GCC Middle and Back End API Reference
tree-ssa-pre.c File Reference

Data Structures

union  pre_expr_union_d
struct  pre_expr_d
struct  bitmap_set
struct  bb_bitmap_sets
struct  expr_pred_trans_d
class  eliminate_dom_walker


typedef union pre_expr_union_d pre_expr_union
typedef pre_expr_dpre_expr
typedef struct bitmap_setbitmap_set_t
typedef struct bb_bitmap_setsbb_value_sets_t
typedef expr_pred_trans_dexpr_pred_trans_t
typedef struct expr_pred_trans_dconst_expr_pred_trans_t


enum  pre_expr_kind { NAME, NARY, REFERENCE, CONSTANT }


static unsigned int alloc_expression_id ()
static unsigned int get_expression_id ()
static unsigned int lookup_expression_id ()
static unsigned int get_or_alloc_expression_id ()
static pre_expr expression_for_id ()
static void clear_expression_ids ()
static pre_expr get_or_alloc_expr_for_name ()
static pre_expr bitmap_find_leader (bitmap_set_t, unsigned int)
static void bitmap_value_insert_into_set (bitmap_set_t, pre_expr)
static void bitmap_value_replace_in_set (bitmap_set_t, pre_expr)
static void bitmap_set_copy (bitmap_set_t, bitmap_set_t)
static bool bitmap_set_contains_value (bitmap_set_t, unsigned int)
static void bitmap_insert_into_set (bitmap_set_t, pre_expr)
static void bitmap_insert_into_set_1 (bitmap_set_t, pre_expr, unsigned int, bool)
static bitmap_set_t bitmap_set_new (void)
static tree create_expression_by_pieces (basic_block, pre_expr, gimple_seq *, tree)
static tree find_or_generate_expression (basic_block, tree, gimple_seq *)
static unsigned int get_expr_value_id (pre_expr)
static bool phi_trans_add ()
static void add_to_value ()
static unsigned int get_expr_value_id ()
static tree sccvn_valnum_from_value_id ()
static void bitmap_remove_from_set ()
static void bitmap_insert_into_set ()
static void bitmap_set_copy ()
static void bitmap_set_free ()
static vec< pre_exprsorted_array_from_bitmap_set ()
static void bitmap_set_and ()
static bitmap_set_t bitmap_set_subtract ()
static void bitmap_set_subtract_values ()
static bool bitmap_set_contains_value ()
static bool bitmap_set_contains_expr ()
static void bitmap_set_replace_value (bitmap_set_t set, unsigned int lookfor, const pre_expr expr)
static bool bitmap_set_equal ()
static void bitmap_value_replace_in_set ()
static void bitmap_value_insert_into_set ()
static void print_pre_expr ()
void debug_pre_expr (pre_expr)
DEBUG_FUNCTION void debug_pre_expr ()
static void print_bitmap_set (FILE *outfile, bitmap_set_t set, const char *setname, int blockindex)
void debug_bitmap_set (bitmap_set_t)
DEBUG_FUNCTION void debug_bitmap_set ()
void debug_bitmap_sets_for (basic_block)
DEBUG_FUNCTION void debug_bitmap_sets_for ()
static void print_value_expressions ()
DEBUG_FUNCTION void debug_value_expressions ()
static pre_expr get_or_alloc_expr_for_constant ()
static tree get_constant_for_value_id ()
static pre_expr get_or_alloc_expr_for ()
static pre_expr fully_constant_expression ()
static tree translate_vuse_through_block (vec< vn_reference_op_s > operands, alias_set_type set, tree type, tree vuse, basic_block phiblock, basic_block block, bool *same_valid)
static pre_expr find_leader_in_sets ()
static tree get_expr_type ()
static tree get_representative_for ()
static pre_expr phi_translate (pre_expr expr, bitmap_set_t set1, bitmap_set_t set2, basic_block pred, basic_block phiblock)
static pre_expr phi_translate_1 (pre_expr expr, bitmap_set_t set1, bitmap_set_t set2, basic_block pred, basic_block phiblock)
static void phi_translate_set (bitmap_set_t dest, bitmap_set_t set, basic_block pred, basic_block phiblock)
static pre_expr bitmap_find_leader ()
static bool value_dies_in_block_x ()
static bool op_valid_in_sets ()
static bool valid_in_sets (bitmap_set_t set1, bitmap_set_t set2, pre_expr expr, basic_block block)
static void dependent_clean ()
static void clean ()
static void prune_clobbered_mems ()
static bool defer_or_phi_translate_block (bitmap_set_t dest, bitmap_set_t source, basic_block block, basic_block phiblock)
static bool compute_antic_aux ()
static bool compute_partial_antic_aux (basic_block block, bool block_has_abnormal_pred_edge)
static void compute_antic ()
static tree create_component_ref_by_pieces_1 (basic_block block, vn_reference_t ref, unsigned int *operand, gimple_seq *stmts)
static tree create_component_ref_by_pieces (basic_block block, vn_reference_t ref, gimple_seq *stmts)
static tree find_or_generate_expression ()
static bool inhibit_phi_insertion ()
static bool insert_into_preds_of_block (basic_block block, unsigned int exprnum, vec< pre_expr > avail)
static bool do_regular_insertion ()
static bool do_partial_partial_insertion ()
static bool insert_aux ()
static void insert ()
static void compute_avail ()
static tree eliminate_avail ()
static void eliminate_push_avail ()
static tree eliminate_insert ()
static unsigned int eliminate ()
static unsigned fini_eliminate ()
static gimple mark_operand_necessary ()
static void remove_dead_inserted_code ()
static void init_pre ()
static void fini_pre ()
static unsigned int do_pre ()
static bool gate_pre ()
gimple_opt_passmake_pass_pre ()
static unsigned int execute_fre ()
static bool gate_fre ()
gimple_opt_passmake_pass_fre ()


static unsigned int next_expression_id
static vec< pre_exprexpressions
static hash_table< pre_expr_dexpression_to_id
static vec< unsigned > name_to_id
static alloc_pool pre_expr_pool
static vec< bitmapvalue_expressions
static int * postorder
static int postorder_num
static struct { ... }  pre_stats
static bool do_partial_partial
static alloc_pool bitmap_set_pool
static bitmap_obstack grand_bitmap_obstack
static bitmap need_eh_cleanup
static bitmap need_ab_cleanup
static hash_table
< expr_pred_trans_d
static sbitmap has_abnormal_preds
static sbitmap changed_blocks
static bitmap inserted_exprs
static vec< gimpleel_to_remove
static vec< gimpleel_to_update
static unsigned int el_todo
static vec< treeel_avail
static vec< treeel_avail_stack

