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

[Panagiotis Karouzakis 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);
+        uint64_t Min = Known.getMinValue().getLimitedValue(BitWidth - 1);
+        uint64_t Max = Known.getMaxValue().getLimitedValue(BitWidth - 1);
+        // similar to Lshr case
+        GetShiftedRange(Min, Max, /*ShiftLeft=*/false);
+        const auto *S = cast<ShlOperator>(UserI);
+        if (S->hasNoSignedWrap())
+          AB |= APInt::getHighBitsSet(BitWidth, Max + 1);
+        else if (S->hasNoUnsignedWrap())
+          AB |= APInt::getHighBitsSet(BitWidth, Max);
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karouzakisp wrote:

@dtcxzyw here is the commit hash

6e547c51192976ebf0c1cead3c84deb92253cd5c

It's from my branch at 

[demanded-bit-exp](https://github.com/karouzakisp/llvm-project/tree/demanded-bits-exp)

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