#include "config.h"#include "system.h"#include "coretypes.h"#include "tm.h"#include "tree.h"#include "flags.h"#include "tm_p.h"#include "langhooks.h"#include "basic-block.h"#include "function.h"#include "gimple-pretty-print.h"#include "gimple.h"#include "gimple-ssa.h"#include "tree-cfg.h"#include "tree-phinodes.h"#include "ssa-iterators.h"#include "tree-ssanames.h"#include "tree-into-ssa.h"#include "tree-dfa.h"#include "tree-ssa.h"#include "tree-inline.h"#include "hash-table.h"#include "tree-pass.h"#include "cfgloop.h"#include "domwalk.h"#include "params.h"#include "diagnostic-core.h"
Data Structures | |
| struct | def_blocks_d |
| struct | mark_def_sites_global_data |
| struct | common_info_d |
| struct | var_info_d |
| struct | var_info_hasher |
| struct | ssa_name_info |
| struct | dom_dfsnum |
| class | rewrite_dom_walker |
| class | rewrite_update_dom_walker |
| class | mark_def_dom_walker |
Macros | |
| #define | NAME_SETS_GROWTH_FACTOR (MAX (3, num_ssa_names / 3)) |
Typedefs | |
| typedef struct def_blocks_d * | def_blocks_p |
| typedef struct common_info_d * | common_info_p |
| typedef struct var_info_d * | var_info_p |
| typedef struct ssa_name_info * | ssa_name_info_p |
Enumerations | |
| enum | need_phi_state { NEED_PHI_STATE_UNKNOWN, NEED_PHI_STATE_NO, NEED_PHI_STATE_MAYBE } |
| enum | rewrite_mode { REWRITE_ALL, REWRITE_UPDATE } |
Variables | |
| static vec< tree > | block_defs_stack |
| static sbitmap | old_ssa_names |
| static sbitmap | new_ssa_names |
| static sbitmap | interesting_blocks |
| static bitmap | names_to_release |
| static vec< gimple_vec > | phis_to_rewrite |
| static bitmap | blocks_with_phis_to_rewrite |
| static struct function * | update_ssa_initialized_fn = NULL |
| static hash_table < var_info_hasher > | var_infos |
| static vec< ssa_name_info_p > | info_for_ssa_name |
| static unsigned | current_info_for_ssa_name_age |
| static bitmap_obstack | update_ssa_obstack |
| static bitmap | blocks_to_update |
| static bitmap | symbols_to_rename_set |
| static vec< tree > | symbols_to_rename |
Macro Definition Documentation
| #define NAME_SETS_GROWTH_FACTOR (MAX (3, num_ssa_names / 3)) |
Growth factor for NEW_SSA_NAMES and OLD_SSA_NAMES. These sets need to grow as the callers to create_new_def_for will create new names on the fly. FIXME. Currently set to 1/3 to avoid frequent reallocations but still need to find a reasonable growth strategy.
Typedef Documentation
| typedef struct common_info_d* common_info_p |
The information associated with decls and SSA names.
| typedef struct def_blocks_d* def_blocks_p |
| typedef struct ssa_name_info* ssa_name_info_p |
The information associated with names.
| typedef struct var_info_d* var_info_p |
The information associated with decls.
Enumeration Type Documentation
| enum need_phi_state |
It is advantageous to avoid things like life analysis for variables which do not need PHI nodes. This enum describes whether or not a particular variable may need a PHI node.
- Enumerator:
| enum rewrite_mode |
The main entry point to the SSA renamer (rewrite_blocks) may be called several times to do different, but related, tasks. Initially, we need it to rename the whole program into SSA form. At other times, we may need it to only rename into SSA newly exposed symbols. Finally, we can also call it to incrementally fix an already built SSA web.
Function Documentation
|
static |
Add a new mapping NEW_TREE -> OLD REPL_TBL. Every entry N_i in REPL_TBL represents the set of names O_1 ... O_j replaced by N_i. This is used by update_ssa and its helpers to introduce new SSA names in an already formed SSA web.
OLD and NEW_TREE must be different SSA names for the same symbol.
We may need to grow NEW_SSA_NAMES and OLD_SSA_NAMES because our caller may have created new names since the set was created.
Update the REPL_TBL table.
If OLD had already been registered as a new name, then all the names that OLD replaces should also be replaced by NEW_TREE.
Register NEW_TREE and OLD in NEW_SSA_NAMES and OLD_SSA_NAMES, respectively.
References bitmap_bit_p, DECL_P, DECL_UID, gcc_checking_assert, set_livein_block(), set_rewrite_uses(), and USE_FROM_PTR.
|
inlinestatic |
Add OLD to REPL_TBL[NEW_TREE].SET.
|
static |
Clears info for SSA names.
If current_info_for_ssa_name_age wraps we use stale information. Asser that this does not happen.
|
static |
Compares two entries of type struct dom_dfsnum by dfs_num field. Callback for qsort.
