tree-pass.h (pass_strength_reduction): New decl.

gcc:

2012-06-26  Bill Schmidt  <wschmidt@linux.ibm.com>

	* tree-pass.h (pass_strength_reduction): New decl.
	* tree-ssa-loop-ivopts.c (initialize_costs): Make non-static.
	(finalize_costs): Likewise.
	* timevar.def (TV_TREE_SLSR): New timevar.
	* gimple-ssa-strength-reduction.c: New.
	* tree-flow.h (initialize_costs): New decl.
	(finalize_costs): Likewise.
	* Makefile.in (tree-ssa-strength-reduction.o): New dependencies.
	* passes.c (init_optimization_passes): Add pass_strength_reduction.

gcc/testsuite:

2012-06-26  Bill Schmidt  <wschmidt@linux.ibm.com>

	* gcc.dg/tree-ssa/slsr-1.c: New test.
	* gcc.dg/tree-ssa/slsr-2.c: Likewise.
	* gcc.dg/tree-ssa/slsr-3.c: Likewise.
	* gcc.dg/tree-ssa/slsr-4.c: Likewise.

From-SVN: r188989

1 files changed, 1526 insertions, 0 deletions

diff --git a/gcc/gimple-ssa-strength-reduction.c b/gcc/gimple-ssa-strength-reduction.c
new file mode 100644
index 0000000..f68562a
--- /dev/null
+++ b/gcc/gimple-ssa-strength-reduction.c
@@ -0,0 +1,1526 @@
+/* Straight-line strength reduction.
+   Copyright (C) 2012  Free Software Foundation, Inc.
+   Contributed by Bill Schmidt, IBM <wschmidt@linux.ibm.com>
+
+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/>.  */
+
+/* There are many algorithms for performing strength reduction on
+   loops.  This is not one of them.  IVOPTS handles strength reduction
+   of induction variables just fine.  This pass is intended to pick
+   up the crumbs it leaves behind, by considering opportunities for
+   strength reduction along dominator paths.
+
+   Strength reduction will be implemented in four stages, gradually
+   adding more complex candidates:
+
+   1) Explicit multiplies, known constant multipliers, no
+      conditional increments. (complete)
+   2) Explicit multiplies, unknown constant multipliers,
+      no conditional increments. (data gathering complete,
+      replacements pending)
+   3) Implicit multiplies in addressing expressions. (pending)
+   4) Explicit multiplies, conditional increments. (pending)
+
+   It would also be possible to apply strength reduction to divisions
+   and modulos, but such opportunities are relatively uncommon.
+
+   Strength reduction is also currently restricted to integer operations.
+   If desired, it could be extended to floating-point operations under
+   control of something like -funsafe-math-optimizations.  */
+
+#include "config.h"
+#include "system.h"
+#include "coretypes.h"
+#include "tree.h"
+#include "gimple.h"
+#include "basic-block.h"
+#include "tree-pass.h"
+#include "timevar.h"
+#include "cfgloop.h"
+#include "tree-pretty-print.h"
+#include "gimple-pretty-print.h"
+#include "tree-flow.h"
+#include "domwalk.h"
+#include "pointer-set.h"
+
+/* Information about a strength reduction candidate.  Each statement
+   in the candidate table represents an expression of one of the
+   following forms (the special case of CAND_REF will be described
+   later):
+
+   (CAND_MULT)  S1:  X = (B + i) * S
+   (CAND_ADD)   S1:  X = B + (i * S)
+
+   Here X and B are SSA names, i is an integer constant, and S is
+   either an SSA name or a constant.  We call B the "base," i the
+   "index", and S the "stride."
+
+   Any statement S0 that dominates S1 and is of the form:
+
+   (CAND_MULT)  S0:  Y = (B + i') * S
+   (CAND_ADD)   S0:  Y = B + (i' * S)
+
+   is called a "basis" for S1.  In both cases, S1 may be replaced by
+   
+                S1':  X = Y + (i - i') * S,
+
+   where (i - i') * S is folded to the extent possible.
+
+   All gimple statements are visited in dominator order, and each
+   statement that may contribute to one of the forms of S1 above is
+   given at least one entry in the candidate table.  Such statements
+   include addition, pointer addition, subtraction, multiplication,
+   negation, copies, and nontrivial type casts.  If a statement may
+   represent more than one expression of the forms of S1 above, 
+   multiple "interpretations" are stored in the table and chained
+   together.  Examples:
+
+   * An add of two SSA names may treat either operand as the base.
+   * A multiply of two SSA names, likewise.
+   * A copy or cast may be thought of as either a CAND_MULT with
+     i = 0 and S = 1, or as a CAND_ADD with i = 0 or S = 0.
+
+   Candidate records are allocated from an obstack.  They are addressed
+   both from a hash table keyed on S1, and from a vector of candidate
+   pointers arranged in predominator order.
+
+   Opportunity note
+   ----------------
+   Currently we don't recognize:
+
+     S0: Y = (S * i') - B
+     S1: X = (S * i) - B
+
+   as a strength reduction opportunity, even though this S1 would
+   also be replaceable by the S1' above.  This can be added if it
+   comes up in practice.  */
+
+
+/* Index into the candidate vector, offset by 1.  VECs are zero-based,
+   while cand_idx's are one-based, with zero indicating null.  */
+typedef unsigned cand_idx;
+
+/* The kind of candidate.  */
+enum cand_kind
+{
+  CAND_MULT,
+  CAND_ADD
+};
+
+struct slsr_cand_d
+{
+  /* The candidate statement S1.  */
+  gimple cand_stmt;
+
+  /* The base SSA name B.  */
+  tree base_name;
+
+  /* The stride S.  */
+  tree stride;
+
+  /* The index constant i.  */
+  double_int index;
+
+  /* The type of the candidate.  This is normally the type of base_name,
+     but casts may have occurred when combining feeding instructions.
+     A candidate can only be a basis for candidates of the same final type.  */
+  tree cand_type;
+
+  /* The kind of candidate (CAND_MULT, etc.).  */
+  enum cand_kind kind;
+
+  /* Index of this candidate in the candidate vector.  */
+  cand_idx cand_num;
+
+  /* Index of the next candidate record for the same statement.
