[PATCH] D105674: [GlobalISel] Use GCDTy when extracting GCD ty from leftover regs in insertParts

[Jessica Paquette via Phabricator via llvm-commits]

paquette created this revision.
paquette added reviewers: arsenm, aemerson.
Herald added subscribers: hiraditya, rovka.
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`LegalizerHelper::insertParts` uses `extractGCDType` on registers split into a desired type and a smaller leftover type. This is used to populate a list of registers. Each register in the list will have the same type as returned by `extractGCDType`.

If we have

- `ResultTy` = s792
- `PartTy` = s64
- `LeftoverTy` = s24

When we call `extractGCDType`, we'll end up with two different types appended to the list:

Part: gcd(792, 64, 24) => s8
Leftover: gcd(792, 24, 24) => s24

When this happens, we'll hit an assert while trying to build a G_MERGE_VALUES.

This patch changes the code for the leftover type so that we reuse the GCD from the desired type.

e.g.

Leftover: gcd(792, 8, 24) => s8

It also adds an assert that the types we get from both calls to `extractGCDType` are actually the same.

https://llvm.godbolt.org/z/137Kqxj6j


https://reviews.llvm.org/D105674

Files:
  llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
  llvm/test/CodeGen/AArch64/GlobalISel/legalize-constant.mir

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