References BASIC_BLOCK, bb_dom_dfs_in(), bb_dom_dfs_out(), dom_dfsnum::bb_index, CDI_DOMINATORS, and dom_dfsnum::dfs_num.
| tree create_new_def_for | ( | ) |
Create a new name for OLD_NAME in statement STMT and replace the operand pointed to by DEF_P with the newly created name. If DEF_P is NULL then STMT should be a GIMPLE assignment. Return the new name and register the replacement mapping <NEW, OLD> in update_ssa's tables.
If needed, mark NEW_NAME as occurring in an abnormal PHI node.
For the benefit of passes that will be updating the SSA form on their own, set the current reaching definition of OLD_NAME to be NEW_NAME.
Referenced by gimple_redirect_edge_and_branch().
| DEBUG_FUNCTION void debug_currdefs | ( | void | ) |
Dump the current reaching definition of every symbol to stderr.
References DECL_P, get_reaching_def(), marked_for_renaming(), NULL_TREE, SSA_NAME_VAR, and USE_FROM_PTR.
| DEBUG_FUNCTION void debug_decl_set | ( | ) |
Dump bitmap SET (assumed to contain VAR_DECLs) to FILE.
| DEBUG_FUNCTION void debug_defs_stack | ( | ) |
Dump the renaming stack (block_defs_stack) to stderr. Traverse the stack up to a maximum of N levels. If N is -1, the whole stack is dumped. New levels are created when the dominator tree traversal used for renaming enters a new sub-tree.
References get_common_info().
| DEBUG_FUNCTION void debug_names_replaced_by | ( | ) |
Dump all the names replaced by NAME to stderr.
References gcc_assert, is_new_name(), and is_old_name().
| DEBUG_FUNCTION void debug_tree_ssa | ( | void | ) |
Dump SSA information to stderr.
References get_ssa_name_ann(), ssa_name_info::info, and SSA_NAME_IS_DEFAULT_DEF.
| DEBUG_FUNCTION void debug_tree_ssa_stats | ( | void | ) |
Dump SSA statistics on stderr.
References gimple_build_debug_bind, make_ssa_name(), SET_DEF, and target_for_debug_bind().
| DEBUG_FUNCTION void debug_update_ssa | ( | void | ) |
Dump SSA update information to stderr.
| DEBUG_FUNCTION void debug_var_infos | ( | void | ) |
Dump the VAR_INFOS hash table on stderr.
| int debug_var_infos_r | ( | ) |
Callback for htab_traverse to dump the VAR_INFOS hash table.
References edge_def::flags, FOR_EACH_EDGE, gcc_checking_assert, gsi_bb(), NULL, and basic_block_def::succs.
| void delete_update_ssa | ( | void | ) |
Deallocate data structures used for incremental SSA updates.
References bitmap_copy(), gcc_checking_assert, and TODO_update_ssa_full_phi.
Referenced by ssa_name_has_uses_outside_loop_p().
| void dump_currdefs | ( | ) |
Dump the current reaching definition of every symbol to FILE.
| void dump_defs_stack | ( | ) |
Dump the renaming stack (block_defs_stack) to FILE. Traverse the stack up to a maximum of N levels. If N is -1, the whole stack is dumped. New levels are created when the dominator tree traversal used for renaming enters a new sub-tree.
| void dump_names_replaced_by | ( | ) |
Dump all the names replaced by NAME to FILE.
References dump_file, print_gimple_stmt(), and TDF_SLIM.
Referenced by prepare_block_for_update().
| void dump_tree_ssa | ( | ) |
Dump SSA information to FILE.
| void dump_tree_ssa_stats | ( | ) |
Dump SSA statistics on FILE.
References DECL_P, DEF_FROM_PTR, marked_for_renaming(), and SSA_NAME_VAR.
| void dump_update_ssa | ( | ) |
Dump SSA update information to FILE.
References BITMAP_ALLOC, bitmap_set_bit, gcc_assert, NULL, and SSA_NAME_VERSION.
| void dump_var_infos | ( | ) |
Dump the VAR_INFOS hash table on FILE.
References gsi_insert_on_edge_immediate().
|
staticread |
Return the set of blocks where variable VAR is defined and the blocks where VAR is live on entry (livein). Return NULL, if no entry is found in DEF_BLOCKS.
References create_phi_node(), DECL_P, gcc_checking_assert, and target_for_debug_bind().
|
static |
Among the intervals starting at the N points specified in DEFS, find the one that contains S, and return its bb_index.
|
static |
Deallocate internal data structures used by the renamer.
|
static |
Gate for IPCP optimization.
Do nothing for funcions that was produced already in SSA form.
Referenced by rewrite_blocks().
|
inlinestatic |
Get access to the auxiliar information stored per SSA name or decl.
References bitmap_set_bit, gcc_checking_assert, basic_block_def::index, initialize_flags_in_bb(), and NULL.
Referenced by debug_defs_stack(), get_var_info(), initialize_flags_in_bb(), and insert_phi_nodes_compare_var_infos().
| tree get_current_def | ( | ) |
Return the current definition for VAR.
References BITMAP_ALLOC, and def_blocks_d::def_blocks.
|
staticread |
Return the set of blocks where variable VAR is defined and the blocks where VAR is live on entry (livein). If no entry is found in DEF_BLOCKS, a new one is created and returned.
