Split off from D150398 to avoid builder-related diff changes there.
Using IRBuilder to create ICmps simplifies the result if both operands
are constants.
Reviewed By: Ayal
Differential Revision: https://reviews.llvm.org/D158332
Update computeMinimumValueSizes to check if an instruction's operands
can safely be truncated.
If more than MinBW bits are demanded by for the operand or if the
operand is a constant and cannot be safely truncated, it is not safe to
evaluate the instruction in the narrower MinBW. Skip those cases.
Fixes https://github.com/llvm/llvm-project/issues/47927
Reviewed By: nikic
Differential Revision: https://reviews.llvm.org/D154717
