GCC Middle and Back End API Reference
cselib.c File Reference
#include "tm_p.h"
#include "regs.h"
Include dependency graph for cselib.c:

Data Structures

struct  elt_list
struct  expand_value_data
struct  cselib_hasher
struct  cselib_record_autoinc_data


static void promote_debug_loc (struct elt_loc_list *l)
static struct elt_listnew_elt_list (struct elt_list *, cselib_val *)
static void new_elt_loc_list (cselib_val *, rtx)
static void unchain_one_value (cselib_val *)
static void unchain_one_elt_list (struct elt_list **)
static void unchain_one_elt_loc_list (struct elt_loc_list **)
static void remove_useless_values (void)
static int rtx_equal_for_cselib_1 (rtx, rtx, enum machine_mode)
static unsigned int cselib_hash_rtx (rtx, int, enum machine_mode)
static cselib_valnew_cselib_val (unsigned int, enum machine_mode, rtx)
static void add_mem_for_addr (cselib_val *, cselib_val *, rtx)
static cselib_valcselib_lookup_mem (rtx, int)
static void cselib_invalidate_regno (unsigned int, enum machine_mode)
static void cselib_invalidate_mem (rtx)
static void cselib_record_set (rtx, cselib_val *, cselib_val *)
static void cselib_record_sets (rtx)
static rtx cselib_expand_value_rtx_1 (rtx, struct expand_value_data *, int)
static struct elt_listnew_elt_list ()
static void new_elt_loc_list ()
static void promote_debug_loc ()
static void unchain_one_elt_list ()
static void unchain_one_elt_loc_list ()
static void unchain_one_value ()
void cselib_clear_table ()
static bool invariant_or_equiv_p ()
int preserve_constants_and_equivs ()
void cselib_reset_table ()
unsigned int cselib_get_next_uid ()
static cselib_val ** cselib_find_slot (rtx x, hashval_t hash, enum insert_option insert, enum machine_mode memmode)
int references_value_p ()
int discard_useless_locs ()
int discard_useless_values ()
void cselib_preserve_value ()
bool cselib_preserved_value_p ()
void cselib_preserve_cfa_base_value ()
void cselib_preserve_only_values ()
void cselib_set_value_sp_based ()
bool cselib_sp_based_value_p ()
enum machine_mode cselib_reg_set_mode ()
int rtx_equal_for_cselib_p ()
static rtx autoinc_split ()
static int rtx_equal_for_cselib_1 ()
static rtx wrap_constant ()
static unsigned int cselib_hash_rtx ()
static cselib_valnew_cselib_val ()
static void add_mem_for_addr ()
static cselib_valcselib_lookup_mem ()
static rtx expand_loc (struct elt_loc_list *p, struct expand_value_data *evd, int max_depth)
rtx cselib_expand_value_rtx ()
rtx cselib_expand_value_rtx_cb (rtx orig, bitmap regs_active, int max_depth, cselib_expand_callback cb, void *data)
bool cselib_dummy_expand_value_rtx_cb (rtx orig, bitmap regs_active, int max_depth, cselib_expand_callback cb, void *data)
rtx cselib_subst_to_values ()
rtx cselib_subst_to_values_from_insn ()
static cselib_valcselib_lookup_1 (rtx x, enum machine_mode mode, int create, enum machine_mode memmode)
cselib_valcselib_lookup_from_insn (rtx x, enum machine_mode mode, int create, enum machine_mode memmode, rtx insn)
cselib_valcselib_lookup (rtx x, enum machine_mode mode, int create, enum machine_mode memmode)
static void cselib_invalidate_regno ()
static void cselib_invalidate_mem ()
void cselib_invalidate_rtx ()
static void cselib_invalidate_rtx_note_stores (rtx dest, const_rtx ignore, void *data)
static void cselib_record_set ()
void cselib_add_permanent_equiv ()
bool cselib_have_permanent_equivalences ()
static int cselib_record_autoinc_cb (rtx mem, rtx op, rtx dest, rtx src, rtx srcoff, void *arg)
static void cselib_record_sets ()
bool fp_setter_insn ()
void cselib_process_insn ()
void cselib_init ()
void cselib_finish ()
int dump_cselib_val ()
void dump_cselib_table ()