Referenced by initialize_flags_in_bb().
|
static |
Perform a depth-first traversal of the dominator tree looking for variables to rename. BB is the block where to start searching. Renaming is a five step process:
1- Every definition made by PHI nodes at the start of the blocks is registered as the current definition for the corresponding variable.
2- Every statement in BB is rewritten. USE and VUSE operands are rewritten with their corresponding reaching definition. DEF and VDEF targets are registered as new definitions.
3- All the PHI nodes in successor blocks of BB are visited. The argument corresponding to BB is replaced with its current reaching definition.
4- Recursively rewrite every dominator child block of BB.
5- Restore (in reverse order) the current reaching definition for every new definition introduced in this block. This is done so that when we return from the recursive call, all the current reaching definitions are restored to the names that were valid in the dominator parent of BB. Return the current definition for variable VAR. If none is found, create a new SSA name to act as the zeroth definition for VAR.
Lookup the current reaching definition for VAR.
If there is no reaching definition for VAR, create and register a default definition for it (if needed).
Return the current reaching definition for VAR, or the default definition, if we had to create one.
Referenced by debug_currdefs(), maybe_register_def(), and rewrite_debug_stmt_uses().
|
inlinestatic |
Get the information associated with NAME.
Re-allocate the vector at most once per update/into-SSA.
But allocate infos lazily.
Referenced by debug_tree_ssa(), and set_livein_block().
|
inlinestatic |
Return and allocate the auxiliar information for DECL.
References get_common_info().
|
static |
Dump statistics for the hash table HTAB.
|
static |
Initialize internal data needed during renaming.
Allocate memory for the DEF_BLOCKS hash table.
|
static |
Initialize data structures used for incremental SSA updates.
Reserve more space than the current number of names. The calls to add_new_name_mapping are typically done after creating new SSA names, so we'll need to reallocate these arrays.
|
static |
Cleans up the REWRITE_THIS_STMT and REGISTER_DEFS_IN_THIS_STMT flags for all statements in basic block BB.
We are going to use the operand cache API, such as SET_USE, SET_DEF, and FOR_EACH_IMM_USE_FAST. The operand cache for each statement should be up-to-date.
References bitmap_set_bit, def_blocks_d::def_blocks, get_common_info(), get_def_blocks_for(), basic_block_def::index, NEED_PHI_STATE_NO, NEED_PHI_STATE_UNKNOWN, and def_blocks_d::phi_blocks.
Referenced by get_common_info().
|
static |
Insert PHI nodes at the dominance frontier of blocks with variable definitions. DFS contains the dominance frontier information for the flowgraph.
Do two stages to avoid code generation differences for UID differences but no UID ordering differences.
References cfun, DECL_P, get_or_create_ssa_default_def(), and SSA_NAME_VAR.
|
static |
Sort var_infos after DECL_UID of their var.
References get_common_info().
|
static |
Insert PHI nodes for variable VAR using the iterated dominance frontier given in PHI_INSERTION_POINTS. If UPDATE_P is true, this function assumes that the caller is incrementally updating the existing SSA form, in which case VAR may be an SSA name instead of a symbol.
PHI_INSERTION_POINTS is updated to reflect nodes that already had a PHI node for VAR. On exit, only the nodes that received a PHI node for VAR will be present in PHI_INSERTION_POINTS.
Remove the blocks where we already have PHI nodes for VAR.
Remove obviously useless phi nodes.
And insert the PHI nodes.
If we are rewriting SSA names, create the LHS of the PHI
node by duplicating VAR. This is useful in the case of
pointers, to also duplicate pointer attributes (alias
information, in particular). Add VAR to every argument slot of PHI. We need VAR in
every argument so that rewrite_update_phi_arguments knows
which name is this PHI node replacing. If VAR is a
symbol marked for renaming, this is not necessary, the
renamer will use the symbol on the LHS to get its
reaching definition. Mark this PHI node as interesting for update_ssa.
|
static |
Sort symbols_to_rename after their DECL_UID.
|
static |
Insert new PHI nodes to replace VAR. DFS contains dominance frontier information. BLOCKS is the set of blocks to be updated.
This is slightly different than the regular PHI insertion algorithm. The value of UPDATE_FLAGS controls how PHI nodes for real names (i.e., GIMPLE registers) are inserted:
If UPDATE_FLAGS == TODO_update_ssa, we are only interested in PHI nodes inside the region affected by the block that defines VAR and the blocks that define all its replacements. All these definition blocks are stored in DEF_BLOCKS[VAR]->DEF_BLOCKS.
First, we compute the entry point to the region (ENTRY). This is given by the nearest common dominator to all the definition blocks. When computing the iterated dominance frontier (IDF), any block not strictly dominated by ENTRY is ignored.
We then call the standard PHI insertion algorithm with the pruned IDF.
- If UPDATE_FLAGS == TODO_update_ssa_full_phi, the IDF for real names is not pruned. PHI nodes are inserted at every IDF block.
Get all the definition sites for VAR.
No need to do anything if there were no definitions to VAR.
Compute the initial iterated dominance frontier.
If doing regular SSA updates for GIMPLE registers, we are
only interested in IDF blocks dominated by the nearest
common dominator of all the definition blocks. Otherwise, do not prune the IDF for VAR.
