aarch64: Don't include vec_select element in SIMD multiply cost

The Neon multiply/multiply-accumulate/multiply-subtract instructions
can take various forms - multiplying full vector registers of values
or multiplying one vector by a single element of another. Regardless
of the form used, these instructions have the same cost, and this
should be reflected by the RTL cost function.

This patch adds RTL tree traversal in the Neon multiply cost function
to match the vec_select used by the lane-referencing forms of the
instructions already mentioned. This traversal prevents the cost of
the vec_select from being added into the cost of the multiply -
meaning that these instructions can now be emitted in the combine
pass as they are no longer deemed prohibitively expensive.

gcc/ChangeLog:

2021-07-19  Jonathan Wright  <jonathan.wright@arm.com>

	* config/aarch64/aarch64.c (aarch64_strip_duplicate_vec_elt):
	Define.
	(aarch64_rtx_mult_cost): Traverse RTL tree to prevent
	vec_select cost from being added into Neon multiply cost.

gcc/testsuite/ChangeLog:

	* gcc.target/aarch64/vmul_element_cost.c: New test.

2 files changed, 119 insertions, 9 deletions

diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
index 81c002b..23829bb 100644
--- a/gcc/config/aarch64/aarch64.c
+++ b/gcc/config/aarch64/aarch64.c
@@ -12046,6 +12046,26 @@ aarch64_strip_extend (rtx x, bool strip_shift)
   return x;
 }
 
+
+/* Helper function for rtx cost calculation. Strip VEC_DUPLICATE as well as
+   any subsequent extend and VEC_SELECT from X. Returns the inner scalar
+   operand if successful, or the original expression on failure.  */
+static rtx
+aarch64_strip_duplicate_vec_elt (rtx x)
+{
+  if (GET_CODE (x) == VEC_DUPLICATE
+      && is_a<scalar_mode> (GET_MODE (XEXP (x, 0))))
+    {
+      x = XEXP (x, 0);
+      if (GET_CODE (x) == VEC_SELECT)
+	x = XEXP (x, 0);
+      else if ((GET_CODE (x) == ZERO_EXTEND || GET_CODE (x) == SIGN_EXTEND)
+	       && GET_CODE (XEXP (x, 0)) == VEC_SELECT)
+	x = XEXP (XEXP (x, 0), 0);
+    }
+  return x;
+}
+
 /* Return true iff CODE is a shift supported in combination
    with arithmetic instructions.  */
 
