[PATCH][AArch64] PR target/68696 FAIL: gcc.target/aarch64/vbslq_u64_1.c scan-assembler-times bif\tv 1

[Kyrill Tkachov]

Hi all,

The test gcc.target/aarch64/vbslq_u64_1.c started failing recently due to some tree-level changes.
This just exposed a deficiency in our xor-and-xor pattern for the vector bit-select pattern:
aarch64_simd_bsl<mode>_internal.

We now fail to match the rtx:
(set (reg:V4SI 79)
     (xor:V4SI (and:V4SI (xor:V4SI (reg:V4SI 32 v0 [ a ])
                 (reg/v:V4SI 77 [ b ]))
             (reg:V4SI 34 v2 [ mask ]))
         (reg/v:V4SI 77 [ b ])))

whereas before combine attempted:
(set (reg:V4SI 79)
     (xor:V4SI (and:V4SI (xor:V4SI (reg/v:V4SI 77 [ b ])
                 (reg:V4SI 32 v0 [ a ]))
             (reg:V4SI 34 v2 [ mask ]))
         (reg/v:V4SI 77 [ b ])))

Note that just the order of the operands of the inner XOR has changed.
This could be solved by making the second operand of the outer XOR a 4th operand
of the pattern, enforcing that it should be equal to operand 2 or 3 in the pattern
condition and performing the appropriate swapping in the output template.
However, the aarch64_simd_bsl<mode>_internal pattern is expanded to by other
places in aarch64-simd.md and updating all the callsites to add a 4th operand is
wasteful and makes them harder to understand.

Therefore this patch adds a new define_insn with the match_dup of operand 2 in
the outer XOR.  I also had to update the alternatives/constraints in the pattern
and the output template. Basically it involves swapping operands 2 and 3 around in the
constraints and output templates.

The test now combines to a single vector bfi instruction again.

Bootstrapped and tested on aarch64.

Ok for trunk?

Thanks,
Kyrill

2015-12-08  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>

     PR target/68696
     * config/aarch64/aarch64-simd.md (*aarch64_simd_bsl<mode>_alt):
     New pattern.
     (aarch64_simd_bsl<mode>_internal): Update comment to reflect
     the above.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: aarch64-bfi-vec.patch
Type: text/x-patch
Size: 1998 bytes
Desc: not available
URL: <http://gcc.gnu.org/pipermail/gcc-patches/attachments/20151208/412d2c8b/attachment.bin>