RE: [PATCH, Aarch64] Add FMA steering pass for Cortex-A57

["Thomas Preud'homme" <thomas dot preudhomme at arm dot com>]

> From: Marcus Shawcroft [mailto:marcus.shawcroft@gmail.com]
> Sent: Thursday, February 05, 2015 5:17 PM
> >
> > *** gcc/ChangeLog ***
> >
> > 2015-01-26 Thomas Preud'homme thomas.preudhomme@arm.com
> >
> >     * config.gcc: Add cortex-a57-fma-steering.o to extra_objs for
> >     aarch64-*-*.
> >     * config/aarch64/t-aarch64: Add a rule for cortex-a57-fma-steering.o.
> >     * config/aarch64/aarch64.h
> (AARCH64_FL_USE_FMA_STEERING_PASS): Define.
> >     (AARCH64_TUNE_FMA_STEERING): Likewise.
> >     * config/aarch64/aarch64-cores.def: Set
> >     AARCH64_FL_USE_FMA_STEERING_PASS for cores with dynamic
> steering of
> >     FMUL/FMADD instructions.
> >     * config/aarch64/aarch64.c (aarch64_register_fma_steering): Declare.
> >     (aarch64_override_options): Include cortex-a57-fma-steering.h.  Call
> >     aarch64_register_fma_steering () if
> AARCH64_TUNE_FMA_STEERING is true.
> >     * config/aarch64/cortex-a57-fma-steering.h: New file.
> >     * config/aarch64/cortex-a57-fma-steering.c: Likewise.
> 
> OK but wait for stage-1 to open for general development before you
> commit it please.

Done after rebasing it (context line change in aarch64.c due to new header
include and adaptation to new signature of AARCH64_CORE macro in
aarch64-cores.def).

Committed patch below:

diff --git a/gcc/config.gcc b/gcc/config.gcc
index a1df043..9fec1e8 100644
--- a/gcc/config.gcc
+++ b/gcc/config.gcc
@@ -302,7 +302,7 @@ m32c*-*-*)
 aarch64*-*-*)
 	cpu_type=aarch64
 	extra_headers="arm_neon.h arm_acle.h"
-	extra_objs="aarch64-builtins.o aarch-common.o"
+	extra_objs="aarch64-builtins.o aarch-common.o cortex-a57-fma-steering.o"
 	target_gtfiles="\$(srcdir)/config/aarch64/aarch64-builtins.c"
 	target_has_targetm_common=yes
 	;;
diff --git a/gcc/config/aarch64/aarch64-cores.def b/gcc/config/aarch64/aarch64-cores.def
index 7c285ba..dfc9cc8 100644
--- a/gcc/config/aarch64/aarch64-cores.def
+++ b/gcc/config/aarch64/aarch64-cores.def
@@ -40,7 +40,7 @@
 /* V8 Architecture Processors.  */
 
 AARCH64_CORE("cortex-a53",  cortexa53, cortexa53, 8,  AARCH64_FL_FOR_ARCH8 | AARCH64_FL_CRC, cortexa53, "0x41", "0xd03")
-AARCH64_CORE("cortex-a57",  cortexa57, cortexa57, 8,  AARCH64_FL_FOR_ARCH8 | AARCH64_FL_CRC, cortexa57, "0x41", "0xd07")
+AARCH64_CORE("cortex-a57",  cortexa57, cortexa57, 8,  AARCH64_FL_FOR_ARCH8 | AARCH64_FL_CRC | AARCH64_FL_USE_FMA_STEERING_PASS, cortexa57, "0x41", "0xd07")
 AARCH64_CORE("cortex-a72",  cortexa72, cortexa57, 8,  AARCH64_FL_FOR_ARCH8 | AARCH64_FL_CRC, cortexa57, "0x41", "0xd08")
 AARCH64_CORE("exynos-m1",   exynosm1,  cortexa57, 8,  AARCH64_FL_FOR_ARCH8 | AARCH64_FL_CRC | AARCH64_FL_CRYPTO, cortexa57, "0x53", "0x001")
 AARCH64_CORE("thunderx",    thunderx,  thunderx,  8,  AARCH64_FL_FOR_ARCH8 | AARCH64_FL_CRC | AARCH64_FL_CRYPTO, thunderx,  "0x43", "0x0a1")
@@ -48,5 +48,5 @@ AARCH64_CORE("xgene1",      xgene1,    xgene1,    8,  AARCH64_FL_FOR_ARCH8, xgen
 
 /* V8 big.LITTLE implementations.  */
 
-AARCH64_CORE("cortex-a57.cortex-a53",  cortexa57cortexa53, cortexa53, 8,  AARCH64_FL_FOR_ARCH8 | AARCH64_FL_CRC, cortexa57, "0x41", "0xd07.0xd03")
+AARCH64_CORE("cortex-a57.cortex-a53",  cortexa57cortexa53, cortexa53, 8,  AARCH64_FL_FOR_ARCH8 | AARCH64_FL_CRC | AARCH64_FL_USE_FMA_STEERING_PASS, cortexa57, "0x41", "0xd07.0xd03")
 AARCH64_CORE("cortex-a72.cortex-a53",  cortexa72cortexa53, cortexa53, 8,  AARCH64_FL_FOR_ARCH8 | AARCH64_FL_CRC, cortexa57, "0x41", "0xd08.0xd03")
diff --git a/gcc/config/aarch64/aarch64.h b/gcc/config/aarch64/aarch64.h
index 1f7187b..3fd1b3f 100644
--- a/gcc/config/aarch64/aarch64.h
+++ b/gcc/config/aarch64/aarch64.h
@@ -200,6 +200,8 @@ extern unsigned aarch64_architecture_version;
 #define AARCH64_FL_CRYPTO     (1 << 2)	/* Has crypto.  */
 #define AARCH64_FL_SLOWMUL    (1 << 3)	/* A slow multiply core.  */
 #define AARCH64_FL_CRC        (1 << 4)	/* Has CRC.  */
+/* Has static dispatch of FMA.  */
+#define AARCH64_FL_USE_FMA_STEERING_PASS (1 << 5)
 