static enum machine_mode find_slot_memmode
static bool cselib_record_memory
static bool cselib_preserve_constants
static bool cselib_any_perm_equivs
static hash_table< cselib_hashercselib_hash_table
static rtx cselib_current_insn
static unsigned int next_uid
static unsigned int cselib_nregs
static int n_useless_values
static int n_useless_debug_values
static int n_debug_values
static struct elt_list ** reg_values
static unsigned int reg_values_size
static unsigned int max_value_regs
static unsigned int * used_regs
static unsigned int n_used_regs
static rtx callmem
static int values_became_useless
static cselib_val dummy_val
static cselib_valcfa_base_preserved_val
static unsigned int cfa_base_preserved_regno = INVALID_REGNUM
static cselib_valfirst_containing_mem = &dummy_val
static alloc_pool elt_loc_list_pool
static alloc_pool elt_list_pool
static alloc_pool cselib_val_pool
static alloc_pool value_pool
void(* cselib_discard_hook )(cselib_val *)
void(* cselib_record_sets_hook )(rtx insn, struct cselib_set *sets, int n_sets)

Function Documentation

static void add_mem_for_addr ( cselib_val ,
cselib_val ,
static void add_mem_for_addr ( )
   ADDR_ELT is a value that is used as address.  MEM_ELT is the value that
   contains the data at this address.  X is a MEM that represents the
   value.  Update the two value structures to represent this situation.  
     Avoid duplicates.  

References bitmap_bit_p(), cfa_base_preserved_regno, dump_file, dump_flags, elt_loc_list::loc, and expand_value_data::regs_active.

static rtx autoinc_split ( )
   If x is a PLUS or an autoinc operation, expand the operation,
   storing the offset, if any, in *OFF.  
void cselib_add_permanent_equiv ( )
   Make ELT and X's VALUE equivalent to each other at INSN.  
void cselib_clear_table ( void  )
   Remove all entries from the hash table.  Also used during

Referenced by fp_setter_insn().

bool cselib_dummy_expand_value_rtx_cb ( rtx  orig,
bitmap  regs_active,
int  max_depth,
cselib_expand_callback  cb,
void *  data 
   Similar to cselib_expand_value_rtx_cb, but no rtxs are actually copied
   or simplified.  Useful to find out whether cselib_expand_value_rtx_cb
   would return NULL or non-NULL, without allocating new rtx.  

References expand_value_data::callback, expand_value_data::callback_arg, and expand_value_data::regs_active.

rtx cselib_expand_value_rtx ( )
   Forward substitute and expand an expression out to its roots.
   This is the opposite of common subexpression.  Because local value
   numbering is such a weak optimization, the expanded expression is
   pretty much unique (not from a pointer equals point of view but
   from a tree shape point of view.

   This function returns NULL if the expansion fails.  The expansion
   will fail if there is no value number for one of the operands or if
   one of the operands has been overwritten between the current insn
   and the beginning of the basic block.  For instance x has no
   expansion in:

   r1 <- r1 + 3
   x <- r1 + 8

   REGS_ACTIVE is a scratch bitmap that should be clear when passing in.
   It is clear on return.  
static rtx cselib_expand_value_rtx_1 ( rtx  orig,
struct expand_value_data evd,
int  max_depth 
   Internal implementation of cselib_expand_value_rtx and
     For the context of dse, if we end up expand into a huge tree, we
     will not have a useful address, so we might as well just give up
                 The only thing that we are not willing to do (this
                 is requirement of dse and if others potential uses
                 need this function we should add a parm to control
                 it) is that we will not substitute the

                 These expansions confuses the code that notices that
                 stores into the frame go dead at the end of the
                 function and that the frame is not effected by calls
                 to subroutines.  If you allow the
                 STACK_POINTER_REGNUM substitution, then dse will
                 think that parameter pushing also goes dead which is
                 wrong.  If you allow the FRAME_POINTER or the
                 HARD_FRAME_POINTER then you lose the opportunity to
                 make the frame assumptions.  
         SCRATCH must be shared because they represent distinct values.  
     Copy the various flags, fields, and other information.  We assume
     that all fields need copying, and then clear the fields that should
     not be copied.  That is the sensible default behavior, and forces
     us to explicitly document why we are *not* copying a flag.  
           These are left unchanged.  
     If an operand has been simplified into CONST_INT, which doesn't
     have a mode and the mode isn't derivable from whole rtx's mode,
     try simplify_*_operation first with mode from original's operand
     and as a fallback wrap CONST_INT into gen_rtx_CONST.  
         These expressions can derive operand modes from the whole rtx's mode.  