Typedef Documentation

typedef struct bb_bitmap_sets * bb_value_sets_t
   Sets that we need to keep track of.  
typedef struct bitmap_set * bitmap_set_t
   An unordered bitmap set.  One bitmap tracks values, the other,
   A three tuple {e, pred, v} used to cache phi translations in the
typedef pre_expr_d * pre_expr

Enumeration Type Documentation


SSA-PRE for trees. Copyright (C) 2001-2013 Free Software Foundation, Inc. Contributed by Daniel Berlin dan@d.nosp@m.berl.nosp@m.in.or.nosp@m.g and Steven Bosscher steve.nosp@m.nb@s.nosp@m.use.d.nosp@m.e

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/.


   1. Avail sets can be shared by making an avail_find_leader that
      walks up the dominator tree and looks in those avail sets.
      This might affect code optimality, it's unclear right now.
   2. Strength reduction can be performed by anticipating expressions
      we can repair later on.
   3. We can do back-substitution or smarter value numbering to catch
      commutative expressions split up over multiple statements.
   For ease of terminology, "expression node" in the below refers to
   every expression node but GIMPLE_ASSIGN, because GIMPLE_ASSIGNs
   represent the actual statement containing the expressions we care about,
   and we cache the value number by putting it in the expression.  
   Basic algorithm

   First we walk the statements to generate the AVAIL sets, the
   EXP_GEN sets, and the tmp_gen sets.  EXP_GEN sets represent the
   generation of values/expressions by a given block.  We use them
   when computing the ANTIC sets.  The AVAIL sets consist of
   SSA_NAME's that represent values, so we know what values are
   available in what blocks.  AVAIL is a forward dataflow problem.  In
   SSA, values are never killed, so we don't need a kill set, or a
   fixpoint iteration, in order to calculate the AVAIL sets.  In
   traditional parlance, AVAIL sets tell us the downsafety of the

   Next, we generate the ANTIC sets.  These sets represent the
   anticipatable expressions.  ANTIC is a backwards dataflow
   problem.  An expression is anticipatable in a given block if it could
   be generated in that block.  This means that if we had to perform
   an insertion in that block, of the value of that expression, we
   could.  Calculating the ANTIC sets requires phi translation of
   expressions, because the flow goes backwards through phis.  We must
   iterate to a fixpoint of the ANTIC sets, because we have a kill
   set.  Even in SSA form, values are not live over the entire
   function, only from their definition point onwards.  So we have to
   remove values from the ANTIC set once we go past the definition
   point of the leaders that make them up.
   compute_antic/compute_antic_aux performs this computation.

   Third, we perform insertions to make partially redundant
   expressions fully redundant.

   An expression is partially redundant (excluding partial
   anticipation) if:

   1. It is AVAIL in some, but not all, of the predecessors of a
      given block.
   2. It is ANTIC in all the predecessors.

   In order to make it fully redundant, we insert the expression into
   the predecessors where it is not available, but is ANTIC.

   For the partial anticipation case, we only perform insertion if it
   is partially anticipated in some block, and fully available in all
   of the predecessors.

   performs these steps.

   Fourth, we eliminate fully redundant expressions.
   This is a simple statement walk that replaces redundant
   calculations with the now available values.  
   Representations of value numbers:

   Value numbers are represented by a representative SSA_NAME.  We
   will create fake SSA_NAME's in situations where we need a
   representative but do not have one (because it is a complex
   expression).  In order to facilitate storing the value numbers in
   bitmaps, and keep the number of wasted SSA_NAME's down, we also
   associate a value_id with each value number, and create full blown
   ssa_name's only where we actually need them (IE in operands of
   existing expressions).

   Theoretically you could replace all the value_id's with
   SSA_NAME_VERSION, but this would allocate a large number of
   SSA_NAME's (which are each > 30 bytes) just to get a 4 byte number.
   It would also require an additional indirection at each point we
   use the value id.  
   Representation of expressions on value numbers:

   Expressions consisting of value numbers are represented the same
   way as our VN internally represents them, with an additional
   "pre_expr" wrapping around them in order to facilitate storing all
   of the expressions in the same sets.  
   Representation of sets:

   The dataflow sets do not need to be sorted in any particular order
   for the majority of their lifetime, are simply represented as two
   bitmaps, one that keeps track of values present in the set, and one
   that keeps track of expressions present in the set.

   When we need them in topological order, we produce it on demand by
   transforming the bitmap into an array and sorting it into topo
   Type of expression, used to know which member of the PRE_EXPR union
   is valid.  

Function Documentation

static void add_to_value ( )
   Add expression E to the expression set of value id V.  

Referenced by create_component_ref_by_pieces(), do_partial_partial_insertion(), and insert_aux().

static unsigned int alloc_expression_id ( )
   Allocate an expression id for EXPR.  
     Make sure we won't overflow. 
         vec::safe_grow_cleared allocates no headroom.  Avoid frequent
         re-allocations by using vec::reserve upfront.  There is no
         vec::quick_grow_cleared unfortunately.  
static pre_expr bitmap_find_leader ( bitmap_set_t  ,
unsigned  int 
static pre_expr bitmap_find_leader ( )
   Find the leader for a value (i.e., the name representing that
   value) in a given set, and return it.  Return NULL if no leader
   is found.  
         Rather than walk the entire bitmap of expressions, and see
         whether any of them has the value we are looking for, we look
         at the reverse mapping, which tells us the set of expressions
         that have a given value (IE value->expressions with that
         value) and see if any of those expressions are in our set.
         The number of expressions per value is usually significantly
         less than the number of expressions in the set.  In fact, for
         large testcases, doing it this way is roughly 5-10x faster
         than walking the bitmap.
         If this is somehow a significant lose for some cases, we can
         choose which set to walk based on which set is smaller.  

