AArch64: Adjust costing of by element MUL to be the same as SAME3 MUL.

The cost model is currently treating multiplication by element as being more
expensive than 3 same multiplication.  This means that if the value is on the
SIMD side we add an unneeded DUP.  If the value is on the genreg side we use the
more expensive DUP instead of fmov.

This patch corrects the costs such that the two multiplies are costed the same
which allows us to generate

        fmul    v3.4s, v3.4s, v0.s[0]

instead of

        dup     v0.4s, v0.s[0]
        fmul    v3.4s, v3.4s, v0.4s

gcc/ChangeLog:

	* config/aarch64/aarch64.c (aarch64_rtx_mult_cost): Adjust costs for mul.

gcc/testsuite/ChangeLog:

	* gcc.target/aarch64/asimd-mull-elem.c: New test.

diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
index 973c65aa4fb348450872036617362aa17310fb20..f3551a73d87c4e686540f39224985592c3c66fd1 100644 (file)
--- a/gcc/config/aarch64/aarch64.c
+++ b/gcc/config/aarch64/aarch64.c
@@ -11279,7 +11279,23 @@ aarch64_rtx_mult_cost (rtx x, enum rtx_code code, int outer, bool speed)
   op1 = XEXP (x, 1);
 
   if (VECTOR_MODE_P (mode))
-    mode = GET_MODE_INNER (mode);
+    {
+      unsigned int vec_flags = aarch64_classify_vector_mode (mode);
+      mode = GET_MODE_INNER (mode);
+      if (vec_flags & VEC_ADVSIMD)
+       {
+         /* The by-element versions of the instruction have the same costs as
+            the normal 3-vector version.  So don't add the costs of the
+            duplicate into the costs of the multiply.  We make an assumption
+            that the input to the VEC_DUPLICATE is already on the FP & SIMD
+            side.  This means costing of a MUL by element pre RA is a bit
+            optimistic.  */
+         if (GET_CODE (op0) == VEC_DUPLICATE)
+           op0 = XEXP (op0, 0);
+         else if (GET_CODE (op1) == VEC_DUPLICATE)
+           op1 = XEXP (op1, 0);
+       }
+    }
 
   /* Integer multiply/fma.  */
   if (GET_MODE_CLASS (mode) == MODE_INT)

diff --git a/gcc/testsuite/gcc.target/aarch64/asimd-mull-elem.c b/gcc/testsuite/gcc.target/aarch64/asimd-mull-elem.c
new file mode 100644 (file)
index 0000000..513721c
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/asimd-mull-elem.c
@@ -0,0 +1,21 @@
+/* { dg-do compile } */
+/* { dg-require-effective-target vect_int } */
+/* { dg-require-effective-target vect_float } */
+/* { dg-options "-Ofast" } */
+
+#include <arm_neon.h>
+
+void s_mult_i (int32_t* restrict res, int32_t* restrict a, int32_t b)
+{
+    for (int x = 0; x < 16; x++)
+      res[x] = a[x] * b;
+}
+
+void s_mult_f (float32_t* restrict res, float32_t* restrict a, float32_t b)
+{
+    for (int x = 0; x < 16; x++)
+      res[x] = a[x] * b;
+}
+
+/* { dg-final { scan-assembler-times {\s+mul\tv[0-9]+\.4s, v[0-9]+\.4s, v[0-9]+\.s\[0\]} 4 } } */
+/* { dg-final { scan-assembler-times {\s+fmul\tv[0-9]+\.4s, v[0-9]+\.4s, v[0-9]+\.s\[0\]} 4 } } */