+     A statement may be useful in more than one way (e.g., due to
+     commutativity).  So we can have multiple "interpretations"
+     of a statement.  */
+  cand_idx next_interp;
+
+  /* Index of the basis statement S0, if any, in the candidate vector.  */
+  cand_idx basis;
+
+  /* First candidate for which this candidate is a basis, if one exists.  */
+  cand_idx dependent;
+
+  /* Next candidate having the same basis as this one.  */
+  cand_idx sibling;
+
+  /* If this is a conditional candidate, the defining PHI statement
+     for the base SSA name B.  For future use; always NULL for now.  */
+  gimple def_phi;
+
+  /* Savings that can be expected from eliminating dead code if this
+     candidate is replaced.  */
+  int dead_savings;
+};
+
+typedef struct slsr_cand_d slsr_cand, *slsr_cand_t;
+typedef const struct slsr_cand_d *const_slsr_cand_t;
+
+/* Pointers to candidates are chained together as part of a mapping
+   from SSA names to the candidates that use them as a base name.  */
+
+struct cand_chain_d
+{
+  /* SSA name that serves as a base name for the chain of candidates.  */
+  tree base_name;
+
+  /* Pointer to a candidate.  */
+  slsr_cand_t cand;
+
+  /* Chain pointer.  */
+  struct cand_chain_d *next;
+
+};
+
+typedef struct cand_chain_d cand_chain, *cand_chain_t;
+typedef const struct cand_chain_d *const_cand_chain_t;
+
+/* Candidates are maintained in a vector.  If candidate X dominates
+   candidate Y, then X appears before Y in the vector; but the
+   converse does not necessarily hold.  */
+DEF_VEC_P (slsr_cand_t);
+DEF_VEC_ALLOC_P (slsr_cand_t, heap);
+static VEC (slsr_cand_t, heap) *cand_vec;
+
+enum cost_consts
+{
+  COST_NEUTRAL = 0,
+  COST_INFINITE = 1000
+};
+
+/* Pointer map embodying a mapping from statements to candidates.  */
+static struct pointer_map_t *stmt_cand_map;
+
+/* Obstack for candidates.  */
+static struct obstack cand_obstack;
+
+/* Array mapping from base SSA names to chains of candidates.  */
+static cand_chain_t *base_cand_map;
+
+/* Obstack for candidate chains.  */
+static struct obstack chain_obstack;
+
+/* Produce a pointer to the IDX'th candidate in the candidate vector.  */
+
+static slsr_cand_t
+lookup_cand (cand_idx idx)
+{
+  return VEC_index (slsr_cand_t, cand_vec, idx - 1);
+}
+
+/* Use the base name from candidate C to look for possible candidates
+   that can serve as a basis for C.  Each potential basis must also
+   appear in a block that dominates the candidate statement and have
+   the same stride and type.  If more than one possible basis exists,
+   the one with highest index in the vector is chosen; this will be
+   the most immediately dominating basis.  */
+
+static int
+find_basis_for_candidate (slsr_cand_t c)
+{
+  cand_chain_t chain;
+  slsr_cand_t basis = NULL;
+
+  gcc_assert (TREE_CODE (c->base_name) == SSA_NAME);
+  chain = base_cand_map[SSA_NAME_VERSION (c->base_name)];
+
+  for (; chain; chain = chain->next)
+    {
+      slsr_cand_t one_basis = chain->cand;
+
+      if (one_basis->kind != c->kind
+	  || !operand_equal_p (one_basis->stride, c->stride, 0)
+	  || !types_compatible_p (one_basis->cand_type, c->cand_type)
+	  || !dominated_by_p (CDI_DOMINATORS,
+			      gimple_bb (c->cand_stmt),
+			      gimple_bb (one_basis->cand_stmt)))
+	continue;
+
+      if (!basis || basis->cand_num < one_basis->cand_num)
+	basis = one_basis;
+    }
+
+  if (basis)
+    {
+      c->sibling = basis->dependent;
+      basis->dependent = c->cand_num;
+      return basis->cand_num;
+    }
+
+  return 0;
+}
+
+/* Record a mapping from the base name of C to C itself, indicating that
+   C may potentially serve as a basis using that base name.  */
+
+static void
+record_potential_basis (slsr_cand_t c)
+{
+  cand_chain_t node, head;
+  int index;
+
+  node = (cand_chain_t) obstack_alloc (&chain_obstack, sizeof (cand_chain));
+  node->base_name = c->base_name;
+  node->cand = c;
+  node->next = NULL;
+  index = SSA_NAME_VERSION (c->base_name);
+  head = base_cand_map[index];
+
+  if (head)
+    {
+      node->next = head->next;
+      head->next = node;
+    }
+  else
+    base_cand_map[index] = node;
+}
+
+/* Allocate storage for a new candidate and initialize its fields.
+   Attempt to find a basis for the candidate.  */
+
+static slsr_cand_t
+alloc_cand_and_find_basis (enum cand_kind kind, gimple gs, tree base, 
+			   double_int index, tree stride, tree ctype,
+			   unsigned savings)
+{
+  slsr_cand_t c = (slsr_cand_t) obstack_alloc (&cand_obstack,
+					       sizeof (slsr_cand));
+  c->cand_stmt = gs;
+  c->base_name = base;
+  c->stride = stride;
+  c->index = index;
+  c->cand_type = ctype;
+  c->kind = kind;
+  c->cand_num = VEC_length (slsr_cand_t, cand_vec) + 1;
+  c->next_interp = 0;
+  c->dependent = 0;
+  c->sibling = 0;
+  c->def_phi = NULL;
+  c->dead_savings = savings;
+
+  VEC_safe_push (slsr_cand_t, heap, cand_vec, c);
+  c->basis = find_basis_for_candidate (c);
+  record_potential_basis (c);
+
+  return c;
+}
+
+/* Determine the target cost of statement GS when compiling according
+   to SPEED.  */
+
+static int
+stmt_cost (gimple gs, bool speed)
+{
+  tree lhs, rhs1, rhs2;
+  enum machine_mode lhs_mode;
+
+  gcc_assert (is_gimple_assign (gs));
+  lhs = gimple_assign_lhs (gs);
+  rhs1 = gimple_assign_rhs1 (gs);
+  lhs_mode = TYPE_MODE (TREE_TYPE (lhs));
+  
+  switch (gimple_assign_rhs_code (gs))
+    {
+    case MULT_EXPR:
+      rhs2 = gimple_assign_rhs2 (gs);
+
+      if (host_integerp (rhs2, 0))
+	return multiply_by_const_cost (TREE_INT_CST_LOW (rhs2), lhs_mode,
+				       speed);
+
+      gcc_assert (TREE_CODE (rhs1) != INTEGER_CST);
+      return multiply_regs_cost (TYPE_MODE (TREE_TYPE (lhs)), speed);
+
+    case PLUS_EXPR:
+    case POINTER_PLUS_EXPR:
+    case MINUS_EXPR:
+      rhs2 = gimple_assign_rhs2 (gs);
+
+      if (host_integerp (rhs2, 0))
+	return add_const_cost (TYPE_MODE (TREE_TYPE (rhs1)), speed);
+
+      gcc_assert (TREE_CODE (rhs1) != INTEGER_CST);
+      return add_regs_cost (lhs_mode, speed);
+
+    case NEGATE_EXPR:
+      return negate_reg_cost (lhs_mode, speed);
+
+    case NOP_EXPR:
+      return extend_or_trunc_reg_cost (TREE_TYPE (lhs), TREE_TYPE (rhs1),
+				       speed);
+
+    /* Note that we don't assign costs to copies that in most cases
+       will go away.  */
+    default:
+      ;
+    }
+  
+  gcc_unreachable ();
+  return 0;
+}
+
+/* Look up the defining statement for BASE_IN and return a pointer
+   to its candidate in the candidate table, if any; otherwise NULL.
