https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78396
Bug ID: 78396
Summary: [7 regression] gcc.dg/vect/bb-slp-cond-1.c FAILs after
fix for PR77848
Product: gcc
Version: 7.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: wschmidt at gcc dot gnu.org
Target Milestone: ---
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77848 identified a case where
if-conversion modified a loop that was not subsequently vectorized, with the
resulting code being significantly worse than without if-conversion. Since
if-conversion has no cost model, this was resolved by requiring loop versioning
for all if-converted loops unless if-conversion was specifically requested.
There was one bit of fallout from this, as gcc.dg/vect/bb-slp-cond-1.c now
fails. This test expected if-converted input that the BB vectorizer would be
able to handle after the loop vectorizer failed on it.
There are two ways this can be resolved:
- Improve the data dependence analysis in the loop vectorizer; or
- Teach the basic block vectorizer to if-convert PHIs in otherwise
straight-line code.
