https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125672
Bug ID: 125672
Summary: Jump threading hurts conditional select formation
Product: gcc
Version: 16.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: ktkachov at gcc dot gnu.org
Target Milestone: ---
Created attachment 64676
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=64676&action=edit
Testcase demonstrating excessive conditional branches
Looking at SPEC2026 performance, the astcenc performance improves by ~14% on an
aarch64 machine if compiled with -fno-thread-jumps with -Ofast -flto.
The problem seems like a function with many operations that should be converted
to FP CSEL operations (FCSEL on aarch64) but jump threading jumbles up the
basic blocks and phiopt fails to handle them.
I'm attaching a reproducer that shows the effect with and without
-fno-thread-jumps
