https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102756
Bug ID: 102756
Summary: [12 Regression] Vectorizer change creates poor code
for c-c++-common/torture/vector-compare-2.c
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: law at gcc dot gnu.org
Target Milestone: ---
The visium-elf port is a bit broken in that any code which calls abort will
fail to link. This has turned out to be useful in that it has pointed out
cases where the quality of our code generation has suffered.
The change to turn on the vectorizer by default at -O2 is yet another example.
c-c++-common/torture/vector-compare-2.c before the vectorizer change compiled
down to this code at -O2:
.file "j.c"
.text
.align 4
.p2align 8
.global foo
.type foo, @function
foo:
moviu r9,65535
movil r9,65533
write.l (r1),r9
write.l 1(r1),r9
write.l 2(r1),r9
bra tr,r21,r0 ;return
write.l 3(r1),r9
.size foo, .-foo
.section .text.startup,"ax",@progbits
.align 4
.p2align 8
.global main
.type main, @function
main:
bra tr,r21,r0 ;return
moviq r1,0 ;movsi r J
.size main, .-main
.ident "GCC: (GNU) 12.0.0 20211008 (experimental)"
Of particular note "main" does _not_ call abort. The optimizers have figured
everything out and realized that it should never abort.
After enabling the vectorizer at -O2 we get:
.file "j.c"
.text
.align 4
.p2align 8
.global foo
.type foo, @function
foo:
moviu r9,65535
movil r9,65533
write.l (r1),r9
write.l 1(r1),r9
write.l 2(r1),r9
bra tr,r21,r0 ;return
write.l 3(r1),r9
.size foo, .-foo
.section .text.startup,"ax",@progbits
.align 4
.p2align 8
.global main
.type main, @function
main:
subi sp,36
moviq r10,23 ;movsi r J
write.l (sp),fp
move.l fp,sp ;stack_save
add.l r8,fp,r10
lsr.l r8,r8,4
asl.l r8,r8,4
moviu r9,65535
write.l 1(sp),r21
movil r9,65533
write.l (r8),r9
write.l 1(r8),r9
write.l 2(r8),r9
write.l 3(r8),r9
move.l r10,r8
moviq r8,16 ;movsi r J
add.l r7,r10,r8
.L5:
read.l r8,(r10)
cmp.l r8,r9
brr ne,.L8
addi r10,4
cmp.l r10,r7
brr ne,.L5
moviq r1,0 ;movsi r J
read.l fp,(sp)
read.l r21,1(sp)
bra tr,r21,r0 ;return
addi sp,36 ;stack pop
.L8:
moviu r10,%u abort
movil r10,%l abort
bra tr,r10,r21
nop ;call
.size main, .-main
.ident "GCC: (GNU) 12.0.0 20211008 (experimental)"
Note how there's a call to abort starting at the label .L8. And more generally
the code in "main" is considerably larger and more complex.
This is a code quality regression.