References bitmap_set_contains_value(), vn_ssa_aux::value_id, and VN_INFO().

static void bitmap_insert_into_set ( bitmap_set_t  ,
static void bitmap_insert_into_set ( )
   Insert an expression EXPR into a bitmapped set.  
static void bitmap_insert_into_set_1 ( bitmap_set_t  set,
pre_expr  expr,
unsigned int  val,
bool  allow_constants 
         We specifically expect this and only this function to be able to
         insert constants into a set.  

References bitmap_bit_p(), and expression_for_id().

static void bitmap_remove_from_set ( )
   Remove an expression EXPR from a bitmapped set.  
static void bitmap_set_and ( )
   Perform bitmapped set operation DEST &= ORIG.  

References bitmap_bit_p(), bitmap_empty_p(), and value_id_constant_p().

static bool bitmap_set_contains_expr ( )
static bool bitmap_set_contains_value ( bitmap_set_t  ,
unsigned  int 

Referenced by bitmap_find_leader().

static bool bitmap_set_contains_value ( )
   Return true if bitmapped set SET contains the value VALUE_ID.  
static void bitmap_set_copy ( bitmap_set_t  ,
static void bitmap_set_copy ( )
   Copy a bitmapped set ORIG, into bitmapped set DEST.  
static bool bitmap_set_equal ( )
   Return true if two bitmap sets are equal.  

References get_tree_code_name(), vn_reference_op_struct::op0, vn_reference_op_struct::opcode, and tcc_declaration.

static void bitmap_set_free ( )
   Free memory used up by SET.  
static bitmap_set_t bitmap_set_new ( )
   Create a new bitmap set and return it.  

References bitmap_clear_bit(), get_expr_value_id(), get_expression_id(), and value_id_constant_p().

static void bitmap_set_replace_value ( bitmap_set_t  set,
unsigned int  lookfor,
const pre_expr  expr 
   Replace an instance of value LOOKFOR with expression EXPR in SET.  
     The number of expressions having a given value is usually
     significantly less than the total number of expressions in SET.
     Thus, rather than check, for each expression in SET, whether it
     has the value LOOKFOR, we walk the reverse mapping that tells us
     what expressions have a given value, and see if any of those
     expressions are in our set.  For large testcases, this is about
     5-10x faster than walking the bitmap.  If this is somehow a
     significant lose for some cases, we can choose which set to walk
     based on the set size.  
static bitmap_set_t bitmap_set_subtract ( )
   Subtract all values and expressions contained in ORIG from DEST.  

References bitmap_clear_bit().

static void bitmap_set_subtract_values ( )
   Subtract all the values in bitmap set B from bitmap set A.  
static void bitmap_value_insert_into_set ( bitmap_set_t  ,
static void bitmap_value_insert_into_set ( )
   Insert EXPR into SET if EXPR's value is not already present in
     Constant values are always considered to be part of the set.  
     If the value membership changed, add the expression.  
static void bitmap_value_replace_in_set ( bitmap_set_t  ,
static void bitmap_value_replace_in_set ( )
   Replace an instance of EXPR's VALUE with EXPR in SET if it exists,
   and add it otherwise.  
static void clean ( )
   Clean the set of expressions that are no longer valid in SET.  This
   means expressions that are made up of values we have no leaders for
   in SET.  
static void clear_expression_ids ( )
   Free the expression id field in all of our expressions,
   and then destroy the expressions array.  
static void compute_antic ( )
   Compute ANTIC and partial ANTIC sets.  
     If any predecessor edges are abnormal, we punt, so antic_in is empty.
     We pre-build the map of blocks with incoming abnormal edges here.  
         While we are here, give empty ANTIC_IN sets to each block.  
     At the exit block we anticipate nothing.  
         ???  We need to clear our PHI translation cache here as the
         ANTIC sets shrink and we restrict valid translations to
         those having operands with leaders in ANTIC.  Same below
         for PA ANTIC computation.  
         Theoretically possible, but *highly* unlikely.  
             Theoretically possible, but *highly* unlikely.  

References build_int_cst(), get_addr_base_and_unit_offset(), HOST_WIDE_INT, and int_const_binop().

static bool compute_antic_aux ( )

Compute the ANTIC set for BLOCK.

If succs(BLOCK) > 1 then ANTIC_OUT[BLOCK] = intersection of ANTIC_IN[b] for all succ(BLOCK) else if succs(BLOCK) == 1 then ANTIC_OUT[BLOCK] = phi_translate (ANTIC_IN[succ(BLOCK)])


     If any edges from predecessors are abnormal, antic_in is empty,
     so do nothing.  
     If the block has no successors, ANTIC_OUT is empty.  
     If we have one successor, we could have some phi nodes to
     translate through.  
         We trade iterations of the dataflow equations for having to
         phi translate the maximal set, which is incredibly slow
         (since the maximal set often has 300+ members, even when you
         have a small number of blocks).
         Basically, we defer the computation of ANTIC for this block
         until we have processed it's successor, which will inevitably
         have a *much* smaller set of values to phi translate once
         clean has been run on it.
         The cost of doing this is that we technically perform more
         iterations, however, they are lower cost iterations.

         Timings for PRE on tramp3d-v4:
         without maximal set fix: 11 seconds
         with maximal set fix/without deferring: 26 seconds
         with maximal set fix/with deferring: 11 seconds
     If we have multiple successors, we take the intersection of all of
     them.  Note that in the case of loop exit phi nodes, we may have
     phis to translate through.  
         Of multiple successors we have to have visited one already.  
     Prune expressions that are clobbered in block and thus become
     invalid if translated from ANTIC_OUT to ANTIC_IN.  
     Generate ANTIC_OUT - TMP_GEN.  
     Start ANTIC_IN with EXP_GEN - TMP_GEN.  
     Then union in the ANTIC_OUT - TMP_GEN values,
     to get ANTIC_OUT U EXP_GEN - TMP_GEN 
static void compute_avail ( )
   Compute the AVAIL set for all basic blocks.