 /* Has FP and SIMD.  */
 #define AARCH64_FL_FPSIMD     (AARCH64_FL_FP | AARCH64_FL_SIMD)
@@ -220,6 +222,8 @@ extern unsigned long aarch64_isa_flags;
 /* Macros to test tuning flags.  */
 extern unsigned long aarch64_tune_flags;
 #define AARCH64_TUNE_SLOWMUL       (aarch64_tune_flags & AARCH64_FL_SLOWMUL)
+#define AARCH64_TUNE_FMA_STEERING \
+  (aarch64_tune_flags & AARCH64_FL_USE_FMA_STEERING_PASS)
 
 /* Crypto is an optional extension to AdvSIMD.  */
 #define TARGET_CRYPTO (TARGET_SIMD && AARCH64_ISA_CRYPTO)
diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
index dd92934..b8a91dc 100644
--- a/gcc/config/aarch64/aarch64.c
+++ b/gcc/config/aarch64/aarch64.c
@@ -95,6 +95,7 @@
 #include "rtl-iter.h"
 #include "tm-constrs.h"
 #include "sched-int.h"
+#include "cortex-a57-fma-steering.h"
 
 /* Defined for convenience.  */
 #define POINTER_BYTES (POINTER_SIZE / BITS_PER_UNIT)
@@ -6884,6 +6885,9 @@ aarch64_override_options (void)
 	align_functions = aarch64_tune_params->function_align;
     }
 
+  if (AARCH64_TUNE_FMA_STEERING)
+    aarch64_register_fma_steering ();
+
   aarch64_override_options_after_change ();
 }
 
