[ValueTracking] Fix bit width handling in computeKnownBits() for GEPs (#125532)

For GEPs, we have three bit widths involved: The pointer bit width, the
index bit width, and the bit width of the GEP operands.

The correct behavior here is:
* We need to sextOrTrunc the GEP operand to the index width *before*
multiplying by the scale.
* If the index width and pointer width differ, GEP only ever modifies
the low bits. Adds should not overflow into the high bits.

I'm testing this via unit tests because it's a bit tricky to test in IR
with InstCombine canonicalization getting in the way.

0 files changed, 0 insertions, 0 deletions