[Bug target/94962] Suboptimal AVX2 code for _mm256_zextsi128_si256(_mm_set1_epi8(-1))

[crazylht at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94962

Hongtao.liu <crazylht at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |crazylht at gmail dot com

--- Comment #1 from Hongtao.liu <crazylht at gmail dot com> ---
redudant vmovdaq xmm0, xmm0 is generated by 
----
(insn:TI 7 6 14 2 (set (reg:V8SI 20 xmm0 [84])
        (vec_concat:V8SI (reg:V4SI 20 xmm0 [86])
            (const_vector:V4SI [
                    (const_int 0 [0]) repeated x4
                ])))
"/export/users2/liuhongt/install/gcc10_trunk/lib/gcc/x86_64-pc-linux-gnu/10.0.1/include/avxintrin.h":770:20
5296 {avx_vec_concatv8si}
     (expr_list:REG_EQUIV (const_vector:V8SI [
                (const_int -1 [0xffffffffffffffff]) repeated x4
                (const_int 0 [0]) repeated x4
            ])
        (nil)))
-----

could be eliminated if src operand has same regno as dest operand.

---
diff --git a/gcc/config/i386/sse.md b/gcc/config/i386/sse.md
index 7a7ecd4be87..4ff4cf55f74 100644
--- a/gcc/config/i386/sse.md
+++ b/gcc/config/i386/sse.md
@@ -21123,6 +21123,9 @@
        }
     case 2:
     case 3:
+      if (register_operand (operands[1], <ssehalfvecmode>MODE)
+         && REGNO (operands[1]) == REGNO (operand[0]))
+       return "";
       switch (get_attr_mode (insn))
        {
        case MODE_V16SF:
---