Otherwise, VAR is a symbol that needs to be put into SSA form
for the first time, so we need to compute the full IDF for
it. Make sure that PRUNED_IDF blocks and all their feeding blocks
are included in the region to be updated. The feeding blocks
are important to guarantee that the PHI arguments are renamed
properly. FIXME, this is not needed if we are updating symbols. We are
already starting at the ENTRY block anyway.
References internal_error(), print_generic_expr(), and TDF_SLIM.
|
inlinestatic |
Return true if NAME is in NEW_SSA_NAMES.
Referenced by debug_names_replaced_by(), and register_new_update_single().
|
inlinestatic |
Return true if NAME is in OLD_SSA_NAMES.
Referenced by debug_names_replaced_by(), maybe_register_def(), and register_new_update_single().
| gimple_opt_pass* make_pass_build_ssa | ( | ) |
References bitmap_bit_p, gcc_checking_assert, gimple_bb(), NULL, SSA_NAME_DEF_STMT, and SSA_NAME_VERSION.
|
static |
Mark block BB as interesting for update_ssa.
Referenced by mark_def_dom_walker::before_dom_children(), and mark_def_interesting().
|
static |
Mark the definition of VAR at STMT and BB as interesting for the renamer. BLOCKS is the set of blocks that need updating.
If VAR is an SSA name in NEW_SSA_NAMES, this is a definition site for both itself and all the old names replaced by it.
References gcc_checking_assert, basic_block_def::index, last_basic_block, and mark_block_for_update().
|
static |
Call back for walk_dominator_tree used to collect definition sites for every variable in the function. For every statement S in block BB:
1- Variables defined by S in the DEFS of S are marked in the bitmap KILLS.
2- If S uses a variable VAR and there is no preceding kill of VAR, then it is marked in the LIVEIN_BLOCKS bitmap associated with VAR.
This information is used to determine which variables are live across block boundaries to reduce the number of PHI nodes we create.
Since this is the first time that we rewrite the program into SSA form, force an operand scan on every statement.
If a variable is used before being set, then the variable is live across a block boundary, so mark it live-on-entry to BB.
Now process the defs. Mark BB as the definition block and add each def to the set of killed symbols.
If we found the statement interesting then also mark the block BB as interesting.
References dom_dfsnum::bb_index, and dom_dfsnum::dfs_num.
|
static |
Mark SYM for renaming.
References GF_PLF_1, and gimple_plf().
|
static |
Marks phi node PHI in basic block BB for rewrite.
References gimple_build_debug_bind, gsi_after_labels(), gsi_insert_before(), GSI_SAME_STMT, PHI_RESULT, and si.
|
inlinestatic |
Mark the use of VAR at STMT and BB as interesting for the renamer. INSERT_PHI_P is true if we are going to insert new PHI nodes.
If VAR has not been defined in BB, then it is live-on-entry to BB. Note that we cannot just use the block holding VAR's definition because if VAR is one of the names in OLD_SSA_NAMES, it will have several definitions (itself and all the names that replace it).
References bitmap_bit_p, NULL, prepare_def_site_for(), prepare_use_sites_for(), and ssa_name.
| void mark_virtual_operand_for_renaming | ( | ) |
Replace all uses of NAME by underlying variable and mark it for renaming. This assumes the defining statement of NAME is going to be removed.
Referenced by delete_worklist().
| void mark_virtual_operands_for_renaming | ( | ) |
Mark virtual operands of FN for renaming by update_ssa.
| void mark_virtual_phi_result_for_renaming | ( | ) |
Replace all uses of the virtual PHI result by its underlying variable and mark it for renaming. This assumes the PHI node is going to be removed.
|
static |
Return true if SYM is marked for renaming.
References GF_PLF_1, and gimple_set_plf().
Referenced by debug_currdefs(), dump_tree_ssa_stats(), and maybe_register_def().
|
inlinestatic |
If the operand pointed to by DEF_P is an SSA name in NEW_SSA_NAMES or OLD_SSA_NAMES, or if it is a symbol marked for renaming, register it as the current definition for the names replaced by DEF_P.
If DEF is a naked symbol that needs renaming, create a new name for it.
If stmt ends the bb, insert the debug stmt on the single
non-EH edge from the stmt. If there are other predecessors to ef->dest, then
there must be PHI nodes for the modified
variable, and therefore there will be debug bind
stmts after the PHI nodes. The debug bind notes
we'd insert would force the creation of a new
block (diverging codegen) and be redundant with
the post-PHI bind stmts, so don't add them.
As for the exit edge, there wouldn't be redundant
bind stmts, but there wouldn't be a PC to bind
them to either, so avoid diverging the CFG. If there were PHI nodes in the node, we'd
have to make sure the value we're binding
doesn't need rewriting. But there shouldn't
be PHI nodes in a single-predecessor block,
so we just add the note. If DEF is a new name, register it as a new definition
for all the names replaced by DEF. If DEF is an old name, register DEF as a new
definition for itself.
