[llvm] [DemandedBits] Support non-constant shift amounts (PR #148880)

[Ramkumar Ramachandra via llvm-commits]

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@@ -183,6 +196,17 @@ void DemandedBits::determineLiveOperandBits(
           AB |= APInt::getHighBitsSet(BitWidth, ShiftAmt+1);
         else if (S->hasNoUnsignedWrap())
           AB |= APInt::getHighBitsSet(BitWidth, ShiftAmt);
+      } else {
+        ComputeKnownBits(BitWidth, UserI->getOperand(1), nullptr);
+        unsigned Min = Known.getMinValue().getLimitedValue(BitWidth - 1);
+        unsigned Max = Known.getMaxValue().getLimitedValue(BitWidth - 1);
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artagnon wrote:

getLimitedValue returns uint64_t, and it would be best not to narrow its type unnecessarily?

https://github.com/llvm/llvm-project/pull/148880