[PATCH v2] x86: correct and improve "*vec_dupv2di"

[Jan Beulich <jbeulich@suse.com>]

The input constraint for the %vmovddup alternative was wrong, as the
upper 16 XMM registers require AVX512VL to be used with this insn. To
compensate, introduce a new alternative permitting all 32 registers, by
broadcasting to the full 512 bits in that case if AVX512VL is not
available.

gcc/

	* config/i386/sse.md (vec_dupv2di): Correct %vmovddup input
	constraint. Add new AVX512F alternative.
---
Strictly speaking the new alternative could be enabled from AVX2
onwards, but vmovddup can frequently be a shorter encoding (VEX2 vs
VEX3).

It was suggested that the previously flawed %vmovddup alternative could
use "xm" as source constraint. But then its destination would better also
use "x", I think?
---
v2: Use "* return ..." form. Set "mode" to XI for new alternative
    without AVX512VL.

--- a/gcc/config/i386/sse.md
+++ b/gcc/config/i386/sse.md
@@ -26033,19 +26033,35 @@
 	   (symbol_ref "true")))])
 
 (define_insn "*vec_dupv2di"
-  [(set (match_operand:V2DI 0 "register_operand"     "=x,v,v,x")
+  [(set (match_operand:V2DI 0 "register_operand"     "=x,v,v,v,x")
 	(vec_duplicate:V2DI
-	  (match_operand:DI 1 "nonimmediate_operand" " 0,Yv,vm,0")))]
+	  (match_operand:DI 1 "nonimmediate_operand" " 0,Yv,vm,Yvm,0")))]
   "TARGET_SSE"
   "@
    punpcklqdq\t%0, %0
    vpunpcklqdq\t{%d1, %0|%0, %d1}
+   * return TARGET_AVX512VL ? \"vpbroadcastq\t{%1, %0|%0, %1}\" : \"vpbroadcastq\t{%1, %g0|%g0, %1}\";
    %vmovddup\t{%1, %0|%0, %1}
    movlhps\t%0, %0"
-  [(set_attr "isa" "sse2_noavx,avx,sse3,noavx")
-   (set_attr "type" "sselog1,sselog1,sselog1,ssemov")
-   (set_attr "prefix" "orig,maybe_evex,maybe_vex,orig")
-   (set_attr "mode" "TI,TI,DF,V4SF")])
+  [(set_attr "isa" "sse2_noavx,avx,avx512f,sse3,noavx")
+   (set_attr "type" "sselog1,sselog1,ssemov,sselog1,ssemov")
+   (set_attr "prefix" "orig,maybe_evex,evex,maybe_vex,orig")
+   (set (attr "mode")
+	(cond [(and (eq_attr "alternative" "2")
+		    (match_test "!TARGET_AVX512VL"))
+		 (const_string "XI")
+	       (eq_attr "alternative" "3")
+		 (const_string "DF")
+	       (eq_attr "alternative" "4")
+		 (const_string "V4SF")
+	      ]
+	      (const_string "TI")))
+   (set (attr "enabled")
+	(if_then_else
+	  (eq_attr "alternative" "2")
+	  (symbol_ref "TARGET_AVX512VL
+		       || (TARGET_AVX512F && !TARGET_PREFER_AVX256)")
+	  (const_string "*")))])
 
 (define_insn "avx2_vbroadcasti128_<mode>"
   [(set (match_operand:VI_256 0 "register_operand" "=x,v,v")