Referenced by expand_loc().

rtx cselib_expand_value_rtx_cb ( rtx  orig,
bitmap  regs_active,
int  max_depth,
cselib_expand_callback  cb,
void *  data 
   Same as cselib_expand_value_rtx, but using a callback to try to
   resolve some expressions.  The CB function should return ORIG if it
   can't or does not want to deal with a certain RTX.  Any other
   return value, including NULL, will be used as the expansion for
   VALUE, without any further changes.  

Referenced by loc_exp_insert_dep().

static cselib_val** cselib_find_slot ( rtx  x,
hashval_t  hash,
enum insert_option  insert,
enum machine_mode  memmode 
   Search for X, whose hashcode is HASH, in CSELIB_HASH_TABLE,
   INSERTing if requested.  When X is part of the address of a MEM,
   MEMMODE should specify the mode of the MEM.  While searching the
   table, MEMMODE is held in FIND_SLOT_MEMMODE, so that autoinc RTXs
   in X can be resolved.  

References elt_loc_list::next, references_value_p(), and unchain_one_elt_loc_list().

void cselib_finish ( void  )
   Called when the current user is done with cselib.  

Referenced by chain_to_prev_insn_p().

unsigned int cselib_get_next_uid ( void  )
   Return the number of the next value that will be generated.  

Referenced by emit_notes_for_changes().

static unsigned int cselib_hash_rtx ( rtx  ,
int  ,
enum  machine_mode 
static unsigned int cselib_hash_rtx ( )
   Hash an rtx.  Return 0 if we couldn't hash the rtx.
   For registers and memory locations, we look up their cselib_val structure
   and return its VALUE element.
   Possible reasons for return 0 are: the object is volatile, or we couldn't
   find a register or memory location in the table and CREATE is zero.  If
   CREATE is nonzero, table elts are created for regs and mem.
   N.B. this hash function returns the same hash value for RTXes that
   differ only in the order of operands, thus it is suitable for comparisons
   that take commutativity into account.
   If we wanted to also support associative rules, we'd have to use a different
   strategy to avoid returning spurious 0, e.g. return ~(~0U >> 1) .
   MEMMODE indicates the mode of an enclosing MEM, and it's only
   used to compute autoinc values.
   We used to have a MODE argument for hashing for CONST_INTs, but that
   didn't make sense, since it caused spurious hash differences between
    (set (reg:SI 1) (const_int))
    (plus:SI (reg:SI 2) (reg:SI 1))
    (plus:SI (reg:SI 2) (const_int))
   If the mode is important in any context, it must be checked specifically
   in a comparison anyway, since relying on hash differences is unsafe.  
         ENTRY_VALUEs are function invariant, thus try to avoid
         recursing on argument if ENTRY_VALUE is one of the
         forms emitted by expand_debug_expr, otherwise
         ENTRY_VALUE hash would depend on the current value
         in some register or memory.  
         This is like the general case, except that it only counts
         the integers representing the constant.  
         Assume there is only one rtx object for any given label.  
         We don't hash on the address of the CODE_LABEL to avoid bootstrap
         differences and differences between each stage's debugging dumps.  
           Don't hash on the symbol's address to avoid bootstrap differences.
           Different hash values may cause expressions to be recorded in
           different orders and thus different registers to be used in the
           final assembler.  This also avoids differences in the dump files
           between various stages.  
         We can't compute these without knowing the MEM mode.  
         Adjust the hash so that (mem:MEMMODE (pre_* (reg))) hashes
         like (mem:MEMMODE (plus (reg) (const_int I))).  
bool cselib_have_permanent_equivalences ( void  )
   Return TRUE if any permanent equivalences have been recorded since
   the table was last initialized.  
void cselib_init ( )
   Initialize cselib for one pass.  The caller must also call
     (mem:BLK (scratch)) is a special mechanism to conflict with everything,
     see canon_true_dependence.  This is only created once.  
     We preserve reg_values to allow expensive clearing of the whole thing.
     Reallocate it however if it happens to be too large.  
         Some space for newly emit instructions so we don't end up
         reallocating in between passes.  