+   Only CAND_ADD and CAND_MULT candidates are returned.  */
+
+static slsr_cand_t
+base_cand_from_table (tree base_in)
+{
+  slsr_cand_t *result;
+
+  gimple def = SSA_NAME_DEF_STMT (base_in);
+  if (!def)
+    return (slsr_cand_t) NULL;
+
+  result = (slsr_cand_t *) pointer_map_contains (stmt_cand_map, def);
+  if (!result)
+    return (slsr_cand_t) NULL;
+
+  return *result;
+}
+
+/* Add an entry to the statement-to-candidate mapping.  */
+
+static void
+add_cand_for_stmt (gimple gs, slsr_cand_t c)
+{
+  void **slot = pointer_map_insert (stmt_cand_map, gs);
+  gcc_assert (!*slot);
+  *slot = c;
+}
+
+/* Create a candidate entry for a statement GS, where GS multiplies
+   two SSA names BASE_IN and STRIDE_IN.  Propagate any known information
+   about the two SSA names into the new candidate.  Return the new
+   candidate.  */
+
+static slsr_cand_t
+create_mul_ssa_cand (gimple gs, tree base_in, tree stride_in, bool speed)
+{
+  tree base = NULL_TREE, stride = NULL_TREE, ctype = NULL_TREE;
+  double_int index;
+  unsigned savings = 0;
+  slsr_cand_t c;
+  slsr_cand_t base_cand = base_cand_from_table (base_in);
+
+  /* Look at all interpretations of the base candidate, if necessary,
+     to find information to propagate into this candidate.  */
+  while (base_cand && !base)
+    {
+
+      if (base_cand->kind == CAND_MULT
+	  && operand_equal_p (base_cand->stride, integer_one_node, 0))
+	{
+	  /* Y = (B + i') * 1
+	     X = Y * Z
+	     ================
+	     X = (B + i') * Z  */
+	  base = base_cand->base_name;
+	  index = base_cand->index;
+	  stride = stride_in;
+	  ctype = base_cand->cand_type;
+	  if (has_single_use (base_in))
+	    savings = (base_cand->dead_savings 
+		       + stmt_cost (base_cand->cand_stmt, speed));
+	}
+      else if (base_cand->kind == CAND_ADD
+	       && TREE_CODE (base_cand->stride) == INTEGER_CST)
+	{
+	  /* Y = B + (i' * S), S constant
+	     X = Y * Z
+	     ============================
+	     X = B + ((i' * S) * Z)  */
+	  base = base_cand->base_name;
+	  index = double_int_mul (base_cand->index,
+				  tree_to_double_int (base_cand->stride));
+	  stride = stride_in;
+	  ctype = base_cand->cand_type;
+	  if (has_single_use (base_in))
+	    savings = (base_cand->dead_savings
+		       + stmt_cost (base_cand->cand_stmt, speed));
+	}
+
+      if (base_cand->next_interp)
+	base_cand = lookup_cand (base_cand->next_interp);
+      else
+	base_cand = NULL;
+    }
+
+  if (!base)
+    {
+      /* No interpretations had anything useful to propagate, so
+	 produce X = (Y + 0) * Z.  */
+      base = base_in;
+      index = double_int_zero;
+      stride = stride_in;
+      ctype = TREE_TYPE (SSA_NAME_VAR (base_in));
+    }
+
+  c = alloc_cand_and_find_basis (CAND_MULT, gs, base, index, stride,
+				 ctype, savings);
+  return c;
+}
+
+/* Create a candidate entry for a statement GS, where GS multiplies
+   SSA name BASE_IN by constant STRIDE_IN.  Propagate any known
+   information about BASE_IN into the new candidate.  Return the new
+   candidate.  */
+
+static slsr_cand_t
+create_mul_imm_cand (gimple gs, tree base_in, tree stride_in, bool speed)
+{
+  tree base = NULL_TREE, stride = NULL_TREE, ctype = NULL_TREE;
+  double_int index, temp;
+  unsigned savings = 0;
+  slsr_cand_t c;
+  slsr_cand_t base_cand = base_cand_from_table (base_in);
+
+  /* Look at all interpretations of the base candidate, if necessary,
+     to find information to propagate into this candidate.  */
+  while (base_cand && !base)
+    {
+      if (base_cand->kind == CAND_MULT
+	  && TREE_CODE (base_cand->stride) == INTEGER_CST)
+	{
+	  /* Y = (B + i') * S, S constant
+	     X = Y * c
+	     ============================
+	     X = (B + i') * (S * c)  */
+	  base = base_cand->base_name;
+	  index = base_cand->index;
+	  temp = double_int_mul (tree_to_double_int (base_cand->stride),
+				 tree_to_double_int (stride_in));
+	  stride = double_int_to_tree (TREE_TYPE (stride_in), temp);
+	  ctype = base_cand->cand_type;
+	  if (has_single_use (base_in))
+	    savings = (base_cand->dead_savings 
+		       + stmt_cost (base_cand->cand_stmt, speed));
+	}
+      else if (base_cand->kind == CAND_ADD
+	       && operand_equal_p (base_cand->stride, integer_one_node, 0))
+	{
+	  /* Y = B + (i' * 1)
+	     X = Y * c
+	     ===========================
+	     X = (B + i') * c  */
+	  base = base_cand->base_name;
+	  index = base_cand->index;
+	  stride = stride_in;
+	  ctype = base_cand->cand_type;
+	  if (has_single_use (base_in))
+	    savings = (base_cand->dead_savings
+		       + stmt_cost (base_cand->cand_stmt, speed));
+	}
+      else if (base_cand->kind == CAND_ADD
+	       && double_int_one_p (base_cand->index)
+	       && TREE_CODE (base_cand->stride) == INTEGER_CST)
+	{
+	  /* Y = B + (1 * S), S constant
+	     X = Y * c
+	     ===========================
+	     X = (B + S) * c  */
+	  base = base_cand->base_name;
+	  index = tree_to_double_int (base_cand->stride);
+	  stride = stride_in;
+	  ctype = base_cand->cand_type;
+	  if (has_single_use (base_in))
+	    savings = (base_cand->dead_savings
+		       + stmt_cost (base_cand->cand_stmt, speed));
+	}
+
+      if (base_cand->next_interp)
+	base_cand = lookup_cand (base_cand->next_interp);
+      else
+	base_cand = NULL;
+    }
+
+  if (!base)
+    {
+      /* No interpretations had anything useful to propagate, so
+	 produce X = (Y + 0) * c.  */
+      base = base_in;
+      index = double_int_zero;
+      stride = stride_in;
+      ctype = TREE_TYPE (SSA_NAME_VAR (base_in));
+    }
+
+  c = alloc_cand_and_find_basis (CAND_MULT, gs, base, index, stride,
+				 ctype, savings);
+  return c;
+}
+
+/* Given GS which is a multiply of scalar integers, make an appropriate
+   entry in the candidate table.  If this is a multiply of two SSA names,
+   create two CAND_MULT interpretations and attempt to find a basis for
+   each of them.  Otherwise, create a single CAND_MULT and attempt to
+   find a basis.  */
+
+static void
+slsr_process_mul (gimple gs, tree rhs1, tree rhs2, bool speed)
+{
+  slsr_cand_t c, c2;
+
+  /* If this is a multiply of an SSA name with itself, it is highly
+     unlikely that we will get a strength reduction opportunity, so
+     don't record it as a candidate.  This simplifies the logic for
+     finding a basis, so if this is removed that must be considered.  */
+  if (rhs1 == rhs2)
+    return;
+
+  if (TREE_CODE (rhs2) == SSA_NAME)
+    {
+      /* Record an interpretation of this statement in the candidate table
+	 assuming RHS1 is the base name and RHS2 is the stride.  */
+      c = create_mul_ssa_cand (gs, rhs1, rhs2, speed);
+
+      /* Add the first interpretation to the statement-candidate mapping.  */
+      add_cand_for_stmt (gs, c);
+
+      /* Record another interpretation of this statement assuming RHS1
+	 is the stride and RHS2 is the base name.  */
+      c2 = create_mul_ssa_cand (gs, rhs2, rhs1, speed);
+      c->next_interp = c2->cand_num;
+    }
+  else
+    {
+      /* Record an interpretation for the multiply-immediate.  */
+      c = create_mul_imm_cand (gs, rhs1, rhs2, speed);
+
+      /* Add the interpretation to the statement-candidate mapping.  */
+      add_cand_for_stmt (gs, c);
+    }
+}
+
+/* Create a candidate entry for a statement GS, where GS adds two
+   SSA names BASE_IN and ADDEND_IN if SUBTRACT_P is false, and
+   subtracts ADDEND_IN from BASE_IN otherwise.  Propagate any known
+   information about the two SSA names into the new candidate.
