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-rw-r--r--llvm/lib/Analysis/ValueTracking.cpp14
1 files changed, 12 insertions, 2 deletions
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 5caffee8fe7..d2a1f8737cd 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -1375,8 +1375,18 @@ static void computeKnownBitsFromOperator(Operator *I, APInt &KnownZero,
break;
}
case Intrinsic::ctpop: {
- unsigned LowBits = Log2_32(BitWidth)+1;
- KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - LowBits);
+ computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, DL,
+ Depth + 1, Q);
+ // We can bound the space the count needs. Also, bits known to be zero
+ // can't contribute to the population.
+ unsigned BitsPossiblySet = BitWidth - KnownZero2.countPopulation();
+ unsigned LeadingZeros =
+ APInt(BitWidth, BitsPossiblySet).countLeadingZeros();
+ assert(LeadingZeros >= 0 && LeadingZeros <= BitWidth);
+ KnownZero |= APInt::getHighBitsSet(BitWidth, LeadingZeros);
+ KnownOne &= ~KnownZero;
+ // TODO: we could bound KnownOne using the lower bound on the number
+ // of bits which might be set provided by popcnt KnownOne2.
break;
}
case Intrinsic::fabs: {
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