[all-commits] [llvm/llvm-project] 94faad: [llvm][CodeGen] Machine Function Splitter

[Snehasish Kumar via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: 94faadaca4e1704f674d2e9d4a1d25643b9ca52c
      https://github.com/llvm/llvm-project/commit/94faadaca4e1704f674d2e9d4a1d25643b9ca52c
  Author: Snehasish Kumar <snehasishk at google.com>
  Date:   2020-08-28 (Fri, 28 Aug 2020)

  Changed paths:
    A llvm/include/llvm/CodeGen/BasicBlockSectionUtils.h
    M llvm/include/llvm/CodeGen/CommandFlags.h
    M llvm/include/llvm/CodeGen/MachineFunction.h
    M llvm/include/llvm/CodeGen/Passes.h
    M llvm/include/llvm/InitializePasses.h
    M llvm/include/llvm/Target/TargetOptions.h
    M llvm/lib/CodeGen/BasicBlockSections.cpp
    M llvm/lib/CodeGen/CMakeLists.txt
    M llvm/lib/CodeGen/CommandFlags.cpp
    A llvm/lib/CodeGen/MachineFunctionSplitter.cpp
    M llvm/lib/CodeGen/TargetPassConfig.cpp
    A llvm/test/CodeGen/X86/machine-function-splitter.ll

  Log Message:
  -----------
  [llvm][CodeGen] Machine Function Splitter

We introduce a codegen optimization pass which splits functions into hot and cold
parts. This pass leverages the basic block sections feature recently
introduced in LLVM from the Propeller project. The pass targets
functions with profile coverage, identifies cold blocks and moves them
to a separate section. The linker groups all cold blocks across
functions together, decreasing fragmentation and improving icache and
itlb utilization.

We evaluated the Machine Function Splitter pass on clang bootstrap and
SPECInt 2017.

For clang bootstrap we observe a mean 2.33% runtime improvement with a
~32% reduction in itlb and stlb misses. Additionally, L1 icache misses
reduced by 9.5% while L2 instruction misses reduced by 20%.

For SPECInt we report the change in IntRate the C/C++
benchmarks. All benchmarks apart from mcf and x264 improve, on average
by 0.6% with the max for deepsjeng at 1.6%.

Benchmark		% Change
500.perlbench_r		 0.78
502.gcc_r		 0.82
505.mcf_r		-0.30
520.omnetpp_r		 0.18
523.xalancbmk_r		 0.37
525.x264_r		-0.46
531.deepsjeng_r		 1.61
541.leela_r		 0.83
557.xz_r		 0.15

Differential Revision: https://reviews.llvm.org/D85368