+   Return the new candidate.  */
+
+static slsr_cand_t
+create_add_ssa_cand (gimple gs, tree base_in, tree addend_in,
+		     bool subtract_p, bool speed)
+{
+  tree base = NULL_TREE, stride = NULL_TREE, ctype = NULL;
+  double_int index;
+  unsigned savings = 0;
+  slsr_cand_t c;
+  slsr_cand_t base_cand = base_cand_from_table (base_in);
+  slsr_cand_t addend_cand = base_cand_from_table (addend_in);
+
+  /* The most useful transformation is a multiply-immediate feeding
+     an add or subtract.  Look for that first.  */
+  while (addend_cand && !base)
+    {
+      if (addend_cand->kind == CAND_MULT
+	  && double_int_zero_p (addend_cand->index)
+	  && TREE_CODE (addend_cand->stride) == INTEGER_CST)
+	{
+	  /* Z = (B + 0) * S, S constant
+	     X = Y +/- Z
+	     ===========================
+	     X = Y + ((+/-1 * S) * B)  */
+	  base = base_in;
+	  index = tree_to_double_int (addend_cand->stride);
+	  if (subtract_p)
+	    index = double_int_neg (index);
+	  stride = addend_cand->base_name;
+	  ctype = TREE_TYPE (SSA_NAME_VAR (base_in));
+	  if (has_single_use (addend_in))
+	    savings = (addend_cand->dead_savings
+		       + stmt_cost (addend_cand->cand_stmt, speed));
+	}
+
+      if (addend_cand->next_interp)
+	addend_cand = lookup_cand (addend_cand->next_interp);
+      else
+	addend_cand = NULL;
+    }
+
+  while (base_cand && !base)
+    {
+      if (base_cand->kind == CAND_ADD
+	  && (double_int_zero_p (base_cand->index)
+	      || operand_equal_p (base_cand->stride,
+				  integer_zero_node, 0)))
+	{
+	  /* Y = B + (i' * S), i' * S = 0
+	     X = Y +/- Z
+	     ============================
+	     X = B + (+/-1 * Z)  */
+	  base = base_cand->base_name;
+	  index = subtract_p ? double_int_minus_one : double_int_one;
+	  stride = addend_in;
+	  ctype = base_cand->cand_type;
+	  if (has_single_use (base_in))
+	    savings = (base_cand->dead_savings
+		       + stmt_cost (base_cand->cand_stmt, speed));
+	}
+      else if (subtract_p)
+	{
+	  slsr_cand_t subtrahend_cand = base_cand_from_table (addend_in);
+
+	  while (subtrahend_cand && !base)
+	    {
+	      if (subtrahend_cand->kind == CAND_MULT
+		  && double_int_zero_p (subtrahend_cand->index)
+		  && TREE_CODE (subtrahend_cand->stride) == INTEGER_CST)
+		{
+		  /* Z = (B + 0) * S, S constant
+		     X = Y - Z
+		     ===========================
+		     Value:  X = Y + ((-1 * S) * B)  */
+		  base = base_in;
+		  index = tree_to_double_int (subtrahend_cand->stride);
+		  index = double_int_neg (index);
+		  stride = subtrahend_cand->base_name;
+		  ctype = TREE_TYPE (SSA_NAME_VAR (base_in));
+		  if (has_single_use (addend_in))
+		    savings = (subtrahend_cand->dead_savings 
+			       + stmt_cost (subtrahend_cand->cand_stmt, speed));
+		}
+	      
+	      if (subtrahend_cand->next_interp)
+		subtrahend_cand = lookup_cand (subtrahend_cand->next_interp);
+	      else
+		subtrahend_cand = NULL;
+	    }
+	}
+      
+      if (base_cand->next_interp)
+	base_cand = lookup_cand (base_cand->next_interp);
+      else
+	base_cand = NULL;
+    }
+
+  if (!base)
+    {
+      /* No interpretations had anything useful to propagate, so
+	 produce X = Y + (1 * Z).  */
+      base = base_in;
+      index = subtract_p ? double_int_minus_one : double_int_one;
+      stride = addend_in;
+      ctype = TREE_TYPE (SSA_NAME_VAR (base_in));
+    }
+
+  c = alloc_cand_and_find_basis (CAND_ADD, gs, base, index, stride,
+				 ctype, savings);
+  return c;
+}
+
+/* Create a candidate entry for a statement GS, where GS adds SSA
+   name BASE_IN to constant INDEX_IN.  Propagate any known information
+   about BASE_IN into the new candidate.  Return the new candidate.  */
+
+static slsr_cand_t
+create_add_imm_cand (gimple gs, tree base_in, double_int index_in, bool speed)
+{
+  enum cand_kind kind = CAND_ADD;
+  tree base = NULL_TREE, stride = NULL_TREE, ctype = NULL_TREE;
+  double_int index, multiple;
+  unsigned savings = 0;
+  slsr_cand_t c;
+  slsr_cand_t base_cand = base_cand_from_table (base_in);
+
+  while (base_cand && !base)
+    {
+      bool unsigned_p = TYPE_UNSIGNED (TREE_TYPE (base_cand->stride));
+
+      if (TREE_CODE (base_cand->stride) == INTEGER_CST
+	  && double_int_multiple_of (index_in,
+				     tree_to_double_int (base_cand->stride),
+				     unsigned_p,
