[InstCombine] Taking an order of magnitude longer in 12.0.0 than in 10.0.0 for some examples. #49499
Description
| Bugzilla Link | 50155 |
| Resolution | FIXED |
| Resolved on | Jun 14, 2021 16:23 |
| Version | unspecified |
| OS | Linux |
| Blocks | #48661 |
| Attachments | gzipped ir module exhibiting much slower InstCombine optimization pass. |
| CC | @aqjune,@RKSimon,@nikic,@rotateright,@tstellar |
| Fixed by commit(s) | 2cd7868 ce77909 |
Extended Description
For some functions, the --instcombine optimization takes excessively longer with llvm 12.0.0 than it does with llvm 10.0.0.
In the attached example, a run of "opt -o=out.o --instcombine test_instcomb.ir" takes 53 seconds, where it used to take around 2 seconds when version 10.0.0 was used (albeit version 12.0.0 combines more instructions).
Is there a way to mitigate this speed performance degradation when using the library interface (i.e. from C++ library API, not from the opt tool)?