diff --git a/gcc/config/aarch64/cortex-a57-fma-steering.h b/gcc/config/aarch64/cortex-a57-fma-steering.h
new file mode 100644
index 0000000..e8915ac
--- /dev/null
+++ b/gcc/config/aarch64/cortex-a57-fma-steering.h
@@ -0,0 +1,22 @@
+/* This file contains declarations for the FMA steering optimization
+   pass for Cortex-A57.
+   Copyright (C) 2015 Free Software Foundation, Inc.
+   Contributed by ARM Ltd.
+
+   This file is part of GCC.
+
+   GCC is free software; you can redistribute it and/or modify it
+   under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3, or (at your option)
+   any later version.
+
+   GCC is distributed in the hope that it will be useful, but
+   WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with GCC; see the file COPYING3.  If not see
+   <http://www.gnu.org/licenses/>.  */
+
+void aarch64_register_fma_steering (void);
diff --git a/gcc/config/aarch64/cortex-a57-fma-steering.c b/gcc/config/aarch64/cortex-a57-fma-steering.c
new file mode 100644
index 0000000..3d7557a
--- /dev/null
+++ b/gcc/config/aarch64/cortex-a57-fma-steering.c
@@ -0,0 +1,1088 @@
+/* FMA steering optimization pass for Cortex-A57.
+   Copyright (C) 2015 Free Software Foundation, Inc.
+   Contributed by ARM Ltd.
+
+   This file is part of GCC.
+
+   GCC is free software; you can redistribute it and/or modify it
+   under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3, or (at your option)
+   any later version.
+
+   GCC is distributed in the hope that it will be useful, but
+   WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with GCC; see the file COPYING3.  If not see
+   <http://www.gnu.org/licenses/>.  */
+
+#include "config.h"
+#include "system.h"
+#include "coretypes.h"
+#include "tm.h"
+#include "regs.h"
+#include "insn-config.h"
+#include "hard-reg-set.h"
+#include "dominance.h"
+#include "cfg.h"
+#include "cfganal.h"
+#include "predict.h"
+#include "basic-block.h"
+#include "insn-attr.h"
+#include "machmode.h"
+#include "recog.h"
+#include "output.h"
+#include "vec.h"
+#include "hash-map.h"
+#include "bitmap.h"
+#include "obstack.h"
+#include "df.h"
+#include "target.h"
+#include "rtl.h"
+#include "context.h"
+#include "tree-pass.h"
+#include "regrename.h"
+#include "cortex-a57-fma-steering.h"
+
+#include <list>
+
+/* For better performance, the destination of FMADD/FMSUB instructions should
+   have the same parity as their accumulator register if the accumulator
+   contains the result of a previous FMUL or FMADD/FMSUB instruction if
+   targetting Cortex-A57 processors.  Performance is also increased by
+   otherwise keeping a good balance in the parity of the destination register
+   of FMUL or FMADD/FMSUB.
+
+   This pass ensure that registers are renamed so that these conditions hold.
+   We reuse the existing register renaming facility from regrename.c to build
+   dependency chains and expose candidate registers for renaming.
+
+
+   The algorithm has three steps:
+
+   First, the functions of the register renaming pass are called.  These
+   analyze the instructions and produce a list of def/use chains of
+   instructions.
+
+   Next, this information is used to build trees of multiply and
+   multiply-accumulate instructions.  The roots of these trees are any
+   multiply, or any multiply-accumulate whose accumulator is not dependent on
+   a multiply or multiply-accumulate instruction.  A child is added to the
+   tree where a dependency chain exists between the result of the parent
+   instruction and the accumulator operand of the child, as in the diagram
+   below:
+
+		 fmul s2, s0, s1
+		/		\
+   fmadd s0, s1, s1, s2   fmadd s4, s1, s1 s2
+	    |
+   fmadd s3, s1, s1, s0
+
+   Trees made of a single instruction are permitted.
+
+   Finally, renaming is performed.  The parity of the destination register at
+   the root of a tree is checked against the current balance of multiply and
+   multiply-accumulate on each pipeline.  If necessary, the root of a tree is
+   renamed, in which case the rest of the tree is then renamed to keep the same
+   parity in the destination registers of all instructions in the tree.  */
+
+
+
+/* Forward declarations.  */
+class fma_node;
+class fma_root_node;
+class func_fma_steering;
+
+/* Dependencies between FMUL or FMADD/FMSUB instructions and subsequent
+   FMADD/FMSUB instructions form a graph.  This is because alternatives can
+   make a register be set by several FMUL or FMADD/FMSUB instructions in
+   different basic blocks and because of loops.  For ease of browsing, the
+   connected components of this graph are broken up into forests of trees.
+   Forests are represented by fma_forest objects, contained in the fma_forests
+   list.  Using a separate object for the forests allows for a better use of
+   memory as there is some information that is global to each forest, such as
+   the number of FMSUB and FMADD/FMSUB instructions currently scheduled on each
+   floating-point execution pipelines.  */
+
+class fma_forest
+{
+public:
+  fma_forest (func_fma_steering *, fma_root_node *, int);
+  ~fma_forest ();
+
+  int get_id ();
+  std::list<fma_root_node *> *get_roots ();
+  func_fma_steering *get_globals ();
+  int get_target_parity ();
+  void fma_node_created (fma_node *);
+  void merge_forest (fma_forest *);
+  void dump_info ();
+  void dispatch ();
+
+private:
+  /* The list of roots that form this forest.  */
+  std::list<fma_root_node *> *m_roots;
+
+  /* Target parity the destination register of all FMUL and FMADD/FMSUB
+     instructions in this forest should have.  */
