = SA->op_end();
I != E; ++I) {
if (*I != Step)
DiffOps.push_back(*I);
}
if (DiffOps.size() == SA->getNumOperands())
return 0;
// This is a postinc AR. Check for overflow on the preinc recurrence using the
// same three conditions that getSignExtendedExpr checks.
// 1. NSW flags on the step increment.
const SCEV *PreStart = SA->getOperand(1);
const SCEV *PreStart = SE->getAddExpr(DiffOps, SA->getNoWrapFlags());
const SCEVAddRecExpr *PreAR = dyn_cast<SCEVAddRecExpr>(
SE->getAddRecExpr(PreStart, Step, L, SCEV::FlagAnyWrap));