[PATCH] D97064: [SCEV] Infer known bits from known sign bits
Philip Reames via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Tue Mar 9 12:37:39 PST 2021
This revision was landed with ongoing or failed builds.
This revision was automatically updated to reflect the committed changes.
Closed by commit rGa25b537bf437: [SCEV] Infer known bits from known sign bits (authored by reames).
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D97064/new/
https://reviews.llvm.org/D97064
Files:
llvm/lib/Analysis/ScalarEvolution.cpp
Index: llvm/lib/Analysis/ScalarEvolution.cpp
===================================================================
--- llvm/lib/Analysis/ScalarEvolution.cpp
+++ llvm/lib/Analysis/ScalarEvolution.cpp
@@ -5848,24 +5848,31 @@
KnownBits Known = computeKnownBits(U->getValue(), DL, 0, &AC, nullptr, &DT);
if (Known.getBitWidth() != BitWidth)
Known = Known.zextOrTrunc(BitWidth);
- // If Known does not result in full-set, intersect with it.
- if (Known.getMinValue() != Known.getMaxValue() + 1)
- ConservativeResult = ConservativeResult.intersectWith(
- ConstantRange(Known.getMinValue(), Known.getMaxValue() + 1),
- RangeType);
// ValueTracking may be able to compute a tighter result for the number of
// sign bits than for the value of those sign bits.
unsigned NS = ComputeNumSignBits(U->getValue(), DL, 0, &AC, nullptr, &DT);
- // If the pointer size is larger than the index size type, this can cause
- // NS to be larger than BitWidth. So compensate for this.
if (U->getType()->isPointerTy()) {
+ // If the pointer size is larger than the index size type, this can cause
+ // NS to be larger than BitWidth. So compensate for this.
unsigned ptrSize = DL.getPointerTypeSizeInBits(U->getType());
int ptrIdxDiff = ptrSize - BitWidth;
if (ptrIdxDiff > 0 && ptrSize > BitWidth && NS > (unsigned)ptrIdxDiff)
NS -= ptrIdxDiff;
}
+ if (NS > 1) {
+ // If we know any of the sign bits, we know all of the sign bits.
+ if (!Known.Zero.getHiBits(NS).isNullValue())
+ Known.Zero.setHighBits(NS);
+ if (!Known.One.getHiBits(NS).isNullValue())
+ Known.One.setHighBits(NS);
+ }
+
+ if (Known.getMinValue() != Known.getMaxValue() + 1)
+ ConservativeResult = ConservativeResult.intersectWith(
+ ConstantRange(Known.getMinValue(), Known.getMaxValue() + 1),
+ RangeType);
if (NS > 1)
ConservativeResult = ConservativeResult.intersectWith(
ConstantRange(APInt::getSignedMinValue(BitWidth).ashr(NS - 1),
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