https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65963
Bug ID: 65963
Summary: Missed vectorization of loads strided with << when
equivalent * succeeds
Product: gcc
Version: 5.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: alalaw01 at gcc dot gnu.org
Target Milestone: ---
This testcase does not vectorize at -O3 on x86_64/-mavx or AArch64:
void
loop (int *in, int *out)
{
for (int i = 0; i < 256; i++) {
out[i] = in[i << 1] + 7;
}
}
-fdump-tree-vect-details reveals:
Creating dr for *_12
analyze_innermost: failed: evolution of base is not affine.
base_address:
offset from base address:
constant offset from base address:
step:
aligned to:
base_object: *_12
However, this testcase succeeds:
void
loop (int *in, int *out)
{
for (int i = 0; i < 256; i++) {
out[i] = in[i * 2] + 7;
}
}
The relevant extract of -fdump-tree-vect-details showing:
Creating dr for *_12
analyze_innermost: success.
base_address: in_11(D)
offset from base address: 0
constant offset from base address: 0
step: 8
aligned to: 256
base_object: *in_11(D)
Access function 0: {0B, +, 8}_1
The only difference is the multiplication:
$ diff splice{,2}.c.131t.ifcvt
27c27
< _8 = i_19 * 2;
---
> _8 = i_19 << 1;
$