+				     &multiple))
+	{
+	  /* Y = (B + i') * S, S constant, c = kS for some integer k
+	     X = Y + c
+	     ============================
+	     X = (B + (i'+ k)) * S  
+	  OR
+	     Y = B + (i' * S), S constant, c = kS for some integer k
+	     X = Y + c
+	     ============================
+	     X = (B + (i'+ k)) * S  */
+	  kind = base_cand->kind;
+	  base = base_cand->base_name;
+	  index = double_int_add (base_cand->index, multiple);
+	  stride = base_cand->stride;
+	  ctype = base_cand->cand_type;
+	  if (has_single_use (base_in))
+	    savings = (base_cand->dead_savings 
+		       + stmt_cost (base_cand->cand_stmt, speed));
+	}
+
+      if (base_cand->next_interp)
+	base_cand = lookup_cand (base_cand->next_interp);
+      else
+	base_cand = NULL;
+    }
+
+  if (!base)
+    {
+      /* No interpretations had anything useful to propagate, so
+	 produce X = Y + (c * 1).  */
+      kind = CAND_ADD;
+      base = base_in;
+      index = index_in;
+      stride = integer_one_node;
+      ctype = TREE_TYPE (SSA_NAME_VAR (base_in));
+    }
+
+  c = alloc_cand_and_find_basis (kind, gs, base, index, stride,
+				 ctype, savings);
+  return c;
+}
+
+/* Given GS which is an add or subtract of scalar integers or pointers,
+   make at least one appropriate entry in the candidate table.  */
+
+static void
+slsr_process_add (gimple gs, tree rhs1, tree rhs2, bool speed)
+{
+  bool subtract_p = gimple_assign_rhs_code (gs) == MINUS_EXPR;
+  slsr_cand_t c = NULL, c2;
+
+  if (TREE_CODE (rhs2) == SSA_NAME)
+    {
+      /* First record an interpretation assuming RHS1 is the base name
+	 and RHS2 is the stride.  But it doesn't make sense for the
+	 stride to be a pointer, so don't record a candidate in that case.  */
+      if (!POINTER_TYPE_P (TREE_TYPE (SSA_NAME_VAR (rhs2))))
+	{
+	  c = create_add_ssa_cand (gs, rhs1, rhs2, subtract_p, speed);
+
+	  /* Add the first interpretation to the statement-candidate
+	     mapping.  */
+	  add_cand_for_stmt (gs, c);
+	}
+
+      /* If the two RHS operands are identical, or this is a subtract,
+	 we're done.  */
+      if (operand_equal_p (rhs1, rhs2, 0) || subtract_p)
+	return;
+
+      /* Otherwise, record another interpretation assuming RHS2 is the
+	 base name and RHS1 is the stride, again provided that the
+	 stride is not a pointer.  */
+      if (!POINTER_TYPE_P (TREE_TYPE (SSA_NAME_VAR (rhs1))))
+	{
+	  c2 = create_add_ssa_cand (gs, rhs2, rhs1, false, speed);
+	  if (c)
+	    c->next_interp = c2->cand_num;
+	  else
+	    add_cand_for_stmt (gs, c2);
+	}
+    }
+  else
+    {
+      double_int index;
+
+      /* Record an interpretation for the add-immediate.  */
+      index = tree_to_double_int (rhs2);
+      if (subtract_p)
+	index = double_int_neg (index);
+
+      c = create_add_imm_cand (gs, rhs1, index, speed);
+
+      /* Add the interpretation to the statement-candidate mapping.  */
+      add_cand_for_stmt (gs, c);
+    }
+}
+
+/* Given GS which is a negate of a scalar integer, make an appropriate
+   entry in the candidate table.  A negate is equivalent to a multiply
+   by -1.  */
+
+static void
+slsr_process_neg (gimple gs, tree rhs1, bool speed)
+{
+  /* Record a CAND_MULT interpretation for the multiply by -1.  */
+  slsr_cand_t c = create_mul_imm_cand (gs, rhs1, integer_minus_one_node, speed);
+
+  /* Add the interpretation to the statement-candidate mapping.  */
+  add_cand_for_stmt (gs, c);
+}
+
+/* Return TRUE if GS is a statement that defines an SSA name from
+   a conversion and is legal for us to combine with an add and multiply
+   in the candidate table.  For example, suppose we have:
+
+     A = B + i;
+     C = (type) A;
+     D = C * S;
+
+   Without the type-cast, we would create a CAND_MULT for D with base B,
+   index i, and stride S.  We want to record this candidate only if it
+   is equivalent to apply the type cast following the multiply:
+
+     A = B + i;
+     E = A * S;
+     D = (type) E;
+
+   We will record the type with the candidate for D.  This allows us
+   to use a similar previous candidate as a basis.  If we have earlier seen
+
+     A' = B + i';
+     C' = (type) A';
+     D' = C' * S;
+
+   we can replace D with
+
+     D = D' + (i - i') * S;
+
+   But if moving the type-cast would change semantics, we mustn't do this.
