[PATCH] D15397: [EarlyCSE] DSE of stores which write back loaded values

[Philip Reames via llvm-commits]

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

Extend EarlyCSE with an additional style of dead store elimination.  If we write back a value just read from that memory location, we can eliminate the store under the assumption that the value hasn't changed.  

I'd really appreciate someone taking a close look at my "dse5" test case.  I want to make sure the logic involved holds up.  For normal loads and stores it clearly does - for the store to change the value, there must be a race.  I believe it also holds for unordered atomics, but would really like a second opinion.

I'm implementing this mostly because I noticed the omission when looking at the code.  It seemed strange to have InstCombine have a peephole which was more powerful than EarlyCSE.  :)

http://reviews.llvm.org/D15397

Files:
  lib/Transforms/Scalar/EarlyCSE.cpp
  test/Transforms/EarlyCSE/basic.ll

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