We are currently running the post-ra scheduler for x86 with -O3. It is not really clear that it is worth the compile time.
X86 scheduling is a mystery that post-ra has not solved.
I ran the nightly test suite on x86_64 with LTO enabled and -O3 with and without -disable-post-ra. Code generation is 10% faster overall with -disable-post-ra, and the runtime impact varies from a 17% speedup to a 17 percent slowdown.
Below are the tests that had a more than 3% change in runtime.
I think we should disable post-ra scheduling for x86.
disable-post-ra.pdf (28 KB)