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Add a missed SCEV fold that is required to continue analyzing the IR produced

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by indvars through the scev expander.

trunc(add x, y) --> add(trunc x, y). Currently SCEV largely folds the other way
which is probably wrong, but preserved to minimize churn. Instcombine doesn't
do this fold either, demonstrating a missed optz'n opportunity on code doing
add+trunc+add.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@123838 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Nick Lewycky
2011-01-19 16:59:46 +00:00
parent 3abd75bf1d
commit 30aa8b13c9
2 changed files with 23 additions and 1 deletions
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14
lib/Analysis/ScalarEvolution.cpp
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@@ -819,6 +819,20 @@ const SCEV *ScalarEvolution::getTruncateExpr(const SCEV *Op,
if (const SCEVZeroExtendExpr *SZ = dyn_cast<SCEVZeroExtendExpr>(Op))
return getTruncateOrZeroExtend(SZ->getOperand(), Ty);
// trunc(x1+x2+...+xN) --> trunc(x1)+trunc(x2)+...+trunc(xN) if we can
// eliminate all the truncates.
if (const SCEVAddExpr *SA = dyn_cast<SCEVAddExpr>(Op)) {
SmallVector<const SCEV *, 4> Operands;
bool hasTrunc = false;
for (unsigned i = 0, e = SA->getNumOperands(); i != e && !hasTrunc; ++i) {
const SCEV *S = getTruncateExpr(SA->getOperand(i), Ty);
hasTrunc = isa<SCEVTruncateExpr>(S);
Operands.push_back(S);
}
if (!hasTrunc)
return getAddExpr(Operands, false, false);
}
// If the input value is a chrec scev, truncate the chrec's operands.
if (const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(Op)) {
SmallVector<const SCEV *, 4> Operands;