References DECL_P, edge_def::flags, gcc_checking_assert, get_reaching_def(), gimple_location(), gimple_phi_arg_location(), gimple_phi_arg_set_location(), gimple_phi_num_args(), gimple_phi_result(), is_old_name(), marked_for_renaming(), NULL, NULL_TREE, PHI_ARG_DEF_PTR_FROM_EDGE, PHI_ARG_INDEX_FROM_USE, rewrite_uses_p(), SET_USE, SSA_NAME_DEF_STMT, SSA_NAME_OCCURS_IN_ABNORMAL_PHI, SSA_NAME_VAR, TREE_CODE, UNKNOWN_LOCATION, USE_FROM_PTR, and virtual_operand_p().
|
inlinestatic |
If the operand pointed to by USE_P is a name in OLD_SSA_NAMES or it is a symbol marked for renaming, replace it with USE_P's current reaching definition.
|
inlinestatic |
Same as maybe_replace_use, but without introducing default stmts, returning false to indicate a need to do so.
We can't assume that, if there's no current definition, the default one should be used. It could be the case that we've rearranged blocks so that the earlier definition no longer dominates the use.
| bool name_registered_for_update_p | ( | ) |
Return true if name N has been registered in the replacement table.
Referenced by find_released_ssa_name().
|
inlinestatic |
Return the names replaced by NEW_TREE (i.e., REPL_TBL[NEW_TREE].SET).
References update_stmt().
Referenced by register_new_update_single().
| bool need_ssa_update_p | ( | ) |
Return true if there is any work to be done by update_ssa for function FN.
References bitmap_clear().
Referenced by prepare_block_for_update(), and standard_iv_increment_position().
|
static |
Do a dominator walk starting at BB processing statements that reference symbols in SSA operands. This is very similar to mark_def_sites, but the scan handles statements whose operands may already be SSA names.
If INSERT_PHI_P is true, mark those uses as live in the corresponding block. This is later used by the PHI placement algorithm to make PHI pruning decisions.
FIXME. Most of this would be unnecessary if we could associate a symbol to all the SSA names that reference it. But that sounds like it would be expensive to maintain. Still, it would be interesting to see if it makes better sense to do that.
Process PHI nodes marking interesting those that define or use the symbols that we are interested in.
Mark the uses in phi nodes as interesting. It would be more correct
to process the arguments of the phi nodes of the successor edges of
BB at the end of prepare_block_for_update, however, that turns out
to be significantly more expensive. Doing it here is conservatively
correct – it may only cause us to believe a value to be live in a
block that also contains its definition, and thus insert a few more
phi nodes for it. Process the statements.
Now visit all the blocks dominated by BB.
References bitmap_empty_p(), bitmap_first_set_bit(), cfun, dump_decl_set(), dump_names_replaced_by(), EXECUTE_IF_SET_IN_BITMAP, need_ssa_update_p(), print_generic_expr(), and ssa_name.
|
static |
Helper for prepare_names_to_update. Mark the definition site for NAME as interesting. BLOCKS and INSERT_PHI_P are as in prepare_names_to_update.
Referenced by mark_use_interesting().
|
static |
Mark definition and use sites of names in NEW_SSA_NAMES and OLD_SSA_NAMES. INSERT_PHI_P is true if the caller wants to insert PHI nodes for newly created names.
If a name N from NEW_SSA_NAMES is also marked to be released, remove it from NEW_SSA_NAMES so that we don't try to visit its defining basic block (which most likely doesn't exist). Notice that we cannot do the same with names in OLD_SSA_NAMES because we want to replace existing instances.
First process names in NEW_SSA_NAMES. Otherwise, uses of old names may be considered to be live-in on blocks that contain definitions for their replacements.
If an old name is in NAMES_TO_RELEASE, we cannot remove it from OLD_SSA_NAMES, but we have to ignore its definition site.
|
static |
Helper for prepare_names_to_update. Mark all the use sites for NAME as interesting. BLOCKS and INSERT_PHI_P are as in prepare_names_to_update.
For regular statements, mark this as an interesting use for NAME.
Referenced by mark_use_interesting().
|
static |
Clean bits from PHIS for phi nodes whose value cannot be used in USES. KILLS is a bitmap of blocks where the value is defined before any use.
The phi must dominate a use, or an argument of a live phi. Also, we do not create any phi nodes in def blocks, unless they are also livein.
We want to remove the unnecessary phi nodes, but we do not want to compute liveness information, as that may be linear in the size of CFG, and if there are lot of different variables to rewrite, this may lead to quadratic behavior. Instead, we basically emulate standard dce. We put all uses to worklist, then for each of them find the nearest def that dominates them. If this def is a phi node, we mark it live, and if it was not live before, we add the predecessors of its basic block to the worklist. To quickly locate the nearest def that dominates use, we use dfs numbering of the dominance tree (that is already available in order to speed up queries). For each def, we have the interval given by the dfs number on entry to and on exit from the corresponding subtree in the dominance tree. The nearest dominator for a given use is the smallest of these intervals that contains entry and exit dfs numbers for the basic block with the use. If we store the bounds for all the uses to an array and sort it, we can locate the nearest dominating def in logarithmic time by binary search.
