On Thu, Dec 31, 2015 at 1:14 AM, Uros Bizjak <[email protected]> wrote:
> On Wed, Dec 30, 2015 at 9:53 PM, H.J. Lu <[email protected]> wrote:
>> SSE vector arithmetic and logic instructions only accept aligned memory
>> operand. This patch adds vector_memory_operand and "Bm" constraint for
>> aligned SSE memory operand. They are applied to SSE any_logic patterns.
>>
>> OK for trunk and release branches if there are regressions?
>
> This patch is just papering over deeper problem, as Jakub said in the PR [1]:
>
> --q--
> GCC uses the ix86_legitimate_combined_insn target hook to disallow
> misaligned memory into certain SSE instructions.
> (subreg:V4SI (reg:TI 245 [ MEM[(const struct bitset &)FeatureEntry_21 + 8] ])
> 0)
> is not misaligned memory, it is a subreg of a pseudo register, so it is fine.
> If the replacement of the pseudo register with memory happens in some
> other pass, then it probably either should use the
> legitimate_combined_insn target hook or some other one. I think we
> have already a PR where that happens during live range shrinking.
> --/q--
>
> Please figure out where memory replacement happens. There are several
> other SSE insns (please grep the .md for "ssememalign" attribute) that
> are affected by this problem, so fixing a couple of patterns won't
> solve the problem completely.
LRA turns
insn 64 63 108 6 (set (reg:V4SI 148 [ vect__28.85 ])
(xor:V4SI (reg:V4SI 149)
(subreg:V4SI (reg:TI 147 [ MEM[(const struct bitset
&)FeatureEntry_2(D)] ]) 0))) foo.ii:26 3454 {*xorv4si3}
(expr_list:REG_DEAD (reg:V4SI 149)
(expr_list:REG_DEAD (reg:TI 147 [ MEM[(const struct bitset
&)FeatureEntry_2(D)] ])
(expr_list:REG_EQUIV (mem/c:V4SI (plus:DI (reg/f:DI 20 frame)
(const_int -16 [0xfffffffffffffff0])) [3
MEM[(unsigned int *)&D.2851]+0 S16 A128])
(nil)))))
into
(insn 64 63 108 6 (set (reg:V4SI 21 xmm0 [orig:148 vect__28.85 ] [148])
(xor:V4SI (reg:V4SI 21 xmm0 [149])
(mem:V4SI (reg/v/f:DI 4 si [orig:117 FeatureEntry ] [117])
[6 MEM[(const struct bitset &)FeatureEntry_2(D)]+0 S16 A32])))
foo.ii:26 3454 {*xorv4si3}
(expr_list:REG_EQUIV (mem/c:V4SI (plus:DI (reg/f:DI 20 frame)
(const_int -16 [0xfffffffffffffff0])) [3 MEM[(unsigned
int *)&D.2851]+0 S16 A128])
(nil)))
since
(mem:V4SI (reg/v/f:DI 4 si [orig:117 FeatureEntry ] [117]) [6
MEM[(const struct bitset &)FeatureEntry_2(D)]+0 S16 A32])))
satisfies the 'm" constraint. I don't think LRA should call
ix86_legitimate_combined_insn to validate to validate constraints on
an instruction.
> Looks like infrastructure problem to me, targets should have the last
> say on the validity of the insns.
>
We can replace 'm' constraint with 'Bm' constraint in sse.md or we
can add a new target hook, similar to ix86_legitimate_combined_insn,
to validate an instruction with hard registers.
--
H.J.
