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.
- 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