[PATCH] Optimize vec_splats of vec_extract for V2DI/V2DF (PR target/99293)

[Michael Meissner <meissner@linux.ibm.com>]

This patch optimizes cases like:

	vector double v1, v2;
	/* ... */
	v2 = vec_splats (vec_extract (v1, 0);	/* or  */
	v2 = vec_splats (vec_extract (v1, 1);

Previously:

	vector long long
	splat_dup_l_0 (vector long long v)
	{
	  return __builtin_vec_splats (__builtin_vec_extract (v, 0));
	}

would generate:

        mfvsrld 9,34
        mtvsrdd 34,9,9
        blr

With this patch, GCC generates:

        xxpermdi 34,34,34,3
	blr

2023-07-10  Michael Meissner  <meissner@linux.ibm.com>

gcc/

	PR target/99293
	* gcc/config/rs6000/vsx.md (vsx_splat_extract_<mode>): New combiner
	insn.

gcc/testsuite/

	PR target/108958
	* gcc.target/powerpc/pr99293.c: New test.
	* gcc.target/powerpc/builtins-1.c: Update insn count.
---
 gcc/config/rs6000/vsx.md                      | 18 ++++++
 gcc/testsuite/gcc.target/powerpc/builtins-1.c |  2 +-
 gcc/testsuite/gcc.target/powerpc/pr99293.c    | 55 +++++++++++++++++++
 3 files changed, 74 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/gcc.target/powerpc/pr99293.c

diff --git a/gcc/config/rs6000/vsx.md b/gcc/config/rs6000/vsx.md
index 0c269e4e8d9..d34c3b21abe 100644
--- a/gcc/config/rs6000/vsx.md
+++ b/gcc/config/rs6000/vsx.md
@@ -4600,6 +4600,24 @@ (define_insn "vsx_splat_<mode>_mem"
   "lxvdsx %x0,%y1"
   [(set_attr "type" "vecload")])
 
+;; Optimize SPLAT of an extract from a V2DF/V2DI vector with a constant element
+(define_insn "*vsx_splat_extract_<mode>"
+  [(set (match_operand:VSX_D 0 "vsx_register_operand" "=wa")
+	(vec_duplicate:VSX_D
+	 (vec_select:<VEC_base>
+	  (match_operand:VSX_D 1 "vsx_register_operand" "wa")
+	  (parallel [(match_operand 2 "const_0_to_1_operand" "n")]))))]
+  "VECTOR_MEM_VSX_P (<MODE>mode)"
+{
+  int which_word = INTVAL (operands[2]);
+  if (!BYTES_BIG_ENDIAN)
+    which_word = 1 - which_word;
+
+  operands[3] = GEN_INT (which_word ? 3 : 0);
+  return "xxpermdi %x0,%x1,%x1,%3";
+}
+  [(set_attr "type" "vecperm")])
+
 ;; V4SI splat support
 (define_insn "vsx_splat_v4si"
   [(set (match_operand:V4SI 0 "vsx_register_operand" "=wa,wa")
diff --git a/gcc/testsuite/gcc.target/powerpc/builtins-1.c b/gcc/testsuite/gcc.target/powerpc/builtins-1.c
index 28cd1aa6b1a..98783668bce 100644
--- a/gcc/testsuite/gcc.target/powerpc/builtins-1.c
+++ b/gcc/testsuite/gcc.target/powerpc/builtins-1.c
@@ -1035,4 +1035,4 @@ foo156 (vector unsigned short usa)
 /* { dg-final { scan-assembler-times {\mvmrglb\M} 3 } } */
 /* { dg-final { scan-assembler-times {\mvmrgew\M} 4 } } */
 /* { dg-final { scan-assembler-times {\mvsplth|xxsplth\M} 4 } } */
-/* { dg-final { scan-assembler-times {\mxxpermdi\M} 44 } } */
+/* { dg-final { scan-assembler-times {\mxxpermdi\M} 42 } } */
diff --git a/gcc/testsuite/gcc.target/powerpc/pr99293.c b/gcc/testsuite/gcc.target/powerpc/pr99293.c
new file mode 100644
index 00000000000..e5f44bd7346
--- /dev/null
+++ b/gcc/testsuite/gcc.target/powerpc/pr99293.c
@@ -0,0 +1,55 @@
+/* { dg-require-effective-target powerpc_p8vector_ok } */
+/* { dg-options "-O2 -mpower8-vector" } */
+
+/* Test for PR 99263, which wants to do:
+	__builtin_vec_splats (__builtin_vec_extract (v, n))
+
+   where v is a V2DF or V2DI vector and n is either 0 or 1.  Previously the GCC
+   compiler would do a direct move to the GPR registers to select the item and a
+   direct move from the GPR registers to do the splat.
+
+   Before the patch, splat_dup_ll_0 or splat_dup_dbl_0 below would generate:
+
+        mfvsrld 9,34
+        mtvsrdd 34,9,9
+        blr
+
+   and now it generates:
+
+        xxpermdi 34,34,34,3
+        blr  */
+
+#include <altivec.h>
+
+vector long long
+splat_dup_ll_0 (vector long long v)
+{
+  /* xxpermdi 34,34,34,3 */
+  return __builtin_vec_splats (vec_extract (v, 0));
+}
+
+vector double
+splat_dup_dbl_0 (vector double v)
+{
+  /* xxpermdi 34,34,34,3 */
+  return __builtin_vec_splats (vec_extract (v, 0));
+}
+
+vector long long
+splat_dup_ll_1 (vector long long v)
+{
+  /* xxpermdi 34,34,34,0 */
+  return __builtin_vec_splats (vec_extract (v, 1));
+}
+
+vector double
+splat_dup_dbl_1 (vector double v)
+{
+  /* xxpermdi 34,34,34,0 */
+  return __builtin_vec_splats (vec_extract (v, 1));
+}
+
+/* { dg-final { scan-assembler-times "xxpermdi" 4 } } */
+/* { dg-final { scan-assembler-not   "mfvsrd"     } } */
+/* { dg-final { scan-assembler-not   "mfvsrld"    } } */
+/* { dg-final { scan-assembler-not   "mtvsrdd"    } } */
-- 
2.41.0


-- 
Michael Meissner, IBM
PO Box 98, Ayer, Massachusetts, USA, 01432
email: meissner@linux.ibm.com