[PATCH] D19550: [InstCombine] Determine the result of a select based on a dominating condition.

[Chad Rosier via llvm-commits]

mcrosier created this revision.
mcrosier added reviewers: Gerolf, majnemer, sanjoy.
mcrosier added subscribers: llvm-commits, gberry, bmakam, Gerolf.

This patch attempts to determine the result of a select based on a dominating condition.  This is similar to what is done in JumpThreading and SimplifyCFG, except those passes on consider conditional branches and not selects.

AFAICT, the transformation in pr21210.ll is safe, but the comments in the lit test seem to indicate otherwise.  

@Gerolf - Would you mind helping me better understand what pr21210.ll is trying to test?

I didn't run into any correctness issues with the llvm-test suite or SPEC200X.

Please take a look,
Chad

http://reviews.llvm.org/D19550

Files:
  lib/Analysis/ValueTracking.cpp
  lib/Transforms/InstCombine/InstCombineSelect.cpp
  test/Transforms/InstCombine/pr21210.ll
  test/Transforms/InstCombine/select-implied.ll

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