   This function performs value numbering of the statements in each basic
   block.  The AVAIL sets are built from information we glean while doing
   this value numbering, since the AVAIL sets contain only one entry per

     We pretend that default definitions are defined in the entry block.
     This includes function arguments and the static chain decl.  
     Allocate the worklist.  
     Seed the algorithm by putting the dominator children of the entry
     block on the worklist.  
     Loop until the worklist is empty.  
         Pick a block from the worklist.  
         Initially, the set of available values in BLOCK is that of
         its immediate dominator.  
         Generate values for PHI nodes.  
             We have no need for virtual phis, as they don't represent
             actual computations.  
         Now compute value numbers and populate value sets with all
         the expressions computed in BLOCK.  
             Cache whether the basic-block has any non-visible side-effect
             or control flow.
             If this isn't a call or it is the last stmt in the
             basic-block then the CFG represents things correctly.  
                 Non-looping const functions always return normally.
                 Otherwise the call might not return or have side-effects
                 that forbids hoisting possibly trapping expressions
                 before it.  
                   We can value number only calls to real functions.  
                   If the value of the call is not invalidated in
                   this block until it is computed, add the expression
                   to EXP_GEN.  
                         COND_EXPR and VEC_COND_EXPR are awkward in
                         that they contain an embedded complex expression.
                         Don't even try to shove those through PRE.  
                         If the NARY traps and there was a preceding
                         point in the block that might not return avoid
                         adding the nary to EXP_GEN.  
                         If the value of the reference is not invalidated in
                         this block until it is computed, add the expression
                         to EXP_GEN.  
         Put the dominator children of BLOCK on the worklist of blocks
         to compute available sets for.  
static bool compute_partial_antic_aux ( basic_block  block,
bool  block_has_abnormal_pred_edge 


If succs(BLOCK) > 1 then PA_OUT[BLOCK] = value wise union of PA_IN[b] + all ANTIC_IN not in ANTIC_OUT for all succ(BLOCK) else if succs(BLOCK) == 1 then PA_OUT[BLOCK] = phi_translate (PA_IN[succ(BLOCK)])

PA_IN[BLOCK] = dependent_clean(PA_OUT[BLOCK] - TMP_GEN[BLOCK]

     If any edges from predecessors are abnormal, antic_in is empty,
     so do nothing.  
     If there are too many partially anticipatable values in the
     block, phi_translate_set can take an exponential time: stop
     before the translation starts.  
     If the block has no successors, ANTIC_OUT is empty.  
     If we have one successor, we could have some phi nodes to
     translate through.  Note that we can't phi translate across DFS
     back edges in partial antic, because it uses a union operation on
     the successors.  For recurrences like IV's, we will end up
     generating a new value in the set on each go around (i + 3 (VH.1)
     VH.1 + 1 (VH.2), VH.2 + 1 (VH.3), etc), forever.  
     If we have multiple successors, we take the union of all of
     Prune expressions that are clobbered in block and thus become
     invalid if translated from PA_OUT to PA_IN.  
     PA_IN starts with PA_OUT - TMP_GEN.
     Then we subtract things from ANTIC_IN.  
     For partial antic, we want to put back in the phi results, since
     we will properly avoid making them partially antic over backedges.  
     PA_IN[block] = PA_IN[block] - ANTIC_IN[block] 

References bitmap_set_bit(), edge_def::flags, and basic_block_def::index.

static tree create_component_ref_by_pieces ( basic_block  block,
vn_reference_t  ref,
gimple_seq stmts 
   For COMPONENT_REF's and ARRAY_REF's, we can't have any intermediates for the
   COMPONENT_REF or MEM_REF or ARRAY_REF portion, because we'd end up with
   trying to rename aggregates into ssa form directly, which is a no no.

   Thus, this routine doesn't create temporaries, it just builds a
   single access expression for the array, calling
   find_or_generate_expression to build the innermost pieces.

   This function is a subroutine of create_expression_by_pieces, and
   should not be called on it's own unless you really know what you
   are doing.  

References add_to_value(), bitmap_set_bit(), bitmap_value_replace_in_set(), get_next_value_id(), get_or_alloc_expr_for_name(), vn_ssa_aux::valnum, vn_ssa_aux::value_id, VN_INFO(), and VN_INFO_GET().

static tree create_component_ref_by_pieces_1 ( basic_block  block,
vn_reference_t  ref,
unsigned int *  operand,
gimple_seq stmts 
   The actual worker for create_component_ref_by_pieces.  
         For array ref vn_reference_op's, operand 1 of the array ref
         is op0 of the reference op and operand 3 of the array ref is
               Drop zero minimum index if redundant.  
               We can't always put a size in units of the element alignment
               here as the element alignment may be not visible.  See
               PR43783.  Simply drop the element size for constant
           op1 should be a FIELD_DECL, which are represented by themselves.  

References find_or_generate_expression().

static tree create_expression_by_pieces ( basic_block  block,
pre_expr  expr,
gimple_seq stmts,
tree  type 
   Create an expression in pieces, so that we can handle very complex
   expressions that may be ANTIC, but not necessary GIMPLE.
   BLOCK is the basic block the expression will be inserted into,
   EXPR is the expression to insert (in value form)
   STMTS is a statement list to append the necessary insertions into.

   This function will die if we hit some value that shouldn't be
   ANTIC but is (IE there is no leader for it, or its components).
   The function returns NULL_TREE in case a different antic expression
   has to be inserted first.
   This function may also generate expressions that are themselves
   partially or fully redundant.  Those that are will be either made
   fully redundant during the next iteration of insert (for partially
   redundant ones), or eliminated by eliminate (for fully redundant
         We may hit the NAME/CONSTANT case if we have to convert types
         that value numbering saw through.  
               Ensure genop[] is properly typed for POINTER_PLUS_EXPR.  It
               may have conversions stripped.  
     Force the generated expression to be a sequence of GIMPLE
     We have to call unshare_expr because force_gimple_operand may
     modify the tree we pass to it.  
     If we have any intermediate expressions to the value sets, add them
     to the value sets and chain them in the instruction stream.  
     Fold the last statement.  
     Add a value number to the temporary.
     The value may already exist in either NEW_SETS, or AVAIL_OUT, because
     we are creating the expression by pieces, and this particular piece of
     the expression may have been represented.  There is no harm in replacing

References flow_bb_inside_loop_p(), gimple_bb(), basic_block_def::loop_father, vn_reference_op_struct::op0, vn_reference_op_struct::opcode, and simple_iv().