Referenced by chain_to_prev_insn_p().

static void cselib_invalidate_mem ( rtx  )
static void cselib_invalidate_mem ( )
   Invalidate any locations in the table which are changed because of a
   store to MEM_RTX.  If this is called because of a non-const call
   instruction, MEM_RTX is (mem:BLK const0_rtx).  
             MEMs may occur in locations only at the top level; below
             that every MEM or REG is substituted by its VALUE.  
             This one overlaps.  
             We must have a mapping from this MEM's address to the
             value (E).  Remove that, too.  
                 Record canonicalized elt.  

References cselib_val_struct::locs, new_elt_list(), new_elt_loc_list(), and cselib_val_struct::val_rtx.

static void cselib_invalidate_regno ( unsigned  int,
enum  machine_mode 
static void cselib_invalidate_regno ( )
   Invalidate any entries in reg_values that overlap REGNO.  This is called
   if REGNO is changing.  MODE is the mode of the assignment to REGNO, which
   is used to determine how many hard registers are being changed.  If MODE
   is VOIDmode, then only REGNO is being changed; this is used when
   invalidating call clobbered registers across a call.  
     If we see pseudos after reload, something is _wrong_.  
     Determine the range of registers that must be invalidated.  For
     pseudos, only REGNO is affected.  For hard regs, we must take MODE
     into account, and we must also invalidate lower register numbers
     if they contain values that overlap REGNO.  
         Go through all known values for this reg; if it overlaps the range
         we're invalidating, remove the value.  
             We have an overlap.  
                 Maintain the invariant that the first entry of
                 REG_VALUES, if present, must be the value used to set
                 the register, or NULL.  This is also nice because
                 then we won't push the same regno onto user_regs
                 multiple times.  
             Now, we clear the mapping from value to reg.  It must exist, so
             this code will crash intentionally if it doesn't.  

References cselib_val_struct::addr_list, canon_anti_dependence(), canonical_cselib_val(), cselib_lookup(), elt_list::next, elt_loc_list::next, unchain_one_elt_list(), and unchain_one_elt_loc_list().

void cselib_invalidate_rtx ( )
   Invalidate DEST, which is being assigned to or clobbered.  
static void cselib_invalidate_rtx_note_stores ( rtx  dest,
const_rtx  ignore,
void *  data 
   A wrapper for cselib_invalidate_rtx to be called via note_stores.  
cselib_val* cselib_lookup ( rtx  x,
enum machine_mode  mode,
int  create,
enum machine_mode  memmode 
   Wrapper for cselib_lookup_1, that logs the lookup result and
   maintains invariants related with debug insns.  
     ??? Should we return NULL if we're not to create an entry, the
     found loc is a debug loc and cselib_current_insn is not DEBUG?
     If so, we should also avoid converting val to non-DEBUG; probably
     easiest setting cselib_current_insn to NULL before the call

Referenced by add_stores(), cselib_invalidate_regno(), cselib_reg_set_mode(), dataflow_set_destroy(), debug_ilist(), and vt_stack_adjustments().

static cselib_val* cselib_lookup_1 ( rtx  x,
enum machine_mode  mode,
int  create,
enum machine_mode  memmode 
   Look up the rtl expression X in our tables and return the value it
   has.  If CREATE is zero, we return NULL if we don't know the value.
   Otherwise, we create a new one if possible, using mode MODE if X
   doesn't have a mode (i.e. because it's a constant).  When X is part
   of an address, MEMMODE should be the mode of the enclosing MEM if
   we're tracking autoinc expressions.  
             Maintain the invariant that the first entry of
             REG_VALUES, if present, must be the value used to set the
             register, or NULL.  
             During var-tracking, try harder to find equivalences
             for SUBREGs.  If a setter sets say a DImode register
             and user uses that register only in SImode, add a lowpart
             subreg location.  
     Can't even create if hashing is not possible.  
     We have to fill the slot before calling cselib_subst_to_values:
     the hash table is inconsistent until we do so, and
     cselib_subst_to_values will need to do lookups.  
cselib_val* cselib_lookup_from_insn ( rtx  x,
enum machine_mode  mode,
int  create,
enum machine_mode  memmode,
rtx  insn 
   Wrapper for cselib_lookup, that indicates X is in INSN.  

