[PATCH] D30309: CodeGen: BlockPlacement: Precompute layout for chains of triangles.

[Kyle Butt via Phabricator via llvm-commits]

iteratee created this revision.
Herald added a subscriber: nemanjai.

For chains of triangles with small join blocks that can be tail duplicated, a
simple calculation of probabilities is insufficient. We treat an unhinted branch
as 50/50, but it's more likely 60/40, with a bimodal distribution. Dominating
branches are also likely to be postively correlated. A suite of Google
benchmarks bear this out. Given those 2 facts, tail-duplicating when a chain of
2 or duplication opportunities follow each other with at least balanced branch
probabilities, can be profitable.


Repository:
  rL LLVM

https://reviews.llvm.org/D30309

Files:
  lib/CodeGen/MachineBlockPlacement.cpp
  test/CodeGen/Mips/llvm-ir/ashr.ll
  test/CodeGen/Mips/llvm-ir/lshr.ll
  test/CodeGen/Mips/llvm-ir/shl.ll
  test/CodeGen/PowerPC/tail-dup-layout.ll
  test/CodeGen/X86/cmovcmov.ll

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