[PATCH] D125511: [InstCombine] Merging constant-indexed GEP of GEP in both directions

[William Junda Huang via Phabricator via llvm-commits]

huangjd added a comment.

@nikic 
I will add converting constant GEP to i8* in the next patch. The existing merging functionality can handle GEP with not all constant indices, such as

  %1 = gep {i32, i32, i32}, ptr %p, i64 %a, i32 1
  %2 = gep i32, ptr %1, i64 1

Such expression cannot be convert to GEP of i8 without creating a complicated index expression, which is basically moving instruction selection to the front. It is unreasonable that merge only allows one direction but not the other, given use-def constraints satisfied.


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D125511/new/

https://reviews.llvm.org/D125511