Referenced by sched_analyze_2().

static cselib_val* cselib_lookup_mem ( rtx  ,
static cselib_val* cselib_lookup_mem ( )
   Subroutine of cselib_lookup.  Return a value for X, which is a MEM rtx.
   If CREATE, make a new one if we haven't seen it before.  
     Look up the value for the address.  
     Find a value that describes a value of our mode at that address.  

References dump_file, elt_loc_list::loc, and print_inline_rtx().

void cselib_preserve_cfa_base_value ( )
   Arrange for a REG value to be assumed constant through the whole function,
   never invalidated and preserved across cselib_reset_table calls.  
void cselib_preserve_only_values ( void  )
   Clean all non-constant expressions in the hash table, but retain
   their values.  
void cselib_preserve_value ( )
   Arrange for a value to not be removed from the hash table even if
   it becomes useless.  

References cselib_val_struct::val_rtx.

Referenced by same_variable_part_p().

bool cselib_preserved_value_p ( )
   Test whether a value is preserved.  

Referenced by add_stores().

void cselib_process_insn ( )
   Record the effects of INSN.  
     Forget everything at a CODE_LABEL, a volatile insn, or a setjmp.  
     If this is a call instruction, forget anything stored in a
     call clobbered register, or, if this is not a const call, in
         Since it is not clear how cselib is going to be used, be
         conservative here and treat looping pure or const functions
         as if they were regular functions.  
     Look for any CLOBBERs in CALL_INSN_FUNCTION_USAGE, but only
     after we have processed the insn.  
         Flush evertything on setjmp.  
     On setter of the hard frame pointer if frame_pointer_needed,
     invalidate stack_pointer_rtx, so that sp and {,h}fp based
     VALUEs are distinct.  
         remove_useless_values is linear in the hash table size.  Avoid
         quadratic behavior for very large hashtables with very few
         useless elements.  

References cselib_val_struct::addr_list, elt_list::elt, elt_loc_list::loc, cselib_val_struct::locs, elt_list::next, elt_loc_list::next, cselib_val_struct::next_containing_mem, print_inline_rtx(), elt_loc_list::setting_insn, and cselib_val_struct::val_rtx.

Referenced by record_entry_value(), and reload_cse_regs_1().

static int cselib_record_autoinc_cb ( rtx  mem,
rtx  op,
rtx  dest,
rtx  src,
rtx  srcoff,
void *  arg 
   Callback for for_each_inc_dec.  Records in ARG the SETs implied by
   autoinc RTXs: SRC plus SRCOFF if non-NULL is stored in DEST.  
static void cselib_record_set ( rtx  ,
cselib_val ,
static void cselib_record_set ( )
   Record the result of a SET instruction.  DEST is being set; the source
   contains the value described by SRC_ELT.  If DEST is a MEM, DEST_ADDR_ELT
   describes its address.  
             The register should have been invalidated.  
static void cselib_record_sets ( rtx  )
static void cselib_record_sets ( )
   Record the effects of any sets and autoincs in INSN.  
     Find all sets.  
         Look through the PARALLEL and record the values being
         set, if possible.  Also handle any CLOBBERs.  
     Look up the values that are read.  Do this before invalidating the
     locations that are written.  
         A STRICT_LOW_PART can be ignored; we'll record the equivalence for
         the low part after invalidating any knowledge about larger modes.  
         We don't know how to record anything but REG or MEM.  
     Invalidate all locations written by this insn.  Note that the elts we
     looked up in the previous loop aren't affected, just some of their
     locations may go away.  
     If this is an asm, look for duplicate sets.  This can happen when the
     user uses the same value as an output multiple times.  This is valid
     if the outputs are not actually used thereafter.  Treat this case as
     if the value isn't actually set.  We do this by smashing the destination
     to pc_rtx, so that we won't record the value later.  
     Now enter the equivalences in our tables.  

