[PATCH] D79116: [InstCombine] fold fpext into Xitofp

[Sanjay Patel via Phabricator via llvm-commits]

spatel created this revision.
spatel added reviewers: pcordes, RKSimon, scanon, zhengyangl, aqjune, nlopes, regehr.
Herald added subscribers: hiraditya, mcrosier.
Herald added a project: LLVM.

We can combine a floating-point extension cast with a conversion from integer if we know the earlier cast is exact. For example:
fpext (sitofp (fptosi half F to iN) to float) to double --> sitofp (fptosi half F to iN) to double

This is an optimization suggested in PR36617:
https://bugs.llvm.org/show_bug.cgi?id=36617#c19

I left the mismatched unsigned -> signed pattern out of this patch just in case there's some weird type combo that I'm not seeing. I can add that here if there's no concern.

This gives us another opportunity to test-drive Alive2 with FP ops:
http://volta.cs.utah.edu:8080/z/NfYne7


https://reviews.llvm.org/D79116

Files:
  llvm/include/llvm/IR/PatternMatch.h
  llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
  llvm/test/Transforms/InstCombine/fpextend.ll

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