[Hexagon] Fix UB from left shift of negative in SelectSHL (#181235)
Perform left shifts in unsigned arithmetic in SelectSHL to avoid
undefined behavior when the multiply constant is negative. The result is
cast back to int32_t for the subsequent isInt<9> range check.
Also fix a similar issue where shifting 1 by up to 31 could shift into
the sign bit.
This fixes the UBSan issue in ISelDAGtoDAG:
/local/mnt/workspace/bcain-20260212_105837/llvm-project/llvm/lib/Target/Hexagon/HexagonISelDAGToDAG.cpp:597
:44: runtime error: left shift of negative value -1431655765
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior
/local/mnt/workspace/bcain-20260212_105837/llvm-project/llvm/lib/Target/Hexagon/HexagonISelDAGToDAG.cpp:597:44
in
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