[clang] [lldb] [llvm] [APInt] Fix APInt constructions where value does not fit bitwidth (NFCI) (PR #80309)

[Simon Pilgrim via cfe-commits]

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@@ -28729,7 +28731,7 @@ static SDValue GenerateFixedLengthSVETBL(SDValue Op, SDValue Op1, SDValue Op2,
   unsigned BitsPerElt = VTOp1.getVectorElementType().getSizeInBits();
   unsigned IndexLen = MinSVESize / BitsPerElt;
   unsigned ElementsPerVectorReg = VTOp1.getVectorNumElements();
-  uint64_t MaxOffset = APInt(BitsPerElt, -1, false).getZExtValue();
+  uint64_t MaxOffset = APInt(BitsPerElt, -1, true).getZExtValue();
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RKSimon wrote:

Seems convoluted - `APInt::getAllOnes(BitsPerElt).getZExtValue()` or just do a `~0ULL >> (64 - BitsPerElt)`?

https://github.com/llvm/llvm-project/pull/80309