[PATCH] D22143: [SimplifyCFG] Rewrite SinkThenElseCodeToEnd

[James Molloy via llvm-commits]

jmolloy created this revision.
jmolloy added reviewers: sanjoy, mcrosier.
jmolloy added a subscriber: llvm-commits.
jmolloy set the repository for this revision to rL LLVM.

The new version has several advantages:
  1) (IMNSHO) it's more readable and neater
  2) It handles loads and stores properly
  3) It can handle any number of incoming blocks rather than just two. I'll be taking advantage of this in a followup patch.

With this change we can now finally sink load-modify-store idioms such as:

    if (a)
      return *b += 3;
    else
      return *b += 4;

    =>

    %z = load i32, i32* %y
    %.sink = select i1 %a, i32 5, i32 7
    %b = add i32 %z, %.sink
    store i32 %b, i32* %y
    ret i32 %b

When this works for switches it'll be even more powerful.

Repository:
  rL LLVM

http://reviews.llvm.org/D22143

Files:
  lib/Transforms/Utils/SimplifyCFG.cpp
  test/CodeGen/ARM/avoid-cpsr-rmw.ll
  test/DebugInfo/ARM/single-constant-use-preserves-dbgloc.ll
  test/Transforms/SimplifyCFG/AArch64/prefer-fma.ll
  test/Transforms/SimplifyCFG/sink-common-code.ll

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