@@ -12114,15 +12134,11 @@ aarch64_rtx_mult_cost (rtx x, enum rtx_code code, int outer, bool speed)
       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);
+	     the normal 3-vector version.  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.  */
+	  op0 = aarch64_strip_duplicate_vec_elt (op0);
+	  op1 = aarch64_strip_duplicate_vec_elt (op1);
 	}
       cost += rtx_cost (op0, mode, MULT, 0, speed);
       cost += rtx_cost (op1, mode, MULT, 1, speed);
diff --git a/gcc/testsuite/gcc.target/aarch64/vmul_element_cost.c b/gcc/testsuite/gcc.target/aarch64/vmul_element_cost.c
new file mode 100644
index 0000000..c153775
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/vmul_element_cost.c
@@ -0,0 +1,94 @@
+/* { dg-do compile } */
+/* { dg-options "-O3" } */
+
+#include <arm_neon.h>
+
+#define TEST_MUL_UNIFORM(name, q, vectype, ts) \
+  vectype test_ ## name ## q ## _ ## ts (vectype a, vectype b, vectype c) \
+	{ \
+		vectype t0 = name ## q ## _n_ ## ts (a, c[1]); \
+		vectype t1 = name ## q ## _n_ ## ts (b, c[1]); \
+		return vmul ## q ## _ ## ts (t0, t1); \
+	}
+
+TEST_MUL_UNIFORM (vmul, , int16x4_t, s16)
+TEST_MUL_UNIFORM (vmul, , uint16x4_t, u16)
+TEST_MUL_UNIFORM (vmul, , int32x2_t, s32)
+TEST_MUL_UNIFORM (vmul, , uint32x2_t, u32)
+TEST_MUL_UNIFORM (vmul, , float32x2_t, f32)
+TEST_MUL_UNIFORM (vmul, q, int16x8_t, s16)
+TEST_MUL_UNIFORM (vmul, q, uint16x8_t, u16)
+TEST_MUL_UNIFORM (vmul, q, int32x4_t, s32)
+TEST_MUL_UNIFORM (vmul, q, uint32x4_t, u32)
+TEST_MUL_UNIFORM (vmul, q, float32x4_t, f32)
+TEST_MUL_UNIFORM (vmul, q, float64x2_t, f64)
+
+#define TEST_MLX_UNIFORM(name, q, vectype, ts) \
+  vectype test_ ## name ## q ## _ ## ts (vectype acc, vectype a, vectype b) \
+	{ \
+		acc = name ## q ## _n_ ## ts (acc, a, b[1]); \
+		return name ## q ## _n_ ## ts (acc, a, b[1]); \
+	}
+
+TEST_MLX_UNIFORM (vmla, , int16x4_t, s16)
+TEST_MLX_UNIFORM (vmla, , uint16x4_t, u16)
+TEST_MLX_UNIFORM (vmla, , int32x2_t, s32)
+TEST_MLX_UNIFORM (vmla, , uint32x2_t, u32)
+TEST_MLX_UNIFORM (vmla, , float32x2_t, f32)
+TEST_MLX_UNIFORM (vmla, q, int16x8_t, s16)
+TEST_MLX_UNIFORM (vmla, q, uint16x8_t, u16)
+TEST_MLX_UNIFORM (vmla, q, int32x4_t, s32)
+TEST_MLX_UNIFORM (vmla, q, uint32x4_t, u32)
+TEST_MLX_UNIFORM (vmla, q, float32x4_t, f32)
+
+TEST_MLX_UNIFORM (vmls, , int16x4_t, s16)
+TEST_MLX_UNIFORM (vmls, , uint16x4_t, u16)
+TEST_MLX_UNIFORM (vmls, , int32x2_t, s32)
+TEST_MLX_UNIFORM (vmls, , uint32x2_t, u32)
+TEST_MLX_UNIFORM (vmls, , float32x2_t, f32)
+TEST_MLX_UNIFORM (vmls, q, int16x8_t, s16)
+TEST_MLX_UNIFORM (vmls, q, uint16x8_t, u16)
+TEST_MLX_UNIFORM (vmls, q, int32x4_t, s32)
+TEST_MLX_UNIFORM (vmls, q, uint32x4_t, u32)
+TEST_MLX_UNIFORM (vmls, q, float32x4_t, f32)
+
+#define TEST_MUL_LONG(name, rettype, intype, ts, rs) \
+  rettype test_ ## name ## ts (intype a, intype b, intype c) \
+	{ \
+		rettype t0 = name ## ts (a, c[1]); \
+		rettype t1 = name ## ts (b, c[1]); \
+		return vqaddq ## _ ## rs (t0, t1); \
+	}
+
+TEST_MUL_LONG (vmull_n_, int32x4_t, int16x4_t, s16, s32)
+TEST_MUL_LONG (vmull_n_, uint32x4_t, uint16x4_t, u16, u32)
+TEST_MUL_LONG (vmull_n_, int64x2_t, int32x2_t, s32, s64)
+TEST_MUL_LONG (vmull_n_, uint64x2_t, uint32x2_t, u32, u64)
+
+TEST_MUL_LONG (vqdmull_n_, int32x4_t, int16x4_t, s16, s32)
+TEST_MUL_LONG (vqdmull_n_, int64x2_t, int32x2_t, s32, s64)
+
+#define TEST_MLX_LONG(name, rettype, intype, ts, rs) \
+  rettype test_ ## name ## _ ## ts (rettype acc, intype a, intype b) \
+	{ \
+		acc = name ## ts (acc, a, b[1]); \
+		return name ## ts (acc, a, b[1]); \
+	}
+
+TEST_MLX_LONG (vmlal_n_, int32x4_t, int16x4_t, s16, s32)
+TEST_MLX_LONG (vmlal_n_, uint32x4_t, uint16x4_t, u16, u32)
+TEST_MLX_LONG (vmlal_n_, int64x2_t, int32x2_t, s32, s64)
+TEST_MLX_LONG (vmlal_n_, uint64x2_t, uint32x2_t, u32, u64)
+
+TEST_MLX_LONG (vmlsl_n_, int32x4_t, int16x4_t, s16, s32)
+TEST_MLX_LONG (vmlsl_n_, uint32x4_t, uint16x4_t, u16, u32)
+TEST_MLX_LONG (vmlsl_n_, int64x2_t, int32x2_t, s32, s64)
+TEST_MLX_LONG (vmlsl_n_, uint64x2_t, uint32x2_t, u32, u64)
+
+TEST_MLX_LONG (vqdmlal_n_, int32x4_t, int16x4_t, s16, s32)
+TEST_MLX_LONG (vqdmlal_n_, int64x2_t, int32x2_t, s32, s64)
+
+TEST_MLX_LONG (vqdmlsl_n_, int32x4_t, int16x4_t, s16, s32)
+TEST_MLX_LONG (vqdmlsl_n_, int64x2_t, int32x2_t, s32, s64)
+
+/* { dg-final { scan-assembler-not "dup\\t" } } */