[llvm] [GlobalISel] Check width of APInts in Reassoc PtrAdd combine (PR #84335)

[Jay Foad via llvm-commits]

jayfoad wrote:

> If you ask for getIConstantVRegValWithLookThrough from a s64 register, there is no guarantee that the bitwidth of APInt is 64 bit.

Yes that should be guaranteed. If `getIConstantVRegValWithLookThrough` looks through a truncation or extension, it truncates or extends the APInt accordingly before returning it. Do you have an example where this does not work?

https://github.com/llvm/llvm-project/pull/84335