[PATCH] [MBP] Don't outline short optional branches

[Daniel Jasper]

Hi chandlerc,

With the option -outline-optional-branches, LLVM will place optional branches out of line (more details on r231230).

With this patch, this is not done for short optional branches. An short optional branches is a branch is a single block with an instruction count below a certain threshold (defaulting to 3). Still everything is guarded under -outline-optional-branches).

Outlining a short branch can't significantly improve code locality. It can however decrease performance because of the additional jmp and in cases where the optional branch is hot. This fixes a compile time regression I have observed in a benchmark.

http://reviews.llvm.org/D8108

Files:
  lib/CodeGen/MachineBlockPlacement.cpp
  test/CodeGen/X86/code_placement_outline_optional_branches.ll

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