[PATCH] D107330: [GlobalISel] Combine shr(shl x, c1), c2 to G_SBFX/G_UBFX

[Dominik Montada via Phabricator via llvm-commits]

gargaroff marked an inline comment as done.
gargaroff added inline comments.


================
Comment at: llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp:4145
+  LLT ExtractTy = getTargetLowering().getPreferredShiftAmountTy(Ty);
+  if (!LI || !LI->isLegalOrCustom({ExtrOpcode, {Ty, ExtractTy}}))
+    return false;
----------------
foad wrote:
> Lots of combines use `isLegalOrBeforeLegalizer`, i.e. they do apply before legalization. Is there a reason you have made this one different, so it does not apply before legalization?
For that I followed the other bitfield extract combine. I'm guessing because there is only `widenScalar` implemented for `G_SBFX` and `G_UBFX`, so you wouldn't even be able to lower it if it would be illegal for your target.

Once at least the `lower` action is implemented, this check can be changed to make this combine also run before the legalizer.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D107330/new/

https://reviews.llvm.org/D107330