[Bug target/104610] memcmp () == 0 can be optimized better for avx512f

["crazylht at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104610

--- Comment #8 from Hongtao.liu <crazylht at gmail dot com> ---
Created attachment 52495
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=52495&action=edit
untested patch.

With the patch, it exposes one potential issue related to dse(or
ix86_gen_scratch_sse_rtx usage). in dse1, it try to replace load insn with
equivalent value, but the inserted new insns(insn 45, insn 44, insn 46) will
set xmm31, but dse is not aware of that, and xmm31 is alive and will be used by
insn 10 which is exactly after new added insns, and it breaks data flow.

and i think for i386 part, maybe we shouldn't use ix86_gen_scratch_sse_rtx in
ix86_expand_vector_move which is called by emit_move_insn and used in many
pre_reload passes, it may break data flow if there're other explicit hard
register used. 

dump before vs after dse

+(insn 45 8 44 2 (set (reg:DI 91)
+        (const_int 4855531112742205610 [0x43624fd242db38aa]))
"gcc/testsuite/gcc.target/i386/avx512f-typecast-1.c":48:8 80 {*movdi_internal}
+     (nil))
+(insn 44 45 46 2 (set (reg:V4DI 67 xmm31)
+        (vec_duplicate:V4DI (reg:DI 91)))
"gcc/testsuite/gcc.target/i386/avx512f-typecast-1.c":48:8 7768
{*avx512vl_vec_dup_gprv4di}
+     (expr_list:REG_DEAD (reg:DI 91)
+        (nil)))
+(insn 46 44 10 2 (set (reg:OI 90)
+        (reg:OI 67 xmm31))
"gcc/testsuite/gcc.target/i386/avx512f-typecast-1.c":48:8 78
{*movoi_internal_avx}
+     (expr_list:REG_EQUAL (const_wide_int
0x43624fd242db38aa43624fd242db38aa43624fd242db38aa43624fd242db38aa)
         (nil)))
(insn 10 46 13 2 (set (mem/j/c:V16SF (plus:DI (reg/f:DI 19 frame)
                 (const_int -128 [0xffffffffffffff80])) [4 bd.x+0 S64 A512])
         (reg:V16SF 67 xmm31))
"gcc/testsuite/gcc.target/i386/avx512f-typecast-1.c":48:8 1707
{movv16sf_internal}
      (expr_list:REG_DEAD (reg:V16SF 67 xmm31)
         (nil)))
 (insn 13 10 14 2 (set (reg:OI 86 [ MEM <char[1:64]> [(void *)&bd] ])
-        (mem/c:OI (plus:DI (reg/f:DI 19 frame)
-                (const_int -128 [0xffffffffffffff80])) [0 MEM <char[1:64]>
[(void *)&bd]+0 S32 A512]))
"gcc/testsuite/gcc.target/i386/avx512f-typecast-1.c":49:7 78
{*movoi_internal_avx}
-     (nil))
+        (reg:OI 90)) "gcc/testsuite/gcc.target/i386/avx512f-typecast-1.c":49:7
78 {*movoi_internal_avx}
+     (expr_list:REG_DEAD (reg:OI 90)
+        (nil)))