[Bug tree-optimization/80218] New: [6/7 Regression] tree-call-cdce does not update block frequencies

["rsandifo at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80218

            Bug ID: 80218
           Summary: [6/7 Regression] tree-call-cdce does not update block
                    frequencies
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rsandifo at gcc dot gnu.org
  Target Milestone: ---

tree-call-cdce.c updates the edge probabilities and counts, but doesn't do
anything to the block frequencies or counts.  This causes the register
allocator to treat the fallback errno-setting calls as being much hotter than
they really are.

Although the bug goes back to at least GCC 5, GCC 6 patch r230488 caused us to
use the code much more often than previously.  In an internal benchmark, we
were seeing spills in hot code that were confined to the "error" path in GCC 5
but are on the hot path in GCC 6 and later.  I think this therefore counts as a
GCC 6 regression.