Now each DEFS entry contains the number of the basic block to that the dfs number corresponds. Change them to the number of basic block that corresponds to the interval following the dfs number. Also, for the dfs_out numbers, increase the dfs number by one (so that it corresponds to the start of the following interval, not to the end of the current one). We use WORKLIST as a stack.
This is a closing element. Interval corresponding to the top
of the stack after removing it follows. Opening element. Nothing to do, just push it to the stack and move
it to the correct position. If this interval starts at the same point as the previous one, cancel
the previous one. Now process the uses.
If there is a phi node in USE_BB, it is made live. Otherwise,
find the def that dominates the immediate dominator of USE_BB
(the kill in USE_BB does not dominate the use). If the phi node is already live, there is nothing to do.
Add the new uses to the worklist.
In case there is a kill directly in the use block, do not record
the use (this is also necessary for correctness, as we assume that
uses dominated by a def directly in their block have been filtered
out before).
|
inlinestatic |
Return true if the DEFs created by statement STMT should be registered when marking new definition sites. This is slightly different than rewrite_uses_p: it's used by update_ssa to distinguish statements that need to have both uses and defs processed from those that only need to have their defs processed. Statements that define new SSA names only need to have their defs registered, but they don't need to have their uses renamed.
|
static |
Push SYM's current reaching definition into BLOCK_DEFS_STACK and register DEF (an SSA_NAME) to be a new definition for SYM.
If this variable is set in a single basic block and all uses are dominated by the set(s) in that single basic block, then there is no reason to record anything for this variable in the block local definition stacks. Doing so just wastes time and memory. This is the same test to prune the set of variables which may need PHI nodes. So we just use that information since it's already computed and available for us to use.
If SYM is not a GIMPLE register, then CURRDEF may be a name whose SSA_NAME_VAR is not necessarily SYM. In this case, also push SYM in the stack so that we know which symbol is being defined by this SSA name when we unwind the stack.
Push the current reaching definition into BLOCK_DEFS_STACK. This stack is later used by the dominator tree callbacks to restore the reaching definitions for all the variables defined in the block after a recursive visit to all its immediately dominated blocks. If there is no current reaching definition, then just record the underlying _DECL node.
Set the current reaching definition for SYM to be DEF.
References gimple_debug_source_bind_get_value(), gimple_debug_source_bind_get_var(), gimple_debug_source_bind_p(), gsi_stmt(), NULL_TREE, and TREE_CODE.
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Register NEW_NAME to be the new reaching definition for all the names in OLD_NAMES. Used by the incremental SSA update routines to replace old SSA names with new ones.
References dump_file, print_gimple_stmt(), and TDF_SLIM.
Referenced by register_new_update_single().
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Register NEW_NAME to be the new reaching definition for OLD_NAME.
Push the current reaching definition into BLOCK_DEFS_STACK. This stack is later used by the dominator tree callbacks to restore the reaching definitions for all the variables defined in the block after a recursive visit to all its immediately dominated blocks.
Set the current reaching definition for OLD_NAME to be NEW_NAME.
References is_new_name(), is_old_name(), names_replaced_by(), and register_new_update_set().
| void release_ssa_name_after_update_ssa | ( | ) |
Mark NAME to be released after update_ssa has finished.
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SSA Rewriting Step 3. Visit all the successor blocks of BB looking for PHI nodes. For every PHI node found, add a new argument containing the current reaching definition for the variable and the edge through which that definition is reaching the PHI node.
Virtual operand PHI args do not need a location.
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Rewrite the actual blocks, statements, and PHI arguments, to be in SSA form.
ENTRY indicates the block where to start. Every block dominated by ENTRY will be rewritten.
WHAT indicates what actions will be taken by the renamer (see enum rewrite_mode).
BLOCKS are the set of interesting blocks for the dominator walker to process. If this set is NULL, then all the nodes dominated by ENTRY are walked. Otherwise, blocks dominated by ENTRY that are not present in BLOCKS are ignored.
Rewrite all the basic blocks in the program.
Recursively walk the dominator tree rewriting each statement in each basic block.
Debugging dumps.
References opt_pass::execute(), opt_pass::gate(), gate_into_ssa(), gimple_opt_pass::gimple_opt_pass(), and rewrite_into_ssa().
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Helper function for rewrite_stmt. Rewrite uses in a debug stmt.
Search a few source bind stmts at the start of first bb to
see if a DEBUG_EXPR_DECL can't be reused.
If not, add a new source bind stmt.
Check if info->current_def can be trusted.
If definition is in current bb, it is fine.
If definition bb doesn't dominate the current bb,
it can't be used. If there is just one definition and dominates the current
bb, it is fine. If there are some non-debug uses in the current bb,
it is fine. Otherwise give up for now.
References DECL_P, FOR_EACH_SSA_USE_OPERAND, gcc_checking_assert, get_reaching_def(), is_gimple_debug(), SET_USE, SSA_OP_ALL_USES, and USE_FROM_PTR.
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Main entry point into the SSA builder. The renaming process proceeds in four main phases:
1- Compute dominance frontier and immediate dominators, needed to insert PHI nodes and rename the function in dominator tree order.
2- Find and mark all the blocks that define variables.
