[Bug rtl-optimization/68695] [6 Regression] Performance regression related to ssa patch / ifcvt

["law at redhat dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68695

Jeffrey A. Law <law at redhat dot com> changed:

           What    |Removed                     |Added
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           Priority|P1                          |P2
                 CC|                            |law at redhat dot com

--- Comment #24 from Jeffrey A. Law <law at redhat dot com> ---
I think one could easily argue here that the only reason we got good code
before Alex's change is because the copyrename pass was buggy.

Given something like this:

  # i_1 = PHI <x_3(D)(2), a_5(D)(3)>

Where x & a are parameters and i is a local, all of type int.  The copyrename
pass would ignore the fact that x & a were promoted to DImode while i was
SImode

Alex's work exposed this as problematical in general and the suggested fix was
to not coalesce with the promoted modes were different.

I don't think this deserves to be a release blocker, but I do think we can
continue to look at either improving things on the RTL side, or finding a safe
set of cases where we can coalesce even when the promotions are different.