+  int m_target_parity;
+
+  /* Link to the instance of func_fma_steering holding data related to the
+     FMA steering of the current function (cfun).  */
+  func_fma_steering *m_globals;
+
+  /* Identifier for the forest (used for dumps).  */
+  int m_id;
+
+  /* Total number of nodes in the forest (for statistics).  */
+  int m_nb_nodes;
+};
+
+class fma_node
+{
+public:
+  fma_node (fma_node *parent, du_chain *chain);
+  ~fma_node ();
+
+  bool root_p ();
+  fma_forest *get_forest ();
+  std::list<fma_node *> *get_children ();
+  rtx_insn *get_insn ();
+  void add_child (fma_node *);
+  int get_parity ();
+  void set_head (du_head *);
+  void rename (fma_forest *);
+  void dump_info (fma_forest *);
+
+protected:
+  /* Root node that lead to this node.  */
+  fma_root_node *m_root;
+
+  /* The parent node of this node.  If the node belong to a chain with several
+     parent nodes, the first one encountered in a depth-first search is chosen
+     as canonical parent.  */
+  fma_node *m_parent;
+
+  /* The list of child nodes.  If a chain contains several parent nodes, one is
+     chosen as canonical parent and the others will have no children.  */
+  std::list<fma_node *> *m_children;
+
+  /* The associated DU_HEAD chain that the insn represented by this object
+     is (one of) the root of.  When a chain contains several roots, the non
+     canonical ones have this field set to NULL.  */
+  struct du_head *m_head;
+
+  /* The FMUL or FMADD/FMSUB instruction this object corresponds to.  */
+  rtx_insn *m_insn;
+};
+
+class fma_root_node : public fma_node
+{
+public:
+  fma_root_node (func_fma_steering *, du_chain *, int);
+
+  fma_forest *get_forest ();
+  void set_forest (fma_forest *);
+  void dump_info (fma_forest *);
+
+private:
+  /* The forest this node belonged to when it was created.  */
+  fma_forest *m_forest;
+};
+
+/* Class holding all data and methods relative to the FMA steering of a given
+   function.  The FMA steering pass could then run in parallel for different
+   functions.  */
+
+class func_fma_steering
+{
+public:
+  func_fma_steering ();
+  ~func_fma_steering ();
+
+  int get_fpu_balance ();
+  void remove_forest (fma_forest *);
+  bool put_node (fma_node *);
+  void update_balance (int);
+  fma_node *get_fma_node (rtx_insn *);
+  void analyze_fma_fmul_insn (fma_forest *, du_chain *, du_head_p);
+  void execute_fma_steering ();
+
+private:
+  void dfs (void (*) (fma_forest *), void (*) (fma_forest *, fma_root_node *),
+	    void (*) (fma_forest *, fma_node *), bool);
+  void analyze ();
+  void rename_fma_trees ();
+
+  /* Mapping between FMUL or FMADD/FMSUB instructions and the associated
+     fma_node object.  Used when analyzing an instruction that is a root of
+     a chain to find if such an object was created because this instruction
+     is also a use in another chain.  */
+  hash_map<rtx_insn *, fma_node *> *m_insn_fma_head_map;
+
+  /* A list of all the forests in a given function.  */
+  std::list<fma_forest *> m_fma_forests;
+
+  /* Balance of FMUL and FMADD/FMSUB instructions between the two FPU
+     pipelines:
+     < 0: more instruction dispatched to the first pipeline
+     == 0: perfect balance
+     > 0: more instruction dispatched to the second pipeline.  */
+  int m_fpu_balance;
+
+  /* Identifier for the next forest created.  */
+  int m_next_forest_id;
+};
+
+/* Rename the register HEAD->regno in all the insns in the chain HEAD to any
+   register not in the set UNAVAILABLE.  Adapted from rename_chains in
+   regrename.c.  */
+
+static bool
+rename_single_chain (du_head_p head, HARD_REG_SET *unavailable)
+{
+  int best_new_reg;
+  int n_uses = 0;
+  struct du_chain *tmp;
+  int reg = head->regno;
+  enum reg_class super_class = NO_REGS;
+
+  if (head->cannot_rename)
+    return false;
+
+  if (fixed_regs[reg] || global_regs[reg]
+      || (frame_pointer_needed && reg == HARD_FRAME_POINTER_REGNUM))
+    return false;
+
+  /* Iterate over elements in the chain in order to:
+     1. Count number of uses, and narrow the set of registers we can
+	use for renaming.
+     2. Compute the superunion of register classes in this chain.  */
+  for (tmp = head->first; tmp; tmp = tmp->next_use)
+    {
+      if (DEBUG_INSN_P (tmp->insn))
+	continue;
+      n_uses++;
+      IOR_COMPL_HARD_REG_SET (*unavailable, reg_class_contents[tmp->cl]);
+      super_class = reg_class_superunion[(int) super_class][(int) tmp->cl];
+    }
+
+  if (n_uses < 1)
+    return false;
+
+  best_new_reg = find_rename_reg (head, super_class, unavailable, reg,
+				  false);
+
+  if (dump_file)
+    {
+      fprintf (dump_file, "Register %s in insn %d", reg_names[reg],
+	       INSN_UID (head->first->insn));
+      if (head->need_caller_save_reg)
+	fprintf (dump_file, " crosses a call");
+    }
+
+  if (best_new_reg == reg)
+    {
+      if (dump_file)
+	fprintf (dump_file, "; no available better choice\n");
+      return false;
+    }
+
+  if (dump_file)
+    fprintf (dump_file, ", renamed as %s\n", reg_names[best_new_reg]);
+
+  regrename_do_replace (head, best_new_reg);
+  df_set_regs_ever_live (best_new_reg, true);
+  return true;
+}
+
+/* Return whether T is the attribute of a FMADD/FMSUB-like instruction.  */
+
+static bool
+is_fmac_op (enum attr_type t)
+{
+  return (t == TYPE_FMACS) || (t == TYPE_FMACD) || (t == TYPE_NEON_FP_MLA_S);
+}
+
+/* Return whether T is the attribute of a FMUL instruction.  */
+
+static bool
+is_fmul_op (enum attr_type t)
+{
+  return (t == TYPE_FMULS) || (t == TYPE_FMULD) || (t == TYPE_NEON_FP_MUL_S);