+
+   This is legitimate for casts from a non-wrapping integral type to
+   any integral type of the same or larger size.  It is not legitimate
+   to convert a wrapping type to a non-wrapping type, or to a wrapping
+   type of a different size.  I.e., with a wrapping type, we must
+   assume that the addition B + i could wrap, in which case performing
+   the multiply before or after one of the "illegal" type casts will
+   have different semantics.  */
+
+static bool
+legal_cast_p (gimple gs, tree rhs)
+{
+  tree lhs, lhs_type, rhs_type;
+  unsigned lhs_size, rhs_size;
+  bool lhs_wraps, rhs_wraps;
+
+  if (!is_gimple_assign (gs)
+      || !CONVERT_EXPR_CODE_P (gimple_assign_rhs_code (gs)))
+    return false;
+
+  lhs = gimple_assign_lhs (gs);
+  lhs_type = TREE_TYPE (lhs);
+  rhs_type = TREE_TYPE (rhs);
+  lhs_size = TYPE_PRECISION (lhs_type);
+  rhs_size = TYPE_PRECISION (rhs_type);
+  lhs_wraps = TYPE_OVERFLOW_WRAPS (lhs_type);
+  rhs_wraps = TYPE_OVERFLOW_WRAPS (rhs_type);
+
+  if (lhs_size < rhs_size
+      || (rhs_wraps && !lhs_wraps)
+      || (rhs_wraps && lhs_wraps && rhs_size != lhs_size))
+    return false;
+
+  return true;
+}
+
+/* Given GS which is a cast to a scalar integer type, determine whether
+   the cast is legal for strength reduction.  If so, make at least one
+   appropriate entry in the candidate table.  */
+
+static void
+slsr_process_cast (gimple gs, tree rhs1, bool speed)
+{
+  tree lhs, ctype;
+  slsr_cand_t base_cand, c, c2;
+  unsigned savings = 0;
+
+  if (!legal_cast_p (gs, rhs1))
+    return;
+
+  lhs = gimple_assign_lhs (gs);
+  base_cand = base_cand_from_table (rhs1);
+  ctype = TREE_TYPE (lhs);
+
+  if (base_cand)
+    {
+      while (base_cand)
+	{
+	  /* Propagate all data from the base candidate except the type,
+	     which comes from the cast, and the base candidate's cast,
+	     which is no longer applicable.  */
+	  if (has_single_use (rhs1))
+	    savings = (base_cand->dead_savings 
+		       + stmt_cost (base_cand->cand_stmt, speed));
+
+	  c = alloc_cand_and_find_basis (base_cand->kind, gs,
+					 base_cand->base_name,
+					 base_cand->index, base_cand->stride,
+					 ctype, savings);
+	  if (base_cand->next_interp)
+	    base_cand = lookup_cand (base_cand->next_interp);
+	  else
+	    base_cand = NULL;
+	}
+    }
+  else 
+    {
+      /* If nothing is known about the RHS, create fresh CAND_ADD and
+	 CAND_MULT interpretations:
+
+	 X = Y + (0 * 1)
+	 X = (Y + 0) * 1
+
+	 The first of these is somewhat arbitrary, but the choice of
+	 1 for the stride simplifies the logic for propagating casts
+	 into their uses.  */
+      c = alloc_cand_and_find_basis (CAND_ADD, gs, rhs1, double_int_zero,
+				     integer_one_node, ctype, 0);
+      c2 = alloc_cand_and_find_basis (CAND_MULT, gs, rhs1, double_int_zero,
+				      integer_one_node, ctype, 0);
+      c->next_interp = c2->cand_num;
+    }
+
+  /* Add the first (or only) interpretation to the statement-candidate
+     mapping.  */
+  add_cand_for_stmt (gs, c);
+}
+
+/* Given GS which is a copy of a scalar integer type, make at least one
+   appropriate entry in the candidate table.
+
+   This interface is included for completeness, but is unnecessary
+   if this pass immediately follows a pass that performs copy 
+   propagation, such as DOM.  */
+
+static void
+slsr_process_copy (gimple gs, tree rhs1, bool speed)
+{
+  slsr_cand_t base_cand, c, c2;
+  unsigned savings = 0;
+
+  base_cand = base_cand_from_table (rhs1);
+
+  if (base_cand)
+    {
+      while (base_cand)
+	{
+	  /* Propagate all data from the base candidate.  */
+	  if (has_single_use (rhs1))
+	    savings = (base_cand->dead_savings 
+		       + stmt_cost (base_cand->cand_stmt, speed));
+
+	  c = alloc_cand_and_find_basis (base_cand->kind, gs,
+					 base_cand->base_name,
+					 base_cand->index, base_cand->stride,
+					 base_cand->cand_type, savings);
+	  if (base_cand->next_interp)
+	    base_cand = lookup_cand (base_cand->next_interp);
+	  else
+	    base_cand = NULL;
+	}
+    }
+  else 
+    {
+      /* If nothing is known about the RHS, create fresh CAND_ADD and
+	 CAND_MULT interpretations:
+
+	 X = Y + (0 * 1)
+	 X = (Y + 0) * 1
+
+	 The first of these is somewhat arbitrary, but the choice of
+	 1 for the stride simplifies the logic for propagating casts
+	 into their uses.  */
+      c = alloc_cand_and_find_basis (CAND_ADD, gs, rhs1, double_int_zero,
+				     integer_one_node, TREE_TYPE (rhs1), 0);
+      c2 = alloc_cand_and_find_basis (CAND_MULT, gs, rhs1, double_int_zero,
+				      integer_one_node, TREE_TYPE (rhs1), 0);
+      c->next_interp = c2->cand_num;
+    }
+
+  /* Add the first (or only) interpretation to the statement-candidate
+     mapping.  */
+  add_cand_for_stmt (gs, c);
+}
+
+/* Find strength-reduction candidates in block BB.  */
+
+static void
+find_candidates_in_block (struct dom_walk_data *walk_data ATTRIBUTE_UNUSED,
+			  basic_block bb)
+{
+  bool speed = optimize_bb_for_speed_p (bb);
+  gimple_stmt_iterator gsi;
+
+  for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
+    {
+      gimple gs = gsi_stmt (gsi);
+
+      if (is_gimple_assign (gs)
+	  && SCALAR_INT_MODE_P (TYPE_MODE (TREE_TYPE (gimple_assign_lhs (gs)))))
+	{
+	  tree rhs1 = NULL_TREE, rhs2 = NULL_TREE;
+
+	  switch (gimple_assign_rhs_code (gs))
+	    {
+	    case MULT_EXPR:
+	    case PLUS_EXPR:
+	      rhs1 = gimple_assign_rhs1 (gs);
+	      rhs2 = gimple_assign_rhs2 (gs);
+	      /* Should never happen, but currently some buggy situations
+		 in earlier phases put constants in rhs1.  */
+	      if (TREE_CODE (rhs1) != SSA_NAME)
+		continue;
+	      break;
+
+	    /* Possible future opportunity: rhs1 of a ptr+ can be
+	       an ADDR_EXPR.  */
+	    case POINTER_PLUS_EXPR:
+	    case MINUS_EXPR:
+	      rhs2 = gimple_assign_rhs2 (gs);
+	      /* Fall-through.  */
+
+	    case NOP_EXPR:
+	    case MODIFY_EXPR:
+	    case NEGATE_EXPR:
+	      rhs1 = gimple_assign_rhs1 (gs);
+	      if (TREE_CODE (rhs1) != SSA_NAME)
+		continue;
+	      break;
+
+	    default:
+	      ;
+	    }
+
+	  switch (gimple_assign_rhs_code (gs))
+	    {
+	    case MULT_EXPR:
+	      slsr_process_mul (gs, rhs1, rhs2, speed);
+	      break;
+
+	    case PLUS_EXPR:
+	    case POINTER_PLUS_EXPR:
