[PATCH][AArch64] Add branch-cost to cpu tuning information.

[Matthew Wahab <matthew dot wahab at arm dot com>]

The AArch64 backend sets BRANCH_COST to be the constant value 2 for all cpus,
meaning that the compiler thinks that branches cost the same across all cpus.

This patch reworks the handling of branch costs to allow per-cpu values to be
set. The actual value of the branch-costs is unchanged as the correct values for
will need to be decided for each core.

Tested aarch64-none-linux-gnu with gcc-check.

Ok for trunk?
Matthew

2015-05-21  Matthew Wahab  <matthew.wahab@arm.com>

	* gcc/config/aarch64-protos.h (struct cpu_branch_cost): New.
        (tune_params): Add field branch_costs.
	(aarch64_branch_cost): Declare.
	* gcc/config/aarch64.c (generic_branch_cost): New.
	(generic_tunings): Set field cpu_branch_cost to generic_branch_cost.
	(cortexa53_tunings): Likewise.
	(cortexa57_tunings): Likewise.
	(thunderx_tunings): Likewise.
	(xgene1_tunings): Likewise.
	(aarch64_branch_cost): Define.
	* gcc/config/aarch64/aarch64.h (BRANCH_COST): Redefine.

diff --git a/gcc/config/aarch64/aarch64-protos.h b/gcc/config/aarch64/aarch64-protos.h
index 8676c5c..77b01fa 100644
--- a/gcc/config/aarch64/aarch64-protos.h
+++ b/gcc/config/aarch64/aarch64-protos.h
@@ -162,12 +162,20 @@ struct cpu_vector_cost
   const int cond_not_taken_branch_cost;  /* Cost of not taken branch.  */
 };
 
+/* Branch costs.  */
+struct cpu_branch_cost
+{
+  const int predictable;    /* Predictable branch or optimizing for size.  */
+  const int unpredictable;  /* Unpredictable branch or optimizing for speed.  */
+};
+
 struct tune_params
 {
   const struct cpu_cost_table *const insn_extra_cost;
   const struct cpu_addrcost_table *const addr_cost;
   const struct cpu_regmove_cost *const regmove_cost;
   const struct cpu_vector_cost *const vec_costs;
+  const struct cpu_branch_cost *const branch_costs;
   const int memmov_cost;
   const int issue_rate;
   const unsigned int fuseable_ops;
@@ -259,6 +267,8 @@ void aarch64_print_operand (FILE *, rtx, char);
 void aarch64_print_operand_address (FILE *, rtx);
 void aarch64_emit_call_insn (rtx);
 
+int aarch64_branch_cost (bool, bool);
+
 /* Initialize builtins for SIMD intrinsics.  */
 void init_aarch64_simd_builtins (void);
 
diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
index 77a641e..a020316 100644
--- a/gcc/config/aarch64/aarch64.c
+++ b/gcc/config/aarch64/aarch64.c
@@ -339,12 +339,20 @@ static const struct cpu_vector_cost xgene1_vector_cost =
 #define AARCH64_FUSE_ADRP_LDR	(1 << 3)
 #define AARCH64_FUSE_CMP_BRANCH	(1 << 4)
 
+/* Generic costs for branch instructions.  */
+static const struct cpu_branch_cost generic_branch_cost =
+{
+  2,  /* Predictable.  */
+  2   /* Unpredictable.  */
+};
+
 static const struct tune_params generic_tunings =
 {
   &cortexa57_extra_costs,
   &generic_addrcost_table,
   &generic_regmove_cost,
   &generic_vector_cost,
+  &generic_branch_cost,
   4, /* memmov_cost  */
   2, /* issue_rate  */
   AARCH64_FUSE_NOTHING, /* fuseable_ops  */
@@ -362,6 +370,7 @@ static const struct tune_params cortexa53_tunings =
   &generic_addrcost_table,
   &cortexa53_regmove_cost,
   &generic_vector_cost,
+  &generic_branch_cost,
   4, /* memmov_cost  */
   2, /* issue_rate  */
   (AARCH64_FUSE_MOV_MOVK | AARCH64_FUSE_ADRP_ADD
@@ -380,6 +389,7 @@ static const struct tune_params cortexa57_tunings =
   &cortexa57_addrcost_table,
   &cortexa57_regmove_cost,
   &cortexa57_vector_cost,
+  &generic_branch_cost,
   4, /* memmov_cost  */
   3, /* issue_rate  */
   (AARCH64_FUSE_MOV_MOVK | AARCH64_FUSE_ADRP_ADD
@@ -398,6 +408,7 @@ static const struct tune_params thunderx_tunings =
   &generic_addrcost_table,
   &thunderx_regmove_cost,
   &generic_vector_cost,
+  &generic_branch_cost,
   6, /* memmov_cost  */
   2, /* issue_rate  */
   AARCH64_FUSE_CMP_BRANCH, /* fuseable_ops  */
@@ -415,6 +426,7 @@ static const struct tune_params xgene1_tunings =
   &xgene1_addrcost_table,
   &xgene1_regmove_cost,
   &xgene1_vector_cost,
+  &generic_branch_cost,
   6, /* memmov_cost  */
   4, /* issue_rate  */
   AARCH64_FUSE_NOTHING, /* fuseable_ops  */
@@ -5361,6 +5373,19 @@ aarch64_address_cost (rtx x,
   return cost;
 }
 
+int
+aarch64_branch_cost (bool speed_p, bool predictable_p)
+{
+  /* When optimizing for speed, use the cost of unpredictable branches.  */
+  const struct cpu_branch_cost *branch_costs =
+    aarch64_tune_params->branch_costs;
+
+  if (!speed_p || predictable_p)
+    return branch_costs->predictable;
+  else
+    return branch_costs->unpredictable;
+}
+
 /* Return true if the RTX X in mode MODE is a zero or sign extract
    usable in an ADD or SUB (extended register) instruction.  */
 static bool
diff --git a/gcc/config/aarch64/aarch64.h b/gcc/config/aarch64/aarch64.h
index bf59e40..93a32f5 100644
--- a/gcc/config/aarch64/aarch64.h
+++ b/gcc/config/aarch64/aarch64.h
@@ -823,7 +823,8 @@ do {									     \
 #define TRAMPOLINE_SECTION text_section
 
 /* To start with.  */
-#define BRANCH_COST(SPEED_P, PREDICTABLE_P) 2
+#define BRANCH_COST(SPEED_P, PREDICTABLE_P) \
+  (aarch64_branch_cost (SPEED_P, PREDICTABLE_P))
 
 
 /* Assembly output.  */