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Turn on the new pass manager by default

Authored by aeubanks on Jan 25 2021, 11:00 AM.

Description

Turn on the new pass manager by default

This turns on the new pass manager by default for the optimization pipeline in
Clang and ThinLTO in various LLD backends. This also makes uses of `opt
-instcombine` use the new pass manager (unless specifically opted out).

This does not affect the backend target-dependent codegen pipeline.

If this causes regressions, you can opt out of the new pass manager
either via the -DENABLE_EXPERIMENTAL_NEW_PASS_MANAGER=OFF CMake flag
while building LLVM, or via various compiler flags, e.g.
-flegacy-pass-manager for Clang or -Wl,--lto-legacy-pass-manager for
ELF LLD. Please file bugs for any regressions.

Major differences:

  • The inliner works slightly differently
  • -O1 does some amount of inlining
  • LCSSA and LoopSimplify are run before all loop passes
  • Loop unswitching is implemented slightly differently
  • A new SpeculateAroundPHIs pass is added to the pipeline

https://lists.llvm.org/pipermail/llvm-dev/2021-January/148098.html

Reviewed By: asbirlea, ychen, MaskRay, echristo

Differential Revision: https://reviews.llvm.org/D95380

Details

Committed
aeubanksFeb 3 2021, 2:37 PM
Reviewer
asbirlea
Differential Revision
D95380: Turn on the new pass manager by default
Parents
rGb15cbaf5a03d: PR49020: Diagnose brace elision in designated initializers in C++.
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