[pushed] aarch64: Define TARGET_INSN_COST

[pushed] aarch64: Define TARGET_INSN_COST

[Richard Sandiford]

This patch adds a bare-bones TARGET_INSN_COST.  See the comment
in the patch for the rationale.

This change is needed to avoid a regression with a later change.

Tested on aarch64-linux-gnu & pushed.

Richard


gcc/
	* config/aarch64/aarch64.cc (aarch64_insn_cost): New function.
	(TARGET_INSN_COST): Define.
---
 gcc/config/aarch64/aarch64.cc | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index a28b66acf6a..4cbfa42cb3c 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -15541,6 +15541,28 @@ aarch64_memory_move_cost (machine_mode mode, reg_class_t rclass_i, bool in)
 	  : aarch64_tune_params.memmov_cost.store_int);
 }
 
+/* Implement TARGET_INSN_COST.  We have the opportunity to do something
+   much more productive here, such as using insn attributes to cost things.
+   But we don't, not yet.
+
+   The main point of this current definition is to make calling insn_cost
+   on one instruction equivalent to calling seq_cost on a sequence that
+   contains only that instruction.  The default definition would instead
+   only look at SET_SRCs, ignoring SET_DESTs.
+
+   This ensures that, for example, storing a 128-bit zero vector is more
+   expensive than storing a 128-bit vector register.  A move of zero
+   into a 128-bit vector register followed by multiple stores of that
+   register is then cheaper than multiple stores of zero (which would
+   use STP of XZR).  This in turn allows STPs to be formed.  */
+static int
+aarch64_insn_cost (rtx_insn *insn, bool speed)
+{
+  if (rtx set = single_set (insn))
+    return set_rtx_cost (set, speed);
+  return pattern_cost (PATTERN (insn), speed);
+}
+
 /* Implement TARGET_INIT_BUILTINS.  */
 static void
 aarch64_init_builtins ()
@@ -28399,6 +28421,9 @@ aarch64_libgcc_floating_mode_supported_p
 #undef TARGET_RTX_COSTS
 #define TARGET_RTX_COSTS aarch64_rtx_costs_wrapper
 
+#undef TARGET_INSN_COST
+#define TARGET_INSN_COST aarch64_insn_cost
+
 #undef TARGET_SCALAR_MODE_SUPPORTED_P
 #define TARGET_SCALAR_MODE_SUPPORTED_P aarch64_scalar_mode_supported_p
 
-- 
2.25.1