+}
+
+/* Return whether INSN is an FMUL (if FMUL_OK is true) or FMADD/FMSUB
+   instruction.  */
+
+static bool
+is_fmul_fmac_insn (rtx_insn *insn, bool fmul_ok)
+{
+  enum attr_type t;
+
+  if (!NONDEBUG_INSN_P (insn))
+    return false;
+
+  if (recog_memoized (insn) < 0)
+    return false;
+
+  /* Only consider chain(s) this instruction is a root of if this is an FMUL or
+     FMADD/FMSUB instruction.  This allows to avoid browsing chains of all
+     instructions for FMUL or FMADD/FMSUB in them.  */
+  t = get_attr_type (insn);
+  return is_fmac_op (t) || (fmul_ok && is_fmul_op (t));
+}
+
+
+/*
+ * Class fma_forest method definitions.
+ */
+
+fma_forest::fma_forest (func_fma_steering *fma_steer, fma_root_node *fma_root,
+			int id)
+{
+      memset (this, 0, sizeof (*this));
+      this->m_globals = fma_steer;
+      this->m_roots = new std::list<fma_root_node *>;
+      this->m_roots->push_back (fma_root);
+      this->m_id = id;
+}
+
+fma_forest::~fma_forest ()
+{
+  delete this->m_roots;
+}
+
+int
+fma_forest::get_id ()
+{
+  return this->m_id;
+}
+
+std::list<fma_root_node *> *
+fma_forest::get_roots ()
+{
+  return this->m_roots;
+}
+
+func_fma_steering *
+fma_forest::get_globals ()
+{
+  return this->m_globals;
+}
+
+int
+fma_forest::get_target_parity ()
+{
+  return this->m_target_parity;
+}
+
+/* Act on the creation of NODE by updating statistics in FOREST and adding an
+   entry for it in the func_fma_steering hashmap.  */
+
+void fma_forest::fma_node_created (fma_node *node)
+{
+  bool created = !this->m_globals->put_node (node);
+
+  gcc_assert (created);
+  this->m_nb_nodes++;
+}
+
+/* Merge REF_FOREST and OTHER_FOREST together, making REF_FOREST the canonical
+   fma_forest object to represent both.  */
+
+void
+fma_forest::merge_forest (fma_forest *other_forest)
+{
+  std::list<fma_root_node *> *other_roots;
+  std::list<fma_root_node *>::iterator other_root_iter;
+
+  if (this == other_forest)
+    return;
+
+  other_roots = other_forest->m_roots;
+
+  /* Update root nodes' pointer to forest.  */
+  for (other_root_iter = other_roots->begin ();
+       other_root_iter != other_roots->end (); other_root_iter++)
+    (*other_root_iter)->set_forest (this);
+
+  /* Remove other_forest from the list of forests and move its tree roots in
+     the list of tree roots of ref_forest.  */
+  this->m_globals->remove_forest (other_forest);
+  this->m_roots->splice (this->m_roots->begin (), *other_roots);
+  delete other_forest;
+
+  this->m_nb_nodes += other_forest->m_nb_nodes;
+}
+
+/* Dump information about the forest FOREST.  */
+
+void
+fma_forest::dump_info ()
+{
+  gcc_assert (dump_file);
+
+  fprintf (dump_file, "Forest #%d has %d nodes\n", this->m_id,
+	   this->m_nb_nodes);
+}
+
+/* Wrapper around fma_forest::dump_info for use as parameter of function
+   pointer type in func_fma_steering::dfs.  */
+
+static void
+dump_forest_info (fma_forest *forest)
+{
+  forest->dump_info ();
+}
+
+/* Dispatch forest to the least utilized pipeline.  */
+
+void
+fma_forest::dispatch ()
+{
+  this->m_target_parity = this->m_roots->front ()->get_parity ();
+  int fpu_balance = this->m_globals->get_fpu_balance ();
+  if (fpu_balance != 0)
+    this->m_target_parity = (fpu_balance < 0);
+
+  if (dump_file)
+    fprintf (dump_file, "Target parity for forest #%d: %s\n", this->m_id,
+	     this->m_target_parity ? "odd" : "even");
+}
+
+/* Wrapper around fma_forest::dispatch for use as parameter of function pointer
+   type in func_fma_steering::dfs.  */
+
+static void
+dispatch_forest (fma_forest *forest)
+{
+  forest->dispatch ();
+}
+
+fma_node::fma_node (fma_node *parent, du_chain *chain)
+{
+  memset (this, 0, sizeof (*this));
+  this->m_parent = parent;
+  this->m_children = new std::list<fma_node *>;
+  this->m_insn = chain->insn;
+  /* root_p () cannot be used to check for root before root is set.  */
+  if (this->m_parent == this)
+    this->m_root = static_cast<fma_root_node *> (parent);
+  else
+    {
+      this->m_root = parent->m_root;
+      this->get_forest ()->fma_node_created (this);
+    }
+}
+
+fma_node::~fma_node ()
+{
+  delete this->m_children;
+}
+
+std::list<fma_node *> *
+fma_node::get_children ()
+{
+  return this->m_children;
+}
+
+rtx_insn *
+fma_node::get_insn ()
+{
+  return this->m_insn;
+}
+
+void
+fma_node::set_head (du_head *head)
+{
+  gcc_assert (!this->m_head);
+  this->m_head = head;
+}
+
+/* Add a child to this node in the list of children.  */
+
+void
+fma_node::add_child (fma_node *child)
+{
+  this->m_children->push_back (child);
+}
+
+/* Return the parity of the destination register of the instruction represented
+   by this node.  */
+
+int
+fma_node::get_parity ()
+{
+  return this->m_head->regno % 2;
+}
+
+/* Get the actual forest associated with a non root node as the one the node
+   points to might have been merged into another one.  In that case the pointer
+   in the root nodes are updated so we return the forest pointer of a root node
+   pointed to by the initial forest.  Despite being a oneliner, this method is
+   defined here as it references a method from fma_root_node.  */
+
+fma_forest *
+fma_node::get_forest ()
+{
+  return this->m_root->get_forest ();
+}
+
+/* Return whether a node is a root node.  */
+
+bool
+fma_node::root_p ()
+{
+  return this->m_root == this;
+}
+
+/* Dump information about the children of node FMA_NODE in forest FOREST.  */
+
+void
+fma_node::dump_info (ATTRIBUTE_UNUSED fma_forest *forest)
+{
+  struct du_chain *chain;
+  std::list<fma_node *>::iterator fma_child;
+