3- Insert PHI nodes at dominance frontiers (insert_phi_nodes).
4- Rename all the blocks (rewrite_blocks) and statements in the program.
Steps 3 and 4 are done using the dominator tree walker (walk_dominator_tree).
Initialize operand data structures.
Initialize internal data needed by the renamer.
Initialize the set of interesting blocks. The callback mark_def_sites will add to this set those blocks that the renamer should process.
Initialize dominance frontier.
1- Compute dominance frontiers.
2- Find and mark definition sites.
3- Insert PHI nodes at dominance frontiers of definition blocks.
4- Rename all the blocks.
Free allocated memory.
Try to get rid of all gimplifier generated temporaries by making its SSA names anonymous. This way we can garbage collect them all after removing unused locals which we do in our TODO.
Referenced by rewrite_blocks().
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SSA Rewriting Step 2. Rewrite every variable used in each statement in the block with its immediate reaching definitions. Update the current definition of a variable when a new real or virtual definition is found.
If mark_def_sites decided that we don't need to rewrite this statement, ignore it.
Step 1. Rewrite USES in the statement.
Step 2. Register the statement's DEF operands.
If we rewrite a DECL into SSA form then drop its
clobber stmts and replace uses with a new default def.
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Visit all the successor blocks of BB looking for PHI nodes. For every PHI node found, check if any of its arguments is in OLD_SSA_NAMES. If so, and if the argument has a current reaching definition, replace it.
When updating a PHI node for a recently introduced symbol we may find NULL arguments. That's why we take the symbol from the LHS of the PHI node.
Update the argument if there is a reaching def.
Virtual operands do not need a location. Single element PHI nodes behave like copies, so get the
location from the phi argument.
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Update every variable used in the statement pointed-to by SI. The statement is assumed to be in SSA form already. Names in OLD_SSA_NAMES used by SI will be updated to their current reaching definition. Names in OLD_SSA_NAMES or NEW_SSA_NAMES defined by SI will be registered as a new definition for their corresponding name in OLD_SSA_NAMES.
Only update marked statements.
Rewrite USES included in OLD_SSA_NAMES and USES whose underlying symbol is marked for renaming.
DOM sometimes threads jumps in such a way that a
debug stmt ends up referencing a SSA variable that no
longer dominates the debug stmt, but such that all
incoming definitions refer to the same definition in
an earlier dominator. We could try to recover that
definition somehow, but this will have to do for now.
Introducing a default definition, which is what
maybe_replace_use() would do in such cases, may
modify code generation, for the otherwise-unused
default definition would never go away, modifying SSA
version numbers all over. Register definitions of names in NEW_SSA_NAMES and OLD_SSA_NAMES. Also register definitions for names whose underlying symbol is marked for renaming.
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Return true if STMT needs to be rewritten. When renaming a subset of the variables, not all statements will be processed. This is decided in mark_def_sites.
Referenced by maybe_register_def().
| void set_current_def | ( | ) |
Sets current definition of VAR to DEF.
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Mark block BB as the definition site for variable VAR. PHI_P is true if VAR is defined by a PHI node.
Set the bit corresponding to the block where VAR is defined.
Keep track of whether or not we may need to insert PHI nodes. If we are in the UNKNOWN state, then this is the first definition of VAR. Additionally, we have not seen any uses of VAR yet, so we do not need a PHI node for this variable at this time (i.e., transition to NEED_PHI_STATE_NO). If we are in any other state, then we either have multiple definitions of this variable occurring in different blocks or we saw a use of the variable which was not dominated by the block containing the definition(s). In this case we may need a PHI node, so enter state NEED_PHI_STATE_MAYBE.
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Mark block BB as having VAR live at the entry to BB.
Set the bit corresponding to the block where VAR is live in.
Keep track of whether or not we may need to insert PHI nodes. If we reach here in NEED_PHI_STATE_NO, see if this use is dominated by the single block containing the definition(s) of this variable. If it is, then we remain in NEED_PHI_STATE_NO, otherwise we transition to NEED_PHI_STATE_MAYBE.
References BITMAP_ALLOC, bitmap_set_bit, get_ssa_name_ann(), ssa_name_info::repl_set, and SSA_NAME_VERSION.
Referenced by add_new_name_mapping().
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If REGISTER_DEFS_P is true, mark STMT to have its DEFs registered.
References DECL_UID, hash_table< Descriptor, Allocator >::find_slot_with_hash(), NULL, and var_info_d::var.
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Set the rewrite marker on STMT to the value given by REWRITE_P.
References ssa_name_info::age, current_info_for_ssa_name_age, ssa_name_info::info, and NEED_PHI_STATE_UNKNOWN.
Referenced by add_new_name_mapping().
| void update_ssa | ( | ) |
Given a set of newly created SSA names (NEW_SSA_NAMES) and a set of existing SSA names (OLD_SSA_NAMES), update the SSA form so that:
1- The names in OLD_SSA_NAMES dominated by the definitions of NEW_SSA_NAMES are all re-written to be reached by the appropriate definition from NEW_SSA_NAMES.
2- If needed, new PHI nodes are added to the iterated dominance frontier of the blocks where each of NEW_SSA_NAMES are defined.
