[PATCH] D119879: [DSE] Model reads after returning explicitly in MemSSA.

[Florian Hahn via Phabricator via llvm-commits]

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This allows removing the post-dominance/CFG checks, after the full read
check.

This catches a tiny amount of additional cases, because we are not
restricted to the CFG traversal limit.

For MultiSource/SPEC2006/SPEC2017 on X86 with -O3:

Program                                       base    patch   diff
test-suite...Source/Benchmarks/sim/sim.test      4.00    6.00 50.0%
test-suite...epsjeng_r/531.deepsjeng_r.test     44.00   48.00  9.1%
test-suite...T2006/445.gobmk/445.gobmk.test     46.00   47.00  2.2%
test-suite...ate/525.x264_r/525.x264_r.test    400.00  402.00  0.5%
test-suite...7rate/502.gcc_r/502.gcc_r.test   1241.00 1246.00  0.4%
test-suite...-typeset/consumer-typeset.test    766.00  767.00  0.1%
test-suite...6.blender_r/526.blender_r.test   3743.00 3745.00  0.1%

Compile-time wise this is mostly neutral
https://llvm-compile-time-tracker.com/compare.php?from=dd145f953db3dafbc019f1d3783bb4f09a28af92&to=55c8c0b5ec1257c46b004e6247c327b8677dc6cc&stat=instructions

See D119760 <https://reviews.llvm.org/D119760>.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D119879

Files:
  llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
  llvm/test/Other/new-pm-lto-defaults.ll

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