+  gcc_assert (dump_file);
+
+  if (this->get_children ()->empty ())
+    return;
+
+  fprintf (dump_file, "Instruction(s)");
+  for (chain = this->m_head->first; chain; chain = chain->next_use)
+    {
+      if (!is_fmul_fmac_insn (chain->insn, true))
+	continue;
+
+      if (chain->loc != &SET_DEST (PATTERN (chain->insn)))
+	continue;
+
+      fprintf (dump_file, " %d", INSN_UID (chain->insn));
+    }
+
+  fprintf (dump_file, " is(are) accumulator dependency of instructions");
+  for (fma_child = this->get_children ()->begin ();
+       fma_child != this->get_children ()->end (); fma_child++)
+    fprintf (dump_file, " %d", INSN_UID ((*fma_child)->m_insn));
+  fprintf (dump_file, "\n");
+}
+
+/* Wrapper around fma_node::dump_info for use as parameter of function pointer
+   type in func_fma_steering::dfs.  */
+
+static void
+dump_tree_node_info (fma_forest *forest, fma_node *node)
+{
+  node->dump_info (forest);
+}
+
+/* Rename the destination register of a single FMUL or FMADD/FMSUB instruction
+   represented by FMA_NODE to a register that respect the target parity for
+   FOREST or with same parity of the instruction represented by its parent node
+   if it has one.  */
+
+void
+fma_node::rename (fma_forest *forest)
+{
+  int cur_parity, target_parity;
+
+  /* This is alternate root of a chain and thus has no children.  It will be
+     renamed when processing the canonical root for that chain.  */
+  if (!this->m_head)
+    return;
+
+  target_parity = forest->get_target_parity ();
+  if (this->m_parent)
+    target_parity = this->m_parent->get_parity ();
+  cur_parity = this->get_parity ();
+
+  /* Rename if parity differs.  */
+  if (cur_parity != target_parity)
+    {
+      rtx_insn *insn = this->m_insn;
+      HARD_REG_SET unavailable;
+      enum machine_mode mode;
+      int reg;
+
+      if (dump_file)
+	{
+	  unsigned cur_dest_reg = this->m_head->regno;
+
+	  fprintf (dump_file, "FMA or FMUL at insn %d but destination "
+		   "register (%s) has different parity from expected to "
+		   "maximize FPU pipeline utilization\n", INSN_UID (insn),
+		   reg_names[cur_dest_reg]);
+	}
+
+      /* Don't clobber traceback for noreturn functions.  */
+      CLEAR_HARD_REG_SET (unavailable);
+      if (frame_pointer_needed)
+	{
+	  add_to_hard_reg_set (&unavailable, Pmode, FRAME_POINTER_REGNUM);
+	  add_to_hard_reg_set (&unavailable, Pmode, HARD_FRAME_POINTER_REGNUM);
+	}
+
+      /* Exclude registers with wrong parity.  */
+      mode = GET_MODE (SET_DEST (PATTERN (insn)));
+      for (reg = cur_parity; reg < FIRST_PSEUDO_REGISTER; reg += 2)
+	add_to_hard_reg_set (&unavailable, mode, reg);
+
+      if (!rename_single_chain (this->m_head, &unavailable))
+	{
+	  if (dump_file)
+	    fprintf (dump_file, "Destination register of insn %d could not be "
+		     "renamed. Dependent FMA insns will use this parity from "
+		     "there on.\n", INSN_UID (insn));
+	}
+      else
+	cur_parity = target_parity;
+    }
+
+  forest->get_globals ()->update_balance (cur_parity);
+}
+
+/* Wrapper around fma_node::dump_info for use as parameter of function pointer
+   type in func_fma_steering::dfs.  */
+
+static void
+rename_fma_node (fma_forest *forest, fma_node *node)
+{
+  node->rename (forest);
+}
+
+fma_root_node::fma_root_node (func_fma_steering *globals, du_chain *chain,
+			      int id) : fma_node (this, chain)
+{
+  this->m_forest = new fma_forest (globals, this, id);
+  this->m_forest->fma_node_created (this);
+}
+
+fma_forest *
+fma_root_node::get_forest ()
+{
+  return this->m_forest;
+}
+
+void
+fma_root_node::set_forest (fma_forest *ref_forest)
+{
+  this->m_forest = ref_forest;
+}
+
+/* Dump information about the roots of forest FOREST.  */
+
+void
+fma_root_node::dump_info (fma_forest *forest)
+{
+  gcc_assert (dump_file);
+
+  if (this == forest->get_roots ()->front ())
+    fprintf (dump_file, "Instruction(s) at root of forest #%d:",
+	     forest->get_id ());
+  fprintf (dump_file, " %d", INSN_UID (this->m_insn));
+  if (this == forest->get_roots ()->back ())
+    fprintf (dump_file, "\n");
+}
+
+/* Wrapper around fma_root_node::dump_info for use as parameter of function
+   pointer type in func_fma_steering::dfs.  */
+
+static void
+dump_tree_root_info (fma_forest *forest, fma_root_node *node)
+{
+  node->dump_info (forest);
+}
+
+func_fma_steering::func_fma_steering () : m_fpu_balance (0)
+{
+  this->m_insn_fma_head_map = new hash_map<rtx_insn *, fma_node *>;
+  this->m_fma_forests.clear ();
+  this->m_next_forest_id = 0;
+}
+
+func_fma_steering::~func_fma_steering ()
+{
+  delete this->m_insn_fma_head_map;
+}
+
+int
+func_fma_steering::get_fpu_balance ()
+{
+  return this->m_fpu_balance;
+}
+
+void
+func_fma_steering::remove_forest (fma_forest *forest)
+{
+  this->m_fma_forests.remove (forest);
+}
+
+/* Memorize the mapping of this instruction to its fma_node object and return
+   whether such a mapping existed.  */
+
+bool
+func_fma_steering::put_node (fma_node *node)
+{
+  return this->m_insn_fma_head_map->put (node->get_insn (), node);
+}
+
+/* Update the current balance considering a node with the given PARITY.  */
+
+void
+func_fma_steering::update_balance (int parity)
+{
+  this->m_fpu_balance = parity ? this->m_fpu_balance + 1
+			       : this->m_fpu_balance - 1;
+}
+
+/* Return whether an fma_node object exists for instruction INSN and, if not,
+   allocate one in *RET.  */
+
+fma_node *
+func_fma_steering::get_fma_node (rtx_insn *insn)
+{
+  fma_node **fma_slot;
+
+  fma_slot = this->m_insn_fma_head_map->get (insn);
+  if (fma_slot)
