http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56625
Bug #: 56625 Summary: After if-conversion vectorizer doesn't recognize similar stores Classification: Unclassified Product: gcc Version: 4.8.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: tree-optimization AssignedTo: unassig...@gcc.gnu.org ReportedBy: michael.v.zolotuk...@gmail.com CC: kirill.yuk...@intel.com, michael.v.zolotuk...@gmail.com Build: 4.8.0 20130313 Created attachment 29673 --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29673 Reproducer In the following example there are two stores a[i]<-b[i] after if-conversion. void foo (double a[], double b[]) { int i; for (i = 0; i < 100; i++) { if (a[i] == 0) a[i] = b[i]*4; else a[i] = b[i]*3; } } As vectorizer knows nothing about dependencies between a and b, it needs a runtime test for it. But in the given example, vectorizer generates two runtime-tests instead of one: note: mark for run-time aliasing test between *_11 and *_8 note: mark for run-time aliasing test between *_15 and *_8 The test is attached, command line to reproduce: gcc if-conv-runtime-tests.c -O3 -c -ftree-vectorizer-verbose=15 -ftree-loop-if-convert-stores -fdump-tree-vect