+	    case MINUS_EXPR:
+	      slsr_process_add (gs, rhs1, rhs2, speed);
+	      break;
+
+	    case NEGATE_EXPR:
+	      slsr_process_neg (gs, rhs1, speed);
+	      break;
+
+	    case NOP_EXPR:
+	      slsr_process_cast (gs, rhs1, speed);
+	      break;
+
+	    case MODIFY_EXPR:
+	      slsr_process_copy (gs, rhs1, speed);
+	      break;
+
+	    default:
+	      ;
+	    }
+	}
+    }
+}
+
+/* Dump a candidate for debug.  */
+
+static void
+dump_candidate (slsr_cand_t c)
+{
+  fprintf (dump_file, "%3d  [%d] ", c->cand_num,
+	   gimple_bb (c->cand_stmt)->index);
+  print_gimple_stmt (dump_file, c->cand_stmt, 0, 0);
+  switch (c->kind)
+    {
+    case CAND_MULT:
+      fputs ("     MULT : (", dump_file);
+      print_generic_expr (dump_file, c->base_name, 0);
+      fputs (" + ", dump_file);
+      dump_double_int (dump_file, c->index, false);
+      fputs (") * ", dump_file);
+      print_generic_expr (dump_file, c->stride, 0);
+      fputs (" : ", dump_file);
+      break;
+    case CAND_ADD:
+      fputs ("     ADD  : ", dump_file);
+      print_generic_expr (dump_file, c->base_name, 0);
+      fputs (" + (", dump_file);
+      dump_double_int (dump_file, c->index, false);
+      fputs (" * ", dump_file);
+      print_generic_expr (dump_file, c->stride, 0);
+      fputs (") : ", dump_file);
+      break;
+    default:
+      gcc_unreachable ();
+    }
+  print_generic_expr (dump_file, c->cand_type, 0);
+  fprintf (dump_file, "\n     basis: %d  dependent: %d  sibling: %d\n",
+	   c->basis, c->dependent, c->sibling);
+  fprintf (dump_file, "     next-interp: %d  dead-savings: %d\n",
+	   c->next_interp, c->dead_savings);
+  if (c->def_phi)
+    {
+      fputs ("     phi:  ", dump_file);
+      print_gimple_stmt (dump_file, c->def_phi, 0, 0);
+    }
+  fputs ("\n", dump_file);
+}
+
+/* Dump the candidate vector for debug.  */
+
+static void
+dump_cand_vec (void)
+{
+  unsigned i;
+  slsr_cand_t c;
+
+  fprintf (dump_file, "\nStrength reduction candidate vector:\n\n");
+  
+  FOR_EACH_VEC_ELT (slsr_cand_t, cand_vec, i, c)
+    dump_candidate (c);
+}
+
+/* Dump the candidate chains.  */
+
+static void
+dump_cand_chains (void)
+{
+  unsigned i;
+
+  fprintf (dump_file, "\nStrength reduction candidate chains:\n\n");
+
+  for (i = 0; i < num_ssa_names; i++)
+    {
+      const_cand_chain_t chain = base_cand_map[i];
+
+      if (chain)
+	{
+	  cand_chain_t p;
+
+	  print_generic_expr (dump_file, chain->base_name, 0);
+	  fprintf (dump_file, " -> %d", chain->cand->cand_num);
+
+	  for (p = chain->next; p; p = p->next)
+	    fprintf (dump_file, " -> %d", p->cand->cand_num);
+
+	  fputs ("\n", dump_file);
+	}
+    }
+
+  fputs ("\n", dump_file);
+}
+
+
+/* Recursive helper for unconditional_cands_with_known_stride_p.
+   Returns TRUE iff C, its siblings, and its dependents are all
+   unconditional candidates.  */
+
+static bool
+unconditional_cands (slsr_cand_t c)
+{
+  if (c->def_phi)
+    return false;
+
+  if (c->sibling && !unconditional_cands (lookup_cand (c->sibling)))
+    return false;
+
+  if (c->dependent && !unconditional_cands (lookup_cand (c->dependent)))
+    return false;
+
+  return true;
+}
+
+/* Determine whether or not the tree of candidates rooted at
+   ROOT consists entirely of unconditional increments with
+   an INTEGER_CST stride.  */
+
+static bool
+unconditional_cands_with_known_stride_p (slsr_cand_t root)
+{
+  /* The stride is identical for all related candidates, so
+     check it once.  */
+  if (TREE_CODE (root->stride) != INTEGER_CST)
+    return false;
+
+  return unconditional_cands (lookup_cand (root->dependent));
+}
+
+/* Calculate the increment required for candidate C relative to 
+   its basis.  */
+
+static double_int
+cand_increment (slsr_cand_t c)
+{
+  slsr_cand_t basis;
+
+  /* If the candidate doesn't have a basis, just return its own
+     index.  This is useful in record_increments to help us find
+     an existing initializer.  */
+  if (!c->basis)
+    return c->index;
+
+  basis = lookup_cand (c->basis);
+  gcc_assert (operand_equal_p (c->base_name, basis->base_name, 0));
+  return double_int_sub (c->index, basis->index);
+}
+
+/* Return TRUE iff candidate C has already been replaced under
+   another interpretation.  */
+
+static inline bool
+cand_already_replaced (slsr_cand_t c)
+{
+  return (gimple_bb (c->cand_stmt) == 0);
+}
+
+/* Helper routine for replace_dependents, doing the work for a 
+   single candidate C.  */
+
+static void
+replace_dependent (slsr_cand_t c, enum tree_code cand_code)
+{
+  double_int stride = tree_to_double_int (c->stride);
+  double_int bump = double_int_mul (cand_increment (c), stride);
+  gimple stmt_to_print = NULL;
+  slsr_cand_t basis;
+  tree basis_name, incr_type, bump_tree;
+  enum tree_code code;
+  
+  /* It is highly unlikely, but possible, that the resulting
+     bump doesn't fit in a HWI.  Abandon the replacement
+     in this case.  Restriction to signed HWI is conservative
+     for unsigned types but allows for safe negation without
+     twisted logic.  */
+  if (!double_int_fits_in_shwi_p (bump))
+    return;
+
+  basis = lookup_cand (c->basis);
+  basis_name = gimple_assign_lhs (basis->cand_stmt);
+  incr_type = TREE_TYPE (gimple_assign_rhs1 (c->cand_stmt));
+  code = PLUS_EXPR;
+
+  if (double_int_negative_p (bump))
+    {
+      code = MINUS_EXPR;
+      bump = double_int_neg (bump);
+    }
+
+  bump_tree = double_int_to_tree (incr_type, bump);
+
+  if (dump_file && (dump_flags & TDF_DETAILS))
+    {
+      fputs ("Replacing: ", dump_file);
+      print_gimple_stmt (dump_file, c->cand_stmt, 0, 0);
+    }
+
+  if (double_int_zero_p (bump))
+    {
+      tree lhs = gimple_assign_lhs (c->cand_stmt);
+      gimple copy_stmt = gimple_build_assign (lhs, basis_name);
+      gimple_stmt_iterator gsi = gsi_for_stmt (c->cand_stmt);
+      gimple_set_location (copy_stmt, gimple_location (c->cand_stmt));
+      gsi_replace (&gsi, copy_stmt, false);
+      if (dump_file && (dump_flags & TDF_DETAILS))
+	stmt_to_print = copy_stmt;
+    }
+  else
+    {
+      tree rhs1 = gimple_assign_rhs1 (c->cand_stmt);
+      tree rhs2 = gimple_assign_rhs2 (c->cand_stmt);
+      if (cand_code != NEGATE_EXPR
+	  && ((operand_equal_p (rhs1, basis_name, 0)