References find_reg_note(), and modified_in_p().

enum machine_mode cselib_reg_set_mode ( )
   Return the mode in which a register was last set.  If X is not a
   register, return its mode.  If the mode in which the register was
   set is not known, or the value was already clobbered, return

References cselib_lookup().

void cselib_reset_table ( )
   Remove all entries from the hash table, arranging for the next
   value to be numbered NUM.  

Referenced by unchain_one_elt_list().

void cselib_set_value_sp_based ( )
   Arrange for a value to be marked as based on stack pointer
   for find_base_term purposes.  
bool cselib_sp_based_value_p ( )
   Test whether a value is based on stack pointer for
   find_base_term purposes.  

Referenced by rtx_equal_for_memref_p().

rtx cselib_subst_to_values ( )
   Walk rtx X and replace all occurrences of REG and MEM subexpressions
   with VALUE expressions.  This way, it becomes independent of changes
   to registers and memory.
   X isn't actually modified; if modifications are needed, new rtl is
   allocated.  However, the return value can share rtl with X.
   If X is within a MEM, MEMMODE must be the mode of the MEM.  
         This used to happen for autoincrements, but we deal with them
         properly now.  Remove the if stmt for the next release.  
             Assign a value that doesn't match any other.  
rtx cselib_subst_to_values_from_insn ( )
   Wrapper for cselib_subst_to_values, that indicates X is in INSN.  
int discard_useless_locs ( )
   For all locations found in X, delete locations that reference useless
   values (i.e. values without any location).  Called through

References canonical_cselib_val(), dummy_val, first_containing_mem, cselib_val_struct::locs, n_useless_debug_values, cselib_val_struct::next_containing_mem, and hash_table< Descriptor, Allocator >::traverse().

int discard_useless_values ( )
   If X is a value with no locations, remove it from the hashtable.  
void dump_cselib_table ( )
   Dump to OUT everything in the CSELIB table.  

Referenced by record_entry_value().

int dump_cselib_val ( )
   Dump the cselib_val *X to FILE *OUT.  
static rtx expand_loc ( struct elt_loc_list p,
struct expand_value_data evd,
int  max_depth 
   Search through the possible substitutions in P.  We prefer a non reg
   substitution because this allows us to expand the tree further.  If
   we find, just a reg, take the lowest regno.  There may be several
   non-reg results, we just take the first one because they will all
   expand to the same place.  
         Return these right away to avoid returning stack pointer based
         expressions for frame pointer and vice versa, which is something
         that would confuse DSE.  See the comment in cselib_expand_value_rtx_1
         for more details.  
         Avoid infinite recursion trying to expand a reg into a
         the same reg.  
         Avoid infinite recursion and do not try to expand the

References expand_value_data::callback, expand_value_data::callback_arg, cselib_expand_value_rtx_1(), expand_value_data::dummy, and expand_value_data::regs_active.

bool fp_setter_insn ( )
   Return true if INSN in the prologue initializes hard_frame_pointer_rtx.  
     Don't return true for frame pointer restores in the epilogue.  

References cfa_base_preserved_regno, cselib_any_perm_equivs, cselib_clear_table(), cselib_discard_hook, cselib_preserve_constants, hash_table< Descriptor, Allocator >::dispose(), free(), and free_alloc_pool().

static bool invariant_or_equiv_p ( )
   Return TRUE if V is a constant, a function invariant or a VALUE
   equivalence; FALSE otherwise.  
     Keep VALUE equivalences around.  
         Although a debug expr may be bound to different expressions,
         we can preserve it as if it was constant, to get unification
         and proper merging within var-tracking.  
         (plus (value V) (const_int C)) is invariant iff V is invariant.  

References hash_table< Descriptor, Allocator >::clear_slot().

static cselib_val* new_cselib_val ( unsigned  int,
enum  machine_mode,
static cselib_val* new_cselib_val ( )
   Create a new value structure for VALUE and initialize it.  The mode of the
   value is MODE.  
     We use an alloc pool to allocate this RTL construct because it
     accounts for about 8% of the overall memory usage.  We know
     precisely when we can have VALUE RTXen (when cselib is active)
     so we don't need to put them in garbage collected memory.
     ??? Why should a VALUE be an RTX in the first place?  
static struct elt_list* new_elt_list ( struct elt_list ,

Referenced by cselib_invalidate_mem().

