- Generated by
1.8.1.1
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GCC Middle and Back End API Reference
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| static bool | df_in_progress = false |
| static bool | can_alter_cfg = false |
| static vec< rtx > | worklist |
| static sbitmap | marked |
| static bitmap_obstack | dce_blocks_bitmap_obstack |
| static bitmap_obstack | dce_tmp_bitmap_obstack |
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Return true if store to MEM, starting OFF bytes from stack pointer, is a call argument store, and clear corresponding bits from SP_BYTES bitmap if it is.
References bitmap_clear(), and HOST_WIDE_INT.
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Process basic block BB. Return true if the live_in set has changed. REDO_OUT is true if the info at the bottom of the block needs to be recalculated before starting. AU is the proper set of artificial uses. Track global substitution of uses of dead pseudos in debug insns using GLOBAL_DEBUG.
Need to redo the live_out set of this block if when one of
the succs of this block has had a change in it live in
set. The insn is needed if there is someone who uses the output.
No matter if the instruction is needed or not, we remove
any regno in the defs from the live set. On the other hand, we do not allow the dead uses to set
anything in local_live. Insert debug temps for dead REGs used in subsequent debug
insns. We may have to emit a debug temp even if the insn
was marked, in case the debug use was after the point of
death.
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Return true if INSN is a normal instruction that can be deleted by the DCE pass.
We cannot delete calls inside of the recursive dce because
this may cause basic blocks to be deleted and this messes up
the rest of the stack of optimization passes. We cannot delete pure or const sibling calls because it is
hard to see the result. We can delete dead const or pure calls as long as they do not
infinite loop. Don't delete jumps, notes and the like.
Don't delete insns that may throw if we cannot do so.
If INSN sets a global_reg, leave it untouched.
A CLOBBER of a dead pseudo register serves no purpose.
That is not necessarily true for hard registers until
after reload. Because of the way that use-def chains are built, it is not
possible to tell if the clobber is dead because it can
never be the target of a use-def chain.
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A subroutine for which BODY is part of the instruction being tested; either the top-level pattern, or an element of a PARALLEL. The instruction is known not to be a bare USE or CLOBBER.
The UNSPEC case was added here because the ia-64 claims that
USEs do not work after reload and generates UNSPECS rather
than USEs. Since dce is run after reload we need to avoid
deleting these even if they are dead. If it turns out that
USEs really do work after reload, the ia-64 should be
changed, and the UNSPEC case can be removed.
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Delete every instruction that hasn't been marked.
Always delete no-op moves.
Otherwise rely only on the DCE algorithm.
Beware that reaching a dbg counter limit here can result
in miscompiled file. This occurs when a group of insns
must be deleted together, typically because the kept insn
depends on the output from the deleted insn. Deleting
this insns in reverse order (both at the bb level and
when looking at the blocks) minimizes this, but does not
eliminate it, since it is possible for the using insn to
be top of a block and the producer to be at the bottom of
the block. However, in most cases this will only result
in an uninitialized use of an insn that is dead anyway.
However, there is one rare case that will cause a
miscompile: deletion of non-looping pure and constant
calls on a machine where ACCUMULATE_OUTGOING_ARGS is true.
In this case it is possible to remove the call, but leave
the argument pushes to the stack. Because of the changes
to the stack pointer, this will almost always lead to a
miscompile. Before we delete the insn we have to remove the REG_EQUAL notes
for the destination regs in order to avoid dangling notes. If a pure or const call is deleted, this may make the cfg
have unreachable blocks. We rememeber this and call
delete_unreachable_blocks at the end. Now delete the insn.
Deleted a pure or const call.
Referenced by fast_dce(), and init_dce().
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Perform fast DCE once initialization is done. If WORD_LEVEL is true, use the word level dce, otherwise do it at the pseudo level.
The set of blocks that have been seen on this iteration.
The set of blocks that need to have the out vectors reset because
the in of one of their successors has changed. These regs are considered always live so if they end up dying
because of some def, we need to bring the back again. Calling
df_simulate_fixup_sets has the disadvantage of calling
bb_has_eh_pred once per insn, so we cache the information
here. Be tricky about when we need to iterate the
analysis. We only have redo the analysis if the
bitmaps change at the top of a block that is the
entry to a loop. Turn off the RUN_DCE flag to prevent recursive calls to
dce. So something was deleted that requires a redo. Do it on
the cheap. We do not need to rescan any instructions. We only need
to redo the dataflow equations for the blocks that had a
change at the top of the block. Then we need to redo the
iteration.
References bitmap_clear(), delete_unmarked_insns(), df_analyze_problem(), df_clear_flags(), DF_LR_RUN_DCE, df_set_flags(), and prescan_insns_for_dce().
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Try to find all stack stores of CALL_INSN arguments if ACCUMULATE_OUTGOING_ARGS. If all stack stores have been found and it is therefore safe to eliminate the call, return true, otherwise return false. This function should be first called with DO_MARK false, and only when the CALL_INSN is actually going to be marked called again with DO_MARK true.
First determine the minimum and maximum offset from sp for
stored arguments. If not fast, use chains to see if addr wasn't set to
sp + offset. Set bits in SP_BYTES bitmap for bytes relative to sp + min_sp_off
which contain arguments. Checking has been done in the previous
loop. Walk backwards, looking for argument stores. The search stops
when seeing another call, sp adjustment or memory store other than
argument store.
References defs, HOST_WIDE_INT, df_link::next, df_link::ref, and rtx_equal_p().
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Referenced by run_word_dce().
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References bitmap_clear(), bitmap_copy(), dead_debug_local_init(), df_print_word_regset(), dump_file, basic_block_def::index, and basic_block_def::succs.
Referenced by rest_of_handle_ud_dce().
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Initialize global variables for a new DCE pass.
References delete_unmarked_insns(), df_remove_problem(), fini_dce(), mark_artificial_uses(), mark_reg_dependencies(), prescan_insns_for_dce(), and reset_unmarked_insns_debug_uses().
| rtl_opt_pass* make_pass_fast_rtl_dce | ( | ) |
| rtl_opt_pass* make_pass_ud_rtl_dce | ( | ) |
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UD-based DSE routines.
Mark instructions that define artificially-used registers, such as the frame pointer and the stack pointer.
References bitmap_obstack_initialize(), can_alter_cfg, df_analyze(), df_chain_add_problem(), df_dump(), df_in_progress, DF_RD_PRUNE_DEAD_DEFS, df_set_flags(), DF_UD_CHAIN, and dump_file.
Referenced by init_dce().
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If INSN has not yet been marked as needed, mark it now, and add it to the worklist.
Referenced by prescan_insns_for_dce().
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Mark INSN if BODY stores to a non-register destination.
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A note_stores callback used by mark_nonreg_stores. DATA is the instruction containing DEST.
References mark_nonreg_stores_2(), and note_stores().
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A note_stores callback used by mark_nonreg_stores. DATA is the instruction containing DEST.
References bitmap_clear_bit(), and HOST_WIDE_INT.
Referenced by mark_nonreg_stores_1().
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Mark every instruction that defines a register value that INSN uses.
Referenced by init_dce().
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Return true if INSN has been