The mapping between OLD_SSA_NAMES and NEW_SSA_NAMES is setup by calling create_new_def_for to create new defs for names that the caller wants to replace.
The caller cretaes the new names to be inserted and the names that need to be replaced by calling create_new_def_for for each old definition to be replaced. Note that the function assumes that the new defining statement has already been inserted in the IL.
For instance, given the following code:
1 L0: 2 x_1 = PHI (0, x_5) 3 if (x_1 < 10) 4 if (x_1 > 7) 5 y_2 = 0 6 else 7 y_3 = x_1 + x_7 8 endif 9 x_5 = x_1 + 1 10 goto L0; 11 endif
Suppose that we insert new names x_10 and x_11 (lines 4 and 8).
1 L0: 2 x_1 = PHI (0, x_5) 3 if (x_1 < 10) 4 x_10 = ... 5 if (x_1 > 7) 6 y_2 = 0 7 else 8 x_11 = ... 9 y_3 = x_1 + x_7 10 endif 11 x_5 = x_1 + 1 12 goto L0; 13 endif
We want to replace all the uses of x_1 with the new definitions of x_10 and x_11. Note that the only uses that should be replaced are those at lines 5, 9 and 11. Also, the use of x_7 at line 9 should not be replaced (this is why we cannot just mark symbol 'x' for renaming).
Additionally, we may need to insert a PHI node at line 11 because that is a merge point for x_10 and x_11. So the use of x_1 at line 11 will be replaced with the new PHI node. The insertion of PHI nodes is optional. They are not strictly necessary to preserve the SSA form, and depending on what the caller inserted, they may not even be useful for the optimizers. UPDATE_FLAGS controls various aspects of how update_ssa operates, see the documentation for TODO_update_ssa*.
Only one update flag should be set.
If we only need to update virtuals, remove all the mappings for
real names before proceeding. The caller is responsible for
having dealt with the name mappings before calling update_ssa. Ensure that the dominance information is up-to-date.
If there are names defined in the replacement table, prepare definition and use sites for all the names in NEW_SSA_NAMES and OLD_SSA_NAMES.
If all the names in NEW_SSA_NAMES had been marked for
removal, and there are no symbols to rename, then there's
nothing else to do. Next, determine the block at which to start the renaming process.
If we rename bare symbols initialize the mapping to
auxiliar info we need to keep track of. If we have to rename some symbols from scratch, we need to
start the process at the root of the CFG. FIXME, it should
be possible to determine the nearest block that had a
definition for each of the symbols that are marked for
updating. For now this seems more work than it's worth. Traverse the CFG looking for existing definitions and uses of
symbols in SSA operands. Mark interesting blocks and
statements and set local live-in information for the PHI
placement heuristics. Otherwise, the entry block to the region is the nearest
common dominator for the blocks in BLOCKS. If requested, insert PHI nodes at the iterated dominance frontier of every block, creating new definitions for names in OLD_SSA_NAMES and for symbols found.
If the caller requested PHI nodes to be added, compute
dominance frontiers. insert_update_phi_nodes_for will call add_new_name_mapping
when inserting new PHI nodes, so the set OLD_SSA_NAMES
will grow while we are traversing it (but it will not
gain any new members). Copy OLD_SSA_NAMES to a temporary
for traversal. Insertion of PHI nodes may have added blocks to the region.
We need to re-compute START_BB to include the newly added
blocks. Reset the current definition for name and symbol before renaming the sub-graph.
Now start the renaming process at START_BB.
Debugging dumps.
Free allocated memory.
Referenced by expand_omp_sections(), find_uses_to_rename(), scale_dominated_blocks_in_loop(), and sese_add_exit_phis_edge().
Variable Documentation
Stack of trees used to restore the global currdefs to its original state after completing rewriting of a block and its dominator children. Its elements have the following properties:
- An SSA_NAME (N) indicates that the current definition of the underlying variable should be set to the given SSA_NAME. If the symbol associated with the SSA_NAME is not a GIMPLE register, the next slot in the stack must be a _DECL node (SYM). In this case, the name N in the previous slot is the current reaching definition for SYM.
- A _DECL node indicates that the underlying variable has no current definition.
- A NULL node at the top entry is used to mark the last slot associated with the current block.
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The set of blocks affected by update_ssa.
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The bitmap of non-NULL elements of PHIS_TO_REWRITE.
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Referenced by set_rewrite_uses().
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Set of SSA names that have been marked to be released after they were registered in the replacement table. They will be finally released after we finish updating the SSA web.
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Set of new SSA names being added by update_ssa. Note that both NEW_SSA_NAMES and OLD_SSA_NAMES are dense bitmaps because most of the operations done on them are presence tests.
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Set of existing SSA names being replaced by update_ssa.
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vec of vec of PHIs to rewrite in a basic block. Element I corresponds the to basic block with index I. Allocated once per compilation, not released between different functions.
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The set of symbols we ought to re-write into SSA form in update_ssa.
The function the SSA updating data structures have been initialized for. NULL if they need to be initialized by create_new_def_for.
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Each entry in VAR_INFOS contains an element of type STRUCT VAR_INFO_D.