void debug_bitmap_set ( bitmap_set_t  )
DEBUG_FUNCTION void debug_bitmap_set ( )
void debug_bitmap_sets_for ( basic_block  )
DEBUG_FUNCTION void debug_bitmap_sets_for ( )
void debug_pre_expr ( pre_expr  )
DEBUG_FUNCTION void debug_pre_expr ( )
   Like print_pre_expr but always prints to stderr.  
DEBUG_FUNCTION void debug_value_expressions ( )
static bool defer_or_phi_translate_block ( bitmap_set_t  dest,
bitmap_set_t  source,
basic_block  block,
basic_block  phiblock 
   Decide whether to defer a block for a later iteration, or PHI
   translate SOURCE to DEST using phis in PHIBLOCK.  Return false if we
   should defer the block, and true if we processed it.  
static void dependent_clean ( )
   Clean the set of expressions that are no longer valid in SET1 or
   SET2.  This means expressions that are made up of values we have no
   leaders for in SET1 or SET2.  This version is used for partial
   anticipation, which means it is not valid in either ANTIC_IN or

References single_succ().

static bool do_partial_partial_insertion ( )
   Perform insertion for partially anticipatable expressions.  There
   is only one case we will perform insertion for these.  This case is
   if the expression is partially anticipatable, and fully available.
   In this case, we know that putting it earlier will enable us to
   remove the later computation.  
                 We should never run insertion for the exit block
                 and so not come across fake pred edges.  
                 eprime will generally only be NULL if the
                 value of the expression, translated
                 through the PHI for this predecessor, is
                 undefined.  If that is the case, we can't
                 make the expression fully redundant,
                 because its value is undefined along a
                 predecessor path.  We can thus break out
                 early because it doesn't matter what the
                 rest of the results are.  
             If we can insert it, it's not the same value
             already existing along every predecessor, and
             it's defined by some predecessor, it is
             partially redundant.  
                 Insert only if we can remove a later expression on a path
                 that we want to optimize for speed.
                 The phi node that we will be inserting in BLOCK is not free,
                 and inserting it for the sake of !optimize_for_speed successor
                 may cause regressions on the speed path.  

References add_to_value(), bitmap_insert_into_set(), bitmap_set_copy(), bitmap_value_insert_into_set(), CDI_DOMINATORS, dom, dump_file, dump_flags, first_dom_son(), get_expr_value_id(), get_immediate_dominator(), get_or_alloc_expr_for_name(), gimple_call_flags(), gimple_has_side_effects(), gimple_phi_result(), gsi_end_p(), gsi_next(), gsi_start_bb(), gsi_start_phis(), gsi_stmt(), has_zero_uses(), is_gimple_call(), is_gimple_debug(), next_dom_son(), print_bitmap_set(), ssa_undefined_value_p(), stmt_could_throw_p(), stmt_ends_bb_p(), virtual_operand_p(), and worklist.

static unsigned int do_pre ( )
   Gate and execute functions for PRE.  
     This has to happen before SCCVN runs because
     loop_optimizer_init may create new phis, etc.  
     Collect and value number expressions computed in each basic block.  
     Insert can get quite slow on an incredibly large number of basic
     blocks due to some quadratic behavior.  Until this behavior is
     fixed, don't run it when he have an incredibly large number of
     bb's.  If we aren't going to run insert, there is no point in
     computing ANTIC, either, even though it's plenty fast.  
     Make sure to remove fake edges before committing our inserts.
     This makes sure we don't end up with extra critical edges that
     we would need to split.  
     Remove all the redundant expressions.  
     TODO: tail_merge_optimize may merge all predecessors of a block, in which
     case we can merge the block with the remaining predecessor of the block.
     It should either:
     - call merge_blocks after each tail merge iteration
     - call merge_blocks after all tail merge iterations
     - mark TODO_cleanup_cfg when necessary
     - share the cfg cleanup with fini_pre.  
     Tail merging invalidates the virtual SSA web, together with
     cfg-cleanup opportunities exposed by PRE this will wreck the
     SSA updating machinery.  So make sure to run update-ssa
     manually, before eventually scheduling cfg-cleanup as part of
     the todo.  

Referenced by mark_operand_necessary().

static bool do_regular_insertion ( )

Perform insertion of partially redundant values. For BLOCK, do the following:

  1. Propagate the NEW_SETS of the dominator into the current block. If the block has multiple predecessors, 2a. Iterate over the ANTIC expressions for the block to see if any of them are partially redundant. 2b. If so, insert them into the necessary predecessors to make the expression fully redundant. 2c. Insert a new PHI merging the values of the predecessors. 2d. Insert the new PHI, and the new expressions, into the NEW_SETS set.
  2. Recursively call ourselves on the dominator children of BLOCK.

Steps 1, 2a, and 3 are done by insert_aux. 2b, 2c and 2d are done by do_regular_insertion and do_partial_insertion.

                 We should never run insertion for the exit block
                 and so not come across fake pred edges.  
                 eprime will generally only be NULL if the
                 value of the expression, translated
                 through the PHI for this predecessor, is
                 undefined.  If that is the case, we can't
                 make the expression fully redundant,
                 because its value is undefined along a
                 predecessor path.  We can thus break out
                 early because it doesn't matter what the
                 rest of the results are.  
                     We want to perform insertions to remove a redundancy on
                     a path in the CFG we want to optimize for speed.  
             If we can insert it, it's not the same value
             already existing along every predecessor, and
             it's defined by some predecessor, it is
             partially redundant.  
             If all edges produce the same value and that value is
             an invariant, then the PHI has the same value on all
             edges.  Note this.  
static unsigned int eliminate ( )
   Eliminate fully redundant computations.  
     We cannot remove stmts during BB walk, especially not release SSA
     names there as this confuses the VN machinery.  The stmts ending
     up in el_to_remove are either stores or simple copies.  
         If there is a single use only, propagate the equivalency
         instead of keeping the copy.  
         If this is a store or a now unused copy, remove it.  
     We cannot update call statements with virtual operands during
     SSA walk.  This might remove them which in turn makes our
     VN lattice invalid.  
static tree eliminate_avail ( )
   Return a leader for OP that is available at the current point of the
   eliminate domwalk.  