static struct elt_list* new_elt_list ( )
   Allocate a struct elt_list and fill in its two elements with the
static void new_elt_loc_list ( cselib_val ,

Referenced by cselib_invalidate_mem().

static void new_elt_loc_list ( )
   Allocate a struct elt_loc_list with LOC and prepend it to VAL's loc
     If we're creating the first loc in a debug insn context, we've
     just created a debug value.  Count it.  
             Reverse the insertion.  
             Bring all locs from LOC to VAL.  
                 Adjust values that have LOC as canonical so that VAL
                 becomes their canonical.  
             Bring in addr_list into canonical node.  
             Add VAL to the containing_mem list after LOC.  LOC will
             be removed when we notice it doesn't contain any
         Chain LOC back to VAL.  
int preserve_constants_and_equivs ( )
   Remove from hash table all VALUEs except constants, function
   invariants and VALUE equivalences.  

References cselib_any_perm_equivs, and hash_table< Descriptor, Allocator >::empty().

static void promote_debug_loc ( struct elt_loc_list l)
static void promote_debug_loc ( )
   Promote loc L to a nondebug cselib_current_insn if L is marked as
   originating from a debug insn, maintaining the debug values

References elt_loc_list::next, and pool_free().

int references_value_p ( )
   Return true if X contains a VALUE rtx.  If ONLY_USELESS is set, we
   only return true for values which point to a cselib_val whose value
   element has been set to zero, which implies the cselib_val will be

Referenced by cselib_find_slot().

static void remove_useless_values ( )
   Clean out useless values (i.e. those which no longer have locations
   associated with them) from the hash table.  
     First pass: eliminate locations that reference the value.  That in
     turn can make more values useless.  
     Second pass: actually remove the values.  

References cfa_base_preserved_regno, cselib_preserve_constants, elt_loc_list::loc, and cselib_val_struct::locs.

static int rtx_equal_for_cselib_1 ( rtx  ,
rtx  ,
enum  machine_mode 
static int rtx_equal_for_cselib_1 ( )
   Return nonzero if we can prove that X and Y contain the same value,
   taking our gathered information into account.  MEMMODE holds the
   mode of the enclosing MEM, if any, as required to deal with autoinc
   addressing modes.  If X and Y are not (known to be) part of
   addresses, MEMMODE should be VOIDmode.  
             Avoid infinite recursion.  We know we have the canonical
             value, so we can just skip any values in the equivalence
         Don't recurse if nothing changed.  
     These won't be handled correctly by the code below.  
         ENTRY_VALUEs are function invariant, it is thus undesirable to
         use rtx_equal_for_cselib_1 to compare the operands.  
         We have to compare any autoinc operations in the addresses
         using this MEM's mode.  
             Two vectors must have the same length.  
             And the corresponding elements must match.  
             These are just backpointers, so they don't matter.  
             It is believed that rtx's at this level will never
             contain anything but integers and other rtx's,
             except for within LABEL_REFs and SYMBOL_REFs.  
int rtx_equal_for_cselib_p ( )
   Return nonzero if we can prove that X and Y contain the same value, taking
   our gathered information into account.  
static void unchain_one_elt_list ( struct elt_list **  )

Referenced by cselib_invalidate_regno().

static void unchain_one_elt_list ( )
   The elt_list at *PL is no longer needed.  Unchain it and free its

References cselib_reset_table().

static void unchain_one_elt_loc_list ( struct elt_loc_list **  )
static void unchain_one_elt_loc_list ( )
   Likewise for elt_loc_lists.  

References elt_loc_list::loc, and cselib_val_struct::locs.

static void unchain_one_value ( cselib_val )
static void unchain_one_value ( )
   Likewise for cselib_vals.  This also frees the addr_list associated with
static rtx wrap_constant ( )
   We need to pass down the mode of constants through the hash table
   functions.  For that purpose, wrap them in a CONST of the appropriate

Variable Documentation

rtx callmem
   We pass this to cselib_invalidate_mem to invalidate all of
   memory for a non-const call instruction.  
unsigned int cfa_base_preserved_regno = INVALID_REGNUM
cselib_val* cfa_base_preserved_val
   If non-NULL, value of the eliminated arg_pointer_rtx or frame_pointer_rtx
   that is constant through the whole function and should never be
bool cselib_any_perm_equivs
rtx cselib_current_insn
   This is a global so we don't have to pass this through every function.
   It is used in new_elt_loc_list to set SETTING_INSN.  
void(* cselib_discard_hook)(cselib_val *)
   If nonnull, cselib will call this function before freeing useless
   VALUEs.  A VALUE is deemed useless if its "locs" field is null.  