+    return *fma_slot;
+  return NULL;
+}
+
+/* Allocate and initialize fma_node objects for the FMUL or FMADD/FMSUB
+   instruction in CHAIN->insn and its dependent FMADD/FMSUB instructions, all
+   part of FOREST.  For the children, the associated head is left untouched
+   (and thus null) as this function will be called again when considering the
+   chain where they are def.  For the parent, the chain is given in HEAD.  */
+
+void
+func_fma_steering::analyze_fma_fmul_insn (fma_forest *ref_forest,
+					  du_chain *chain, du_head_p head)
+{
+  fma_forest *forest;
+  fma_node *node = this->get_fma_node (chain->insn);
+
+  /* This is a root node.  */
+  if (!node)
+    {
+      fma_root_node *root_node;
+
+      root_node = new fma_root_node (this, chain, this->m_next_forest_id++);
+      forest = root_node->get_forest ();
+      node = root_node;
+
+      /* Until proved otherwise, assume this root is not part of an existing
+	 forest and thus add its forest to the list of forests.  */
+      this->m_fma_forests.push_back (forest);
+    }
+  else
+    forest = node->get_forest ();
+
+  node->set_head (head);
+
+  /* fma_node is part of a chain with several defs, one of them having already
+     been processed.  The root of that already processed def is the canonical
+     one and the root of fma_node is added to its forest.  No need to process
+     the children nodes as they were already processed when the other def was
+     processed.  */
+  if (ref_forest)
+    {
+      ref_forest->merge_forest (forest);
+      return;
+    }
+
+  for (chain = head->first; chain; chain = chain->next_use)
+    {
+      fma_node *child_fma;
+      rtx fma_rtx, *accum_rtx_p;
+
+      if (!is_fmul_fmac_insn (chain->insn, false))
+	continue;
+
+      /* Get FMA rtx.  */
+      fma_rtx = SET_SRC (PATTERN (chain->insn));
+      /* FMA is negated.  */
+      if (GET_CODE (fma_rtx) == NEG)
+	fma_rtx = XEXP (fma_rtx, 0);
+      /* Get accumulator rtx.  */
+      accum_rtx_p = &XEXP (fma_rtx, 2);
+      /* Accumulator is negated.  */
+      if (!REG_P (*accum_rtx_p))
+	accum_rtx_p = &XEXP (*accum_rtx_p, 0);
+
+      /* This du_chain structure is not for the accumulator register.  */
+      if (accum_rtx_p != chain->loc)
+	continue;
+
+      /* If object already created, this is a loop carried dependency.  We
+	 don't include this object in the children as we want trees for
+	 rename_fma_trees to not be an infinite loop.  */
+      if (this->get_fma_node (chain->insn))
+	continue;
+
+      child_fma = new fma_node (node, chain);
+
+      /* Memorize the mapping of this instruction to its fma_node object
+	 as it will be processed for the chain starting at its destination
+	 register later.  */
+
+      /* Link to siblings.  */
+      node->add_child (child_fma);
+    }
+}
+
+/* Perform a depth-first search of the forests of fma_node in
+   THIS->m_fma_forests, calling PROCESS_FOREST () on each fma_forest object in
+   THIS->m_fma_forests list, PROCESS_ROOT () on each tree root and
+   PROCESS_NODE () on each node.  If FREE is true, free all std::list in the
+   same dfs.  */
+
+void
+func_fma_steering::dfs (void (*process_forest) (fma_forest *),
+			void (*process_root) (fma_forest *, fma_root_node *),
+			void (*process_node) (fma_forest *, fma_node *),
+			bool free)
+{
+  vec<fma_node *> to_process;
+  std::list<fma_forest *>::iterator forest_iter;
+
+  to_process.create (0);
+
+  /* For each forest.  */
+  for (forest_iter = this->m_fma_forests.begin ();
+       forest_iter != this->m_fma_forests.end (); forest_iter++)
+    {
+      std::list<fma_root_node *>::iterator root_iter;
+
+      if (process_forest)
+	process_forest (*forest_iter);
+
+      /* For each tree root in this forest.  */
+      for (root_iter = (*forest_iter)->get_roots ()->begin ();
+	   root_iter != (*forest_iter)->get_roots ()->end (); root_iter++)
+	{
+	  if (process_root)
+	    process_root (*forest_iter, *root_iter);
+	  to_process.safe_push (*root_iter);
+	}
+
+      /* For each tree node in this forest.  */
+      while (!to_process.is_empty ())
+	{
+	  fma_node *node;
+	  std::list<fma_node *>::iterator child_iter;
+
+	  node = to_process.pop ();
+
+	  if (process_node)
+	    process_node (*forest_iter, node);
+
+	  /* Absence of children might indicate an alternate root of a *chain*.
+	     It's ok to skip it here as the chain will be renamed when
+	     processing the canonical root for that chain.  */
+	  if (node->get_children ()->empty ())
+	    continue;
+
+	  for (child_iter = node->get_children ()->begin ();
+	       child_iter != node->get_children ()->end (); child_iter++)
+	    to_process.safe_push (*child_iter);
+	  if (free)
+	    {
+	      if (node->root_p ())
+		delete static_cast<fma_root_node *> (node);
+	      else
+		delete node;
+	    }
+	}
+      if (free)
+	delete *forest_iter;
+    }
+
+  to_process.release ();
+}
+
+/* Build the dependency trees of FMUL and FMADD/FMSUB instructions.  */
+
+void
+func_fma_steering::analyze ()
+{
+  int i, n_blocks, *bb_dfs_preorder;
+  basic_block bb;
+  rtx_insn *insn;
+
+  bb_dfs_preorder = XNEWVEC (int, last_basic_block_for_fn (cfun));
+  n_blocks = pre_and_rev_post_order_compute (bb_dfs_preorder, NULL, false);
+
+  /* Browse the graph of basic blocks looking for FMUL or FMADD/FMSUB
+     instructions.  */
+  for (i = 0; i < n_blocks; i++)
+    {
+      bb = BASIC_BLOCK_FOR_FN (cfun, bb_dfs_preorder[i]);
+      FOR_BB_INSNS (bb, insn)
+	{
+	  operand_rr_info *dest_op_info;
+	  struct du_chain *chain;
+	  unsigned dest_regno;
