i386: Improve code generation for vector __builtin_signbit (x.x[i]) ?…

… -1 : 0 [PR112816]

On the testcase I've recently fixed I've noticed bad code generation,
we emit
        pxor    %xmm1, %xmm1
        psrld   $31, %xmm0
        pcmpeqd %xmm1, %xmm0
        pcmpeqd %xmm1, %xmm0
or
        vpxor   %xmm1, %xmm1, %xmm1
        vpsrld  $31, %xmm0, %xmm0
        vpcmpeqd        %xmm1, %xmm0, %xmm0
        vpcmpeqd        %xmm1, %xmm0, %xmm2
rather than
        psrad   $31, %xmm2
or
        vpsrad  $31, %xmm1, %xmm2
The following patch fixes that using a combiner splitter.

2023-12-05  Jakub Jelinek  <jakub@redhat.com>

	PR target/112816
	* config/i386/sse.md ((eq (eq (lshiftrt x elt_bits-1) 0) 0)): New
	splitter to turn psrld $31; pcmpeq; pcmpeq into psrad $31.

	* gcc.target/i386/pr112816.c: New test.

gcc/config/i386/sse.md

@@ -16614,6 +16614,18 @@
   DONE;
 })
 
+(define_split
+  [(set (match_operand:VI248_AVX2 0 "register_operand")
+        (eq:VI248_AVX2
+	  (eq:VI248_AVX2
+	    (lshiftrt:VI248_AVX2
+	      (match_operand:VI248_AVX2 1 "register_operand")
+	      (match_operand:SI 2 "const_int_operand"))
+	    (match_operand:VI248_AVX2 3 "const0_operand"))
+	  (match_operand:VI248_AVX2 4 "const0_operand")))]
+  "INTVAL (operands[2]) == GET_MODE_PRECISION (<ssescalarmode>mode) - 1"
+  [(set (match_dup 0) (ashiftrt:VI248_AVX2 (match_dup 1) (match_dup 2)))])
+
 (define_expand "rotlv1ti3"
   [(set (match_operand:V1TI 0 "register_operand")
 	(rotate:V1TI

gcc/testsuite/gcc.target/i386/pr112816.c

@@ -0,0 +1,27 @@
+/* PR target/112816 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -mno-avx512f -masm=att" } */
+/* { dg-final { scan-assembler-times "psrad\t\\\$31," 2 } } */
+/* { dg-final { scan-assembler-not "pcmpeqd\t" } } */
+
+#define N 4
+struct S { float x[N]; };
+struct T { int x[N]; };
+
+__attribute__((target ("no-sse3,sse2"))) struct T
+foo (struct S x)
+{
+  struct T res;
+  for (int i = 0; i < N; ++i)
+    res.x[i] = __builtin_signbit (x.x[i]) ? -1 : 0;
+  return res;
+}
+
+__attribute__((target ("avx2"))) struct T
+bar (struct S x)
+{
+  struct T res;
+  for (int i = 0; i < N; ++i)
+    res.x[i] = __builtin_signbit (x.x[i]) ? -1 : 0;
+  return res;
+}