https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81082
Bug ID: 81082
Summary: [7 Regression] Failure to vectorise after
reassociating index computation
Product: gcc
Version: unknown
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: ---
After the fix for PR66313 (r248771), we no longer vectorise:
int
f (int *x, int b1, int b2, int b3)
{
int foo = 0;
for (int i1 = 0; i1 < b1; ++i1)
for (int i2 = 0; i2 < b2; ++i2)
for (int i3 = 0; i3 < b3; ++i3)
foo += x[i1 * b2 * b3 + i2 * b3 + (i3 - 1)];
return foo;
}
We now convert all the arithmetic in the [...] to unsigned int
and reassociate it so that the "- 1" is applied last. We then assume
that the overflow in this subtraction is well-defined and that the
&x[...] might not be linear for the inner loop.