References dump_file, dump_flags, is_gimple_call(), print_generic_expr(), print_gimple_expr(), and stmt_can_make_abnormal_goto().

static tree eliminate_insert ( )
   Insert the expression recorded by SCCVN for VAL at *GSI.  Returns
   the leader for the expression if insertion was successful.  
static void eliminate_push_avail ( )
   At the current point of the eliminate domwalk make OP available.  
static unsigned int execute_fre ( )
   Gate and execute functions for FRE.  
     Remove all the redundant expressions.  
static pre_expr expression_for_id ( )
   Return the expression that has expression id ID 

References pre_expr_d::id, pre_expr_d::kind, lookup_expression_id(), and NAME.

Referenced by bitmap_insert_into_set_1(), and debug_bitmap_set().

static pre_expr find_leader_in_sets ( )
   Like bitmap_find_leader, but checks for the value existing in SET1 *or*
   SET2.  This is used to avoid making a set consisting of the union
   of PA_IN and ANTIC_IN during insert.  

Referenced by get_expr_type(), and phi_translate_1().

static tree find_or_generate_expression ( basic_block  ,
tree  ,
static tree find_or_generate_expression ( )
   Find a simple leader for an expression, or generate one using
   create_expression_by_pieces from a NARY expression for the value.
   BLOCK is the basic_block we are looking for leaders in.
   OP is the tree expression to find a leader for or generate.
   Returns the leader or NULL_TREE on failure.  
     It must be a complex expression, so generate it recursively.  Note
     that this is only necessary to handle gcc.dg/tree-ssa/ssa-pre28.c
     where the insert algorithm fails to insert a required expression.  
         We cannot insert random REFERENCE expressions at arbitrary
         places.  We can insert NARYs which eventually re-materializes
         its operand values.  
static unsigned fini_eliminate ( )
   Perform CFG cleanups made necessary by elimination.  
static void fini_pre ( )
   Deallocate data structures used by PRE.  
static pre_expr fully_constant_expression ( )
   Return the folded version of T if T, when folded, is a gimple
   min_invariant.  Otherwise, return T.  
                 We have to go from trees to pre exprs to value ids to
                 We might have simplified the expression to a
                 SSA_NAME for example from x_1 * 1.  But we cannot
                 insert a PHI for x_1 unconditionally as x_1 might
                 not be available readily.  
                 We have to go from trees to pre exprs to value ids to
static bool gate_fre ( )
static bool gate_pre ( )

Referenced by mark_operand_necessary().

static tree get_constant_for_value_id ( )
   Given a value id V, find the actual tree representing the constant
   value if there is one, and return it. Return NULL if we can't find
   a constant.  

Referenced by get_or_alloc_expr_for(), and get_or_alloc_expr_for_constant().

static tree get_expr_type ( )
static unsigned int get_expr_value_id ( )
   Return the value id for a PRE expression EXPR.  
     ???  We cannot assert that expr has a value-id (it can be 0), because
     we assign value-ids only to expressions that have a result
     in set_hashtable_value_ids.  
static unsigned int get_expression_id ( )
   Return the expression id for tree EXPR.  

References hash_table< Descriptor, Allocator >::find_slot(), and pre_expr_d::id.

Referenced by bitmap_set_new(), and phi_translate().

static pre_expr get_or_alloc_expr_for ( )
   Get or allocate a pre_expr for a piece of GIMPLE, and return it.
   Currently only supports constants and SSA_NAMES.  
         More complex expressions can result from SCCVN expression
         simplification that inserts values for them.  As they all
         do not have VOPs the get handled by the nary ops struct.  

References get_constant_for_value_id(), get_expr_value_id(), get_or_alloc_expr_for_constant(), is_gimple_min_invariant(), vn_nary_op_s::op, and vn_nary_op_s::type.

Referenced by get_or_alloc_expr_for_constant().

static pre_expr get_or_alloc_expr_for_constant ( )
   Given a CONSTANT, allocate a new CONSTANT type PRE_EXPR to
   represent it.  

References CONSTANT, get_constant_for_value_id(), get_expr_value_id(), get_or_alloc_expr_for(), is_gimple_min_invariant(), pre_expr_d::kind, NARY, vn_nary_op_s::op, tcc_binary, and tcc_comparison.

Referenced by get_or_alloc_expr_for().

static pre_expr get_or_alloc_expr_for_name ( )
   Given an SSA_NAME NAME, get or create a pre_expr to represent it.  

References bitmap_set::expressions, and bitmap_set::values.

Referenced by create_component_ref_by_pieces(), and do_partial_partial_insertion().

static unsigned int get_or_alloc_expression_id ( )
   Return the existing expression id for EXPR, or create one if one
   does not exist yet.  

Referenced by bitmap_set_contains_expr(), and insert_aux().

static tree get_representative_for ( )
   Get a representative SSA_NAME for a given expression.
   Since all of our sub-expressions are treated as values, we require
   them to be SSA_NAME's for simplicity.
   Prior versions of GVNPRE used to use "value handles" here, so that
   an expression would be VH.11 + VH.10 instead of d_3 + e_6.  In
   either case, the operands are really values (IE we do not expect
   them to be usable without finding leaders).  
           Go through all of the expressions representing this value
           and pick out an SSA_NAME.  
     If we reached here we couldn't find an SSA_NAME.  This can
     happen when we've discovered a value that has never appeared in
     the program as set to an SSA_NAME, as the result of phi translation.
     Create one here.
     ???  We should be able to re-use this when we insert the statement
     to compute it.  
     ???  For now mark this SSA name for release by SCCVN.  

Referenced by get_expr_type(), and phi_translate_1().

static bool inhibit_phi_insertion ( )
   Returns true if we want to inhibit the insertions of PHI nodes
   for the given EXPR for basic block BB (a member of a loop).
   We want to do this, when we fear that the induction variable we
   create might inhibit vectorization.  
     If we aren't going to vectorize we don't inhibit anything.  
     Otherwise we inhibit the insertion when the address of the
     memory reference is a simple induction variable.  In other
     cases the vectorizer won't do anything anyway (either it's
     loop invariant or a complicated expression).  
             Calls are not a problem.  
               Default defs are loop invariant.  
               Defined outside this loop, also loop invariant.  
               If it's a simple induction variable inhibit insertion,
               the vectorizer might be interested in this one.  
               No simple IV, vectorizer can't do anything, hence no
               reason to inhibit the transformation for this operand.  