+	       && operand_equal_p (rhs2, bump_tree, 0))
+	      || (operand_equal_p (rhs1, bump_tree, 0)
+		  && operand_equal_p (rhs2, basis_name, 0))))
+	{
+	  if (dump_file && (dump_flags & TDF_DETAILS))
+	    {
+	      fputs ("(duplicate, not actually replacing)", dump_file);
+	      stmt_to_print = c->cand_stmt;
+	    }
+	}
+      else
+	{
+	  gimple_stmt_iterator gsi = gsi_for_stmt (c->cand_stmt);
+	  gimple_assign_set_rhs_with_ops (&gsi, code, basis_name, bump_tree);
+	  update_stmt (gsi_stmt (gsi));
+	  if (dump_file && (dump_flags & TDF_DETAILS))
+	    stmt_to_print = gsi_stmt (gsi);
+	}
+    }
+  
+  if (dump_file && (dump_flags & TDF_DETAILS))
+    {
+      fputs ("With: ", dump_file);
+      print_gimple_stmt (dump_file, stmt_to_print, 0, 0);
+      fputs ("\n", dump_file);
+    }
+}
+
+/* Replace candidate C, each sibling of candidate C, and each
+   dependent of candidate C with an add or subtract.  Note that we
+   only operate on CAND_MULTs with known strides, so we will never
+   generate a POINTER_PLUS_EXPR.  Each candidate X = (B + i) * S is
+   replaced by X = Y + ((i - i') * S), as described in the module
+   commentary.  The folded value ((i - i') * S) is referred to here
+   as the "bump."  */
+
+static void
+replace_dependents (slsr_cand_t c)
+{
+  enum tree_code cand_code = gimple_assign_rhs_code (c->cand_stmt);
+
+  /* It is not useful to replace casts, copies, or adds of an SSA name
+     and a constant.  Also skip candidates that have already been
+     replaced under another interpretation.  */
+  if (cand_code != MODIFY_EXPR
+      && cand_code != NOP_EXPR
+      && c->kind == CAND_MULT
+      && !cand_already_replaced (c))
+    replace_dependent (c, cand_code);
+
+  if (c->sibling)
+    replace_dependents (lookup_cand (c->sibling));
+
+  if (c->dependent)
+    replace_dependents (lookup_cand (c->dependent));
+}
+
+/* Analyze costs of related candidates in the candidate vector,
+   and make beneficial replacements.  */
+
+static void
+analyze_candidates_and_replace (void)
+{
+  unsigned i;
+  slsr_cand_t c;
+
+  /* Each candidate that has a null basis and a non-null
+     dependent is the root of a tree of related statements.
+     Analyze each tree to determine a subset of those
+     statements that can be replaced with maximum benefit.  */
+  FOR_EACH_VEC_ELT (slsr_cand_t, cand_vec, i, c)
+    {
+      slsr_cand_t first_dep;
+
+      if (c->basis != 0 || c->dependent == 0)
+	continue;
+
+      if (dump_file && (dump_flags & TDF_DETAILS))
+	fprintf (dump_file, "\nProcessing dependency tree rooted at %d.\n",
+		 c->cand_num);
+
+      first_dep = lookup_cand (c->dependent);
+
+      /* If the common stride of all related candidates is a
+	 known constant, and none of these has a phi-dependence,
+	 then all replacements are considered profitable.
+	 Each replaces a multiply by a single add, with the
+	 possibility that a feeding add also goes dead as a
+	 result.  */
+      if (unconditional_cands_with_known_stride_p (c))
+	replace_dependents (first_dep);
+
+      /* TODO:  When the stride is an SSA name, it may still be
+	 profitable to replace some or all of the dependent
+	 candidates, depending on whether the introduced increments
+	 can be reused, or are less expensive to calculate than
+	 the replaced statements.  */
+
+      /* TODO:  Strength-reduce data references with implicit
+	 multiplication in their addressing expressions.  */
+
+      /* TODO:  When conditional increments occur so that a 
+	 candidate is dependent upon a phi-basis, the cost of
+	 introducing a temporary must be accounted for.  */
+    }
+}
+
+static unsigned
+execute_strength_reduction (void)
+{
+  struct dom_walk_data walk_data;
+
+  /* Create the obstack where candidates will reside.  */
+  gcc_obstack_init (&cand_obstack);
+
+  /* Allocate the candidate vector.  */
+  cand_vec = VEC_alloc (slsr_cand_t, heap, 128);
+
+  /* Allocate the mapping from statements to candidate indices.  */
+  stmt_cand_map = pointer_map_create ();
+
+  /* Create the obstack where candidate chains will reside.  */
+  gcc_obstack_init (&chain_obstack);
+
+  /* Allocate the mapping from base names to candidate chains.  */
+  base_cand_map = XNEWVEC (cand_chain_t, num_ssa_names);
+  memset (base_cand_map, 0, num_ssa_names * sizeof (cand_chain_t));
+
+  /* Initialize the loop optimizer.  We need to detect flow across
+     back edges, and this gives us dominator information as well.  */
+  loop_optimizer_init (AVOID_CFG_MODIFICATIONS);
+
+  /* Initialize costs tables in IVOPTS.  */
+  initialize_costs ();
+
+  /* Set up callbacks for the generic dominator tree walker.  */
+  walk_data.dom_direction = CDI_DOMINATORS;
+  walk_data.initialize_block_local_data = NULL;
+  walk_data.before_dom_children = find_candidates_in_block;
+  walk_data.after_dom_children = NULL;
+  walk_data.global_data = NULL;
+  walk_data.block_local_data_size = 0;
+  init_walk_dominator_tree (&walk_data);
+
+  /* Walk the CFG in predominator order looking for strength reduction
+     candidates.  */
+  walk_dominator_tree (&walk_data, ENTRY_BLOCK_PTR);
+
+  if (dump_file && (dump_flags & TDF_DETAILS))
+    {
+      dump_cand_vec ();
+      dump_cand_chains ();
+    }
+
+  /* Analyze costs and make appropriate replacements.  */
+  analyze_candidates_and_replace ();
+
+  /* Free resources.  */
+  fini_walk_dominator_tree (&walk_data);
+  loop_optimizer_finalize ();
+  free (base_cand_map);
+  obstack_free (&chain_obstack, NULL);
+  pointer_map_destroy (stmt_cand_map);
+  VEC_free (slsr_cand_t, heap, cand_vec);
+  obstack_free (&cand_obstack, NULL);
+  finalize_costs ();
+
+  return 0;
+}
+
+static bool
+gate_strength_reduction (void)
+{
+  return optimize > 0;
+}
+
+struct gimple_opt_pass pass_strength_reduction =
+{
+ {
+  GIMPLE_PASS,
+  "slsr",				/* name */
+  gate_strength_reduction,		/* gate */
+  execute_strength_reduction,		/* execute */
+  NULL,					/* sub */
+  NULL,					/* next */
+  0,					/* static_pass_number */
+  TV_GIMPLE_SLSR,			/* tv_id */
+  PROP_cfg | PROP_ssa,			/* properties_required */
+  0,					/* properties_provided */
+  0,					/* properties_destroyed */
+  0,					/* todo_flags_start */
+  TODO_verify_ssa			/* todo_flags_finish */
+ }
+};