+	  fma_forest *forest;
+	  du_head_p head;
+	  int i;
+
+	  if (!is_fmul_fmac_insn (insn, true))
+	    continue;
+
+	  /* Search the chain where this instruction is (one of) the root.  */
+	  dest_op_info = insn_rr[INSN_UID (insn)].op_info;
+	  dest_regno = REGNO (SET_DEST (PATTERN (insn)));
+	  for (i = 0; i < dest_op_info->n_chains; i++)
+	    {
+	      /* The register tracked by this chain does not match the
+		 destination register of insn.  */
+	      if (dest_op_info->heads[i]->regno != dest_regno)
+		continue;
+
+	      head = dest_op_info->heads[i];
+	      /* The chain was merged in another, find the new head.  */
+	      if (!head->first)
+		head = regrename_chain_from_id (head->id);
+
+	      /* Search the chain element for this instruction and, if another
+		 FMUL or FMADD/FMSUB instruction was already processed, note
+		 the forest of its tree.  */
+	      forest = NULL;
+	      for (chain = head->first; chain; chain = chain->next_use)
+		{
+		  fma_node **fma_slot;
+
+		  if (!is_fmul_fmac_insn (chain->insn, true))
+		    continue;
+
+		  /* This is a use, continue.  */
+		  if (chain->loc != &SET_DEST (PATTERN (chain->insn)))
+		    continue;
+
+		  if (chain->insn == insn)
+		    break;
+
+		  fma_slot = this->m_insn_fma_head_map->get (chain->insn);
+		  if (fma_slot && (*fma_slot)->get_children ())
+		    forest = (*fma_slot)->get_forest ();
+		}
+	      if (chain)
+		break;
+	    }
+
+	  /* We didn't find a chain with a def for this instruction.  */
+	  gcc_assert (i < dest_op_info->n_chains);
+
+	  this->analyze_fma_fmul_insn (forest, chain, head);
+	}
+    }
+  free (bb_dfs_preorder);
+
+  if (dump_file)
+    this->dfs (dump_forest_info, dump_tree_root_info, dump_tree_node_info,
+	       false);
+}
+
+/* Perform the renaming of all chains with FMUL or FMADD/FMSUB involved with
+   the objective of keeping FPU pipeline balanced in term of instructions and
+   having FMADD/FMSUB with dependencies on previous FMUL or FMADD/FMSUB be
+   scheduled on the same pipeline.  */
+
+void
+func_fma_steering::rename_fma_trees ()
+{
+  this->dfs (dispatch_forest, NULL, rename_fma_node, true);
+
+  if (dump_file && !this->m_fma_forests.empty ())
+    {
+      fprintf (dump_file, "Function %s has ", current_function_name ());
+      if (this->m_fpu_balance == 0)
+	fprintf (dump_file, "perfect balance of FMUL/FMA chains between the "
+		 "two FPU pipelines\n");
+      else if (this->m_fpu_balance > 0)
+	fprintf (dump_file, "%d more FMUL/FMA chains scheduled on the second "
+		 "FPU pipeline\n", this->m_fpu_balance);
+      else /* this->m_fpu_balance < 0 */
+	fprintf (dump_file, "%d more FMUL/FMA chains scheduled on the first "
+		 "FPU pipeline\n", - this->m_fpu_balance);
+    }
+}
+
+/* Execute FMA steering pass.  */
+
+void
+func_fma_steering::execute_fma_steering ()
+{
+  df_set_flags (DF_LR_RUN_DCE);
+  df_note_add_problem ();
+  df_analyze ();
+  df_set_flags (DF_DEFER_INSN_RESCAN);
+
+  regrename_init (true);
+  regrename_analyze (NULL);
+  this->analyze ();
+  this->rename_fma_trees ();
+  regrename_finish ();
+}
+
+const pass_data pass_data_fma_steering =
+{
+  RTL_PASS, /* type */
+  "fma_steering", /* name */
+  OPTGROUP_NONE, /* optinfo_flags */
+  TV_NONE, /* tv_id */
+  0, /* properties_required */
+  0, /* properties_provided */
+  0, /* properties_destroyed */
+  0, /* todo_flags_start */
+  TODO_df_finish, /* todo_flags_finish */
+};
+
+class pass_fma_steering : public rtl_opt_pass
+{
+public:
+  pass_fma_steering (gcc::context *ctxt)
+    : rtl_opt_pass (pass_data_fma_steering, ctxt)
+  {}
+
+  /* opt_pass methods: */
+  virtual bool gate (function *)
+    {
+      return optimize >= 2;
+    }
+
+  virtual unsigned int execute (function *)
+    {
+      func_fma_steering *fma_steering = new func_fma_steering;
+      fma_steering->execute_fma_steering ();
+      delete fma_steering;
+      return 0;
+    }
+
+}; // class pass_fma_steering
+
+/* Create a new fma steering pass instance.  */
+
+static rtl_opt_pass *
+make_pass_fma_steering (gcc::context *ctxt)
+{
+  return new pass_fma_steering (ctxt);
+}
+
+/* Register the FMA steering pass to the pass manager.  */
+
+void
+aarch64_register_fma_steering ()
+{
+  opt_pass *pass_fma_steering = make_pass_fma_steering (g);
+
+  static struct register_pass_info fma_steering_info
+    = { pass_fma_steering, "rnreg", 1, PASS_POS_INSERT_AFTER };
+
+  register_pass (&fma_steering_info);
+}
diff --git a/gcc/config/aarch64/t-aarch64 b/gcc/config/aarch64/t-aarch64
index e410bc9..0371203 100644
--- a/gcc/config/aarch64/t-aarch64
+++ b/gcc/config/aarch64/t-aarch64
@@ -48,6 +48,15 @@ aarch-common.o: $(srcdir)/config/arm/aarch-common.c $(CONFIG_H) $(SYSTEM_H) \
 	$(COMPILER) -c $(ALL_COMPILERFLAGS) $(ALL_CPPFLAGS) $(INCLUDES) \
 		$(srcdir)/config/arm/aarch-common.c
 
+cortex-a57-fma-steering.o: $(srcdir)/config/aarch64/cortex-a57-fma-steering.c \
+    $(CONFIG_H) $(SYSTEM_H) $(TM_H) $(REGS_H) insn-config.h $(RTL_BASE_H) \
+    dominance.h cfg.h cfganal.h $(BASIC_BLOCK_H) $(INSN_ATTR_H) $(RECOG_H) \
+    output.h hash-map.h $(DF_H) $(OBSTACK_H) $(TARGET_H) $(RTL_H) \
+    $(CONTEXT_H) $(TREE_PASS_H) regrename.h \
+    $(srcdir)/config/aarch64/cortex-a57-fma-steering.h
+	$(COMPILER) -c $(ALL_COMPILERFLAGS) $(ALL_CPPFLAGS) $(INCLUDES) \
+		$(srcdir)/config/aarch64/cortex-a57-fma-steering.c
+
 comma=,
 MULTILIB_OPTIONS    = $(subst $(comma),/, $(patsubst %, mabi=%, $(subst $(comma),$(comma)mabi=,$(TM_MULTILIB_CONFIG))))
 MULTILIB_DIRNAMES   = $(subst $(comma), ,$(TM_MULTILIB_CONFIG))


Best regards,

Thomas