[PATCH] D13040: [SimplifyCFG] Constant fold a branch implied by it's incoming edge

[Philip Reames via llvm-commits]

reames created this revision.
reames added reviewers: hfinkel, sanjoy, majnemer, zhousheng00, spatel.
reames added a subscriber: llvm-commits.

The most common use case is when eliminating redundant range checks in an example like the following:
c = a[i+1] + a[i];

For the moment, the implies function only handles a single simple case.  I plan to extend this function to handle more complex examples, but I wanted to separate a single transform based on it to make review easy.  I'll also be implementing a profile guided version targeted at removing range checks in (a[i] + a[i+1]) as well.  That will follow in a later patch.

In terms of code placement/testing, do folks think it would make sense to implement the implies function in InstructionSimplify?  You can phrase an implication question as icmpa <= icmpb.  Having it in InstSimpify would make it easier to test, but I'm not sure we actually want to start handling complex implications in InstSimplify.  Thoughts?


http://reviews.llvm.org/D13040

Files:
  lib/Transforms/Utils/SimplifyCFG.cpp
  test/Transforms/SimplifyCFG/implied-cond.ll

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