https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95102
Bug ID: 95102
Summary: missed if-conversion
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: rtl-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: rguenth at gcc dot gnu.org
Target Milestone: ---
If you rewrite gcc.target/i386/pr54855-9.c to a form GIMPLE looks like after
some PRE you end up with
typedef float vec __attribute__((vector_size(16)));
vec
foo (vec x, float a)
{
if (!(x[0] < a))
x[0] = a;
return x;
}
which is no longer recognized as the same and emits
foo:
.LFB0:
.cfi_startproc
comiss %xmm0, %xmm1
ja .L2
movss %xmm1, %xmm0
.L2:
ret
instead of
foo:
.LFB1:
.cfi_startproc
minss %xmm1, %xmm0
ret
this is because RTL if-conversion does not recognize
7: r86:SF=vec_select(r84:V4SF,parallel)
8: flags:CCFP=cmp(r85:SF,r86:SF)
REG_DEAD r86:SF
9: pc={(flags:CCFP>0)?L14:pc}
REG_DEAD flags:CCFP
REG_BR_PROB 536870916
10: NOTE_INSN_BASIC_BLOCK 3
12: r84:V4SF=vec_merge(vec_duplicate(r85:SF),r84:V4SF,0x1)
REG_DEAD r85:SF
14: L14:
15: NOTE_INSN_BASIC_BLOCK 4
20: xmm0:V4SF=r84:V4SF
the form it does recognize is
8: r82:SF=vec_select(r84:V4SF,parallel)
9: flags:CCFP=cmp(r85:SF,r82:SF)
10: pc={(flags:CCFP>0)?L28:pc}
REG_DEAD flags:CCFP
REG_BR_PROB 536870916
28: L28:
14: NOTE_INSN_BASIC_BLOCK 3
5: r85:SF=r82:SF
REG_DEAD r82:SF
15: L15:
16: NOTE_INSN_BASIC_BLOCK 4
18: r87:V4SF=vec_merge(vec_duplicate(r85:SF),r84:V4SF,0x1)