References bitmap_set_bit(), gimple_get_lhs(), gimple_set_plf(), gsi_end_p(), gsi_insert_seq_on_edge(), gsi_next(), and gsi_stmt().

static void init_pre ( )
   Initialize data structures used by PRE.  
static void insert ( )
   Perform insertion of partially redundant values.  
         Clear the NEW sets before the next iteration.  We have already
         fully propagated its contents.  
static bool insert_aux ( )
                 Note that we need to value_replace both NEW_SETS, and
                 AVAIL_OUT. For both the case of NEW_SETS, the value may be
                 represented by some non-simple expression here that we want
                 to replace it with.  

References add_to_value(), bitmap_value_insert_into_set(), copy_reference_ops_from_call(), get_expr_value_id(), get_or_alloc_expression_id(), gimple_call_internal_p(), gimple_expr_type(), gimple_vuse(), pre_expr_d::id, pre_expr_d::kind, pool_alloc(), REFERENCE, VN_NOWALK, vn_reference_lookup_pieces(), and vNULL.

static bool insert_into_preds_of_block ( basic_block  block,
unsigned int  exprnum,
vec< pre_expr avail 
   Insert the to-be-made-available values of expression EXPRNUM for each
   predecessor, stored in AVAIL, into the predecessors of BLOCK, and
   merge the result with a phi node, given the same value number as
   NODE.  Return true if we have inserted new stuff.  
     Make sure we aren't creating an induction variable.  
         Induction variables only have one edge inside the loop.  
     Make the necessary insertions.  
                 We cannot insert a PHI node if we failed to insert
                 on one edge.  
             Constants may not have the right type, fold_convert
             should give us back a constant with the right type.  
             We may have to do a conversion because our value
             numbering can look through types in certain cases, but
             our IL requires all operands of a phi node have the same
     If we didn't want a phi node, and we made insertions, we still have
     inserted new stuff, and thus return true.  If we didn't want a phi node,
     and didn't make insertions, we haven't added anything new, so return
     Now build a phi for the new variable.  
     The value should *not* exist in PHI_GEN, or else we wouldn't be doing
     this insertion, since we test for the existence of this value in PHI_GEN
     before proceeding with the partial redundancy checks in insert_aux.

     The value may exist in AVAIL_OUT, in particular, it could be represented
     by the expression we are trying to eliminate, in which case we want the
     replacement to occur.  If it's not existing in AVAIL_OUT, we want it
     inserted there.

     Similarly, to the PHI_GEN case, the value should not exist in NEW_SETS of
     this block, because if it did, it would have existed in our dominator's
     AVAIL_OUT, and would have been skipped due to the full redundancy check.
static unsigned int lookup_expression_id ( )

Referenced by expression_for_id().

gimple_opt_pass* make_pass_fre ( )
gimple_opt_pass* make_pass_pre ( )
static gimple mark_operand_necessary ( )
   Borrow a bit of tree-ssa-dce.c for the moment.
   XXX: In 4.1, we should be able to just run a DCE pass after PRE, though
   this may be a bit faster, and we may want critical edges kept split.  
   If OP's defining statement has not already been determined to be necessary,
   mark that statement necessary. Return the stmt, if it is newly

References do_pre(), opt_pass::execute(), opt_pass::gate(), gate_pre(), and gimple_opt_pass::gimple_opt_pass().

static bool op_valid_in_sets ( )
   Determine if OP is valid in SET1 U SET2, which it is when the union
   contains its value-id.  
static bool phi_trans_add ( )
   Add the tuple mapping from {expression E, basic block PRED} to
   the phi translation table and return whether it pre-existed.  
static pre_expr phi_translate ( pre_expr  expr,
bitmap_set_t  set1,
bitmap_set_t  set2,
basic_block  pred,
basic_block  phiblock 
   Wrapper around phi_translate_1 providing caching functionality.  
     Constants contain no values that need translation.  
     Don't add translations of NAMEs as those are cheap to translate.  
         Store NULL for the value we want to return in the case of
           Remove failed translations again, they cause insert
           iteration to not pick up new opportunities reliably.  

References ao_ref_s::base, bitmap_bit_p(), get_expression_id(), gimple_vdef(), gimple_vuse(), gsi_end_p(), gsi_next(), gsi_start_bb(), and gsi_stmt().

Referenced by get_expr_type(), and phi_translate_1().

static pre_expr phi_translate_1 ( pre_expr  expr,
bitmap_set_t  set1,
bitmap_set_t  set2,
basic_block  pred,
basic_block  phiblock 
   Translate EXPR using phis in PHIBLOCK, so that it has the values of
   the phis in PRED.  Return NULL if we can't find a leader for each part
   of the translated expression.  
                       We can't possibly insert these.  
               We may have changed from an SSA_NAME to a constant 
               If it transforms a non-constant ARRAY_REF into a constant
               one, adjust the constant offset.  
               If it transforms from an SSA_NAME to an address, fold with
               a preceding indirect reference.  
               We can always insert constants, so if we have a partial
               redundant constant load of another type try to translate it
               to a constant of appropriate type.  
               If we'd have to convert things we would need to validate
               if we can insert the translated expression.  So fail
               here for now - we cannot insert an alias with a different
               type in the VN tables either, as that would assert.  
           If the SSA name is defined by a PHI node in this block,
           translate it.  
               Handle constant. 
           Otherwise return it unchanged - it will get cleaned if its
           value is not available in PREDs AVAIL_OUT set of expressions.  

References find_leader_in_sets(), get_representative_for(), is_gimple_min_invariant(), phi_translate(), vn_ssa_aux::value_id, and VN_INFO().

static void phi_translate_set ( bitmap_set_t  dest,
bitmap_set_t  set,
basic_block  pred,
basic_block  phiblock 
   For each expression in SET, translate the values through phi nodes
   in PHIBLOCK using edge PHIBLOCK->PRED, and store the resulting
   expressions in DEST.  
         We might end up with multiple expressions from SET being
         translated to the same value.  In this case we do not want
         to retain the NARY or REFERENCE expression but prefer a NAME
         which would be the leader.  

