http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60989
Bug ID: 60989
Summary: automatic increase of global array for vectorization
doesn't work due to flag_section_anchors==0
Product: gcc
Version: 4.9.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: andi-gcc at firstfloor dot org
Target x86_64-linux
Following simple test case:
#define N 64
#define ALIGN // __attribute__((aligned(64)))
int a[N] ALIGN;
int b[N] ALIGN;
main()
{
int i;
for (i = 0; i < N; i++)
a[i] = b[i] + 1;
}
If I leave the ALIGN commented out I get really horrible manual alignment
prologue code like
-O3 -mavx512f
.cfi_startproc
movl $a, %eax
andl $63, %eax
shrq $2, %rax
negq %rax
andl $15, %eax
je .L7
movl b(%rip), %edi
cmpl $1, %eax
leal 1(%rdi), %edx
movl %edx, a(%rip)
je .L8
...
lots of repeats upto 63
With ALIGN it's a nice short perfectly vectorized loop.
It seems the automatic alignment of global variables doesn't work anymore.
I checked the increase_alignment/ipa_increase_alignment pass in
tree-vectorize.c and both don't run because flag_section_anchors is 0 in the
gate.
I'm not fully sure what the flag means?
