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[IndVarSimplify] Widen loop compare instructions.

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This improves other optimizations such as LSR.  A sext may be added to the
compare's other operand, but this can often be hoisted outside of the loop.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@217953 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chad Rosier
2014-09-17 14:10:33 +00:00
parent a34cab9be7
commit c5f6b53403
4 changed files with 208 additions and 8 deletions
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lib/Transforms/Scalar/IndVarSimplify.cpp
+36 -3
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@@ -762,6 +762,8 @@ protected:
Instruction *WidenIVUse(NarrowIVDefUse DU, SCEVExpander &Rewriter);
bool WidenLoopCompare(NarrowIVDefUse DU);
void pushNarrowIVUsers(Instruction *NarrowDef, Instruction *WideDef);
};
} // anonymous namespace
@@ -926,6 +928,32 @@ static void truncateIVUse(NarrowIVDefUse DU, DominatorTree *DT) {
DU.NarrowUse->replaceUsesOfWith(DU.NarrowDef, Trunc);
}
/// If the narrow use is a compare instruction, then widen the compare
// (and possibly the other operand). The extend operation is hoisted into the
// loop preheader as far as possible.
bool WidenIV::WidenLoopCompare(NarrowIVDefUse DU) {
ICmpInst *Cmp = dyn_cast<ICmpInst>(DU.NarrowUse);
if (!Cmp)
return false;
Value *Op = Cmp->getOperand(Cmp->getOperand(0) == DU.NarrowDef ? 1 : 0);
unsigned CastWidth = SE->getTypeSizeInBits(Op->getType());
unsigned IVWidth = SE->getTypeSizeInBits(WideType);
assert (CastWidth <= IVWidth && "Unexpected width while widening compare.");
// Widen the compare instruction.
IRBuilder<> Builder(getInsertPointForUses(DU.NarrowUse, DU.NarrowDef, DT));
DU.NarrowUse->replaceUsesOfWith(DU.NarrowDef, DU.WideDef);
// Widen the other operand of the compare, if necessary.
if (CastWidth < IVWidth) {
bool IsSigned = CmpInst::isSigned(Cmp->getPredicate());
Value *ExtOp = getExtend(Op, WideType, IsSigned, Cmp);
DU.NarrowUse->replaceUsesOfWith(Op, ExtOp);
}
return true;
}
/// WidenIVUse - Determine whether an individual user of the narrow IV can be
/// widened. If so, return the wide clone of the user.
Instruction *WidenIV::WidenIVUse(NarrowIVDefUse DU, SCEVExpander &Rewriter) {
@@ -993,10 +1021,15 @@ Instruction *WidenIV::WidenIVUse(NarrowIVDefUse DU, SCEVExpander &Rewriter) {
// Does this user itself evaluate to a recurrence after widening?
const SCEVAddRecExpr *WideAddRec = GetWideRecurrence(DU.NarrowUse);
if (!WideAddRec)
WideAddRec = GetExtendedOperandRecurrence(DU);
if (!WideAddRec) {
WideAddRec = GetExtendedOperandRecurrence(DU);
}
if (!WideAddRec) {
// If use is a loop condition, try to promote the condition instead of
// truncating the IV first.
if (WidenLoopCompare(DU))
return nullptr;
// This user does not evaluate to a recurence after widening, so don't
// follow it. Instead insert a Trunc to kill off the original use,
// eventually isolating the original narrow IV so it can be removed.