Referenced by valid_in_sets().

static void print_bitmap_set ( FILE *  outfile,
bitmap_set_t  set,
const char *  setname,
int  blockindex 
   Print out SET to OUTFILE.  

Referenced by do_partial_partial_insertion().

static void print_pre_expr ( )
   Print out EXPR to outfile.  
static void print_value_expressions ( )
   Print out the expressions that have VAL to OUTFILE.  
static void prune_clobbered_mems ( )
   Clean the set of expressions that are no longer valid in SET because
   they are clobbered in BLOCK or because they trap and may not be executed.  
             If the NARY may trap make sure the block does not contain
             a possible exit point.
             ???  This is overly conservative if we translate AVAIL_OUT
             as the available expression might be after the exit point.  

References edge_def::dest.

static void remove_dead_inserted_code ( )
   Because we don't follow exactly the standard PRE algorithm, and decide not
   to insert PHI nodes sometimes, and because value numbering of casts isn't
   perfect, we sometimes end up inserting dead code.   This simple DCE-like
   pass removes any insertions we made that weren't actually used.  
         PHI nodes are somewhat special in that each PHI alternative has
         data and control dependencies.  All the statements feeding the
         PHI node's arguments are always necessary. 
             Propagate through the operands.  Examine all the USE, VUSE and
             VDEF operands in this statement.  Mark all the statements
             which feed this statement's uses as necessary.  
             The operands of VDEF expressions are also needed as they
             represent potential definitions that may reach this
             statement (VDEF operands allow us to follow def-def
static tree sccvn_valnum_from_value_id ( )
   Return a SCCVN valnum (SSA name or constant) for the PRE value-id VAL.  

References bitmap_clear().

static vec<pre_expr> sorted_array_from_bitmap_set ( )
   Generate an topological-ordered array of bitmap set SET.  
     Pre-allocate roughly enough space for the array.  
         The number of expressions having a given value is usually
         relatively small.  Thus, rather than making a vector of all
         the expressions and sorting it by value-id, we walk the values
         and check in the reverse mapping that tells us what expressions
         have a given value, to filter those in our set.  As a result,
         the expressions are inserted in value-id order, which means
         topological order.

         If this is somehow a significant lose for some cases, we can
         choose which set to walk based on the set size.  
static tree translate_vuse_through_block ( vec< vn_reference_op_s operands,
alias_set_type  set,
tree  type,
tree  vuse,
basic_block  phiblock,
basic_block  block,
bool *  same_valid 
   Translate the VUSE backwards through phi nodes in PHIBLOCK, so that
   it has the value it would have in BLOCK.  Set *SAME_VALID to true
   in case the new vuse doesn't change the value id of the OPERANDS.  
     Use the alias-oracle to find either the PHI node in this block,
     the first VUSE used in this block that is equivalent to vuse or
     the first VUSE which definition in this block kills the value.  
             Try to find a vuse that dominates this phi node by skipping
             non-clobbering statements.  
             If we didn't find any, the value ID can't stay the same,
             but return the translated vuse.  
         ??? We would like to return vuse here as this is the canonical
         upmost vdef that this reference is associated with.  But during
         insertion of the references into the hash tables we only ever
         directly insert with their direct gimple_vuse, hence returning
         something else would make us not find the other expression.  


static bool valid_in_sets ( bitmap_set_t  set1,
bitmap_set_t  set2,
pre_expr  expr,
basic_block  block 
   Determine if the expression EXPR is valid in SET1 U SET2.
   This means that we have a leader for each part of the expression
   (if it consists of values), or the expression is an SSA_NAME.
   For loads/calls, we also see if the vuse is killed in this block.  

References bitmap_set_bit(), basic_block_def::index, and phi_translate_set().

static bool value_dies_in_block_x ( )
   Determine if EXPR, a memory expression, is ANTIC_IN at the top of
   BLOCK by seeing if it is not killed in the block.  Note that we are
   only determining whether there is a store that kills it.  Because
   of the order in which clean iterates over values, we are guaranteed
   that altered operands will have caused us to be eliminated from the
   ANTIC_IN set already.  
     Lookup a previously calculated result.  
     A memory expression {e, VUSE} dies in the block if there is a
     statement that may clobber e.  If, starting statement walk from the
     top of the basic block, a statement uses VUSE there can be no kill
     inbetween that use and the original statement that loaded {e, VUSE},
     so we can stop walking.  
         Not a memory statement.  
         Not a may-def.  
             A load with the same VUSE, we're done.  
         Init ref only if we really need it.  
         If the statement may clobber expr, it dies.  
     Remember the result.  

Variable Documentation

alloc_pool bitmap_set_pool
   We can add and remove elements and entries to and from sets
   and hash tables, so we use alloc pools for them.  
sbitmap changed_blocks
   List of blocks that may have changed during ANTIC computation and
   thus need to be iterated over.  
bool do_partial_partial
vec<tree> el_avail
vec<tree> el_avail_stack
vec<gimple> el_to_remove
   Local state for the eliminate domwalk.  
vec<gimple> el_to_update
unsigned int el_todo
hash_table<pre_expr_d> expression_to_id
vec<pre_expr> expressions
   Mapping from expression to id number we can use in bitmap sets.  
bitmap_obstack grand_bitmap_obstack
sbitmap has_abnormal_preds
bitmap inserted_exprs
   Inserted expressions are placed onto this worklist, which is used
   for performing quick dead code elimination of insertions we made
   that didn't turn out to be necessary.   
vec<unsigned> name_to_id
bitmap need_ab_cleanup
   Set of blocks with statements that have had their AB properties changed.  
bitmap need_eh_cleanup
   Set of blocks with statements that have had their EH properties changed.  
unsigned int next_expression_id
   Next global expression id number.  
hash_table<expr_pred_trans_d> phi_translate_table
   The phi_translate_table caches phi translations for a given
   expression and predecessor.  
int* postorder
   Basic block list in postorder.  
int postorder_num

Referenced by dom_walker::walk().

alloc_pool pre_expr_pool
struct { ... } pre_stats
   This structure is used to keep track of statistics on what
   optimization PRE was able to perform.  
vec<bitmap> value_expressions
   Mapping from value id to expressions with that value_id.