Referenced by fp_setter_insn().

hash_table<cselib_hasher> cselib_hash_table
   A table that enables us to look up elts by their value.  
unsigned int cselib_nregs
   The number of registers we had when the varrays were last resized.  
bool cselib_preserve_constants
bool cselib_record_memory
void(* cselib_record_sets_hook)(rtx insn, struct cselib_set *sets, int n_sets)
   If nonnull, cselib will call this function before recording sets or
   even clobbering outputs of INSN.  All the recorded sets will be
   represented in the array sets[n_sets].  new_val_min can be used to
   tell whether values present in sets are introduced by this
alloc_pool cselib_val_pool
cselib_val dummy_val
   Used as stop element of the containing_mem list so we can check
   presence in the list by checking the next pointer.  

Referenced by discard_useless_locs().

alloc_pool elt_list_pool
alloc_pool elt_loc_list_pool
enum machine_mode find_slot_memmode
   See the documentation of cselib_find_slot below.  
cselib_val* first_containing_mem = &dummy_val
   Used to list all values that contain memory reference.
   May or may not contain the useless values - the list is compacted
   each time memory is invalidated.  

Referenced by discard_useless_locs().

unsigned int max_value_regs
   The largest number of hard regs used by any entry added to the
   REG_VALUES table.  Cleared on each cselib_clear_table() invocation.  
int n_debug_values
   Count values whose locs have been taken exclusively from debug
   insns for the entire life of the value.  
unsigned int n_used_regs
int n_useless_debug_values

Referenced by discard_useless_locs().

int n_useless_values
   Count values without known locations, or with only locations that
   wouldn't have been known except for debug insns.  Whenever this
   grows too big, we remove these useless values from the table.

   Counting values with only debug values is a bit tricky.  We don't
   want to increment n_useless_values when we create a value for a
   debug insn, for this would get n_useless_values out of sync, but we
   want increment it if all locs in the list that were ever referenced
   in nondebug insns are removed from the list.

   In the general case, once we do that, we'd have to stop accepting
   nondebug expressions in the loc list, to avoid having two values
   equivalent that, without debug insns, would have been made into
   separate values.  However, because debug insns never introduce
   equivalences themselves (no assignments), the only means for
   growing loc lists is through nondebug assignments.  If the locs
   also happen to be referenced in debug insns, it will work just fine.

   A consequence of this is that there's at most one debug-only loc in
   each loc list.  If we keep it in the first entry, testing whether
   we have a debug-only loc list takes O(1).

   Furthermore, since any additional entry in a loc list containing a
   debug loc would have to come from an assignment (nondebug) that
   references both the initial debug loc and the newly-equivalent loc,
   the initial debug loc would be promoted to a nondebug loc, and the
   loc list would not contain debug locs any more.

   So the only case we have to be careful with in order to keep
   n_useless_values in sync between debug and nondebug compilations is
   to avoid incrementing n_useless_values when removing the single loc
   from a value that turns out to not appear outside debug values.  We
   increment n_useless_debug_values instead, and leave such values
   alone until, for other reasons, we garbage-collect useless
unsigned int next_uid
   The unique id that the next create value will take.  
struct elt_list** reg_values
   This table maps from register number to values.  It does not
   contain pointers to cselib_val structures, but rather elt_lists.
   The purpose is to be able to refer to the same register in
   different modes.  The first element of the list defines the mode in
   which the register was set; if the mode is unknown or the value is
   no longer valid in that mode, ELT will be NULL for the first
unsigned int reg_values_size
unsigned int* used_regs
   Here the set of indices I with REG_VALUES(I) != 0 is saved.  This is used
   in cselib_clear_table() for fast emptying.  

Referenced by saved_hard_reg_compare_func().

alloc_pool value_pool
int values_became_useless
   Set by discard_useless_locs if it deleted the last location of any