[PATCH] D18777: [ValueTracking] An improvement to IR ValueTracking on Non-negative Integers

[Li Huang via llvm-commits]

lihuang created this revision.
lihuang added reviewers: mbodart, reames, sanjoy.
lihuang added a subscriber: llvm-commits.

An improvement to IR ValueTracking on Non-negative Integers.

Current IR ValueTracking does not recognize the cases below, thus hiding optimization opportunities.

     1. Induction variable starting from a non-negative integer and incrementing in each iteration is known to be non-negative.
     2. Result of left shifting a non-negative integer with nsw flag is known to be non-negative.

This change is a small improvement to computeKnownBits on PHI node and Shift. 

Patch by Ruben Perez.  

http://reviews.llvm.org/D18777

Files:
  lib/Analysis/ValueTracking.cpp
  lib/Transforms/Scalar/IndVarSimplify.cpp
  test/Analysis/ValueTracking/shift-nsw.ll
  test/Transforms/BBVectorize/loop1.ll

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