-freroll-loops command line option broken

[m9710797]

Hi,

The option -freroll-loop is a documented option (https://clang.llvm.org/docs/ClangCommandLineReference.html), and Clang still accepts it. Though it doesn't seem to have any effect anymore.

It seems it got broken since the switch to the new pass manager. See here for some experiments/testcases:
https://godbolt.org/z/377dfonoj

• It still works with clang-12.
• It no longer works with clang-13.
• clang-13 with the option -flegacy-pass-manager does work.

Wouter

[xgupta]

Yeah, with opt it is working - https://godbolt.org/z/xG4ra15TK. but not running with clang - https://godbolt.org/z/T8xsv768W.

CC @aeubanks.

[aeubanks]

Ah yes it does look like it was in the legacy PM pipeline.

For the new PM we'd need a new flag in PipelineTuningOptions, then set it from the clang frontend, similar to UnrollLoops. The legacy PM put it toward the end of the function simplification pipeline.

[llvmbot]

@llvm/issue-subscribers-clang-driver

Author: Wouter Vermaelen (m9710797)

Hi,

The option -freroll-loop is a documented option (https://clang.llvm.org/docs/ClangCommandLineReference.html), and Clang still accepts it. Though it doesn't seem to have any effect anymore.

It seems it got broken since the switch to the new pass manager. See here for some experiments/testcases:
https://godbolt.org/z/377dfonoj

• It still works with clang-12.
• It no longer works with clang-13.
• clang-13 with the option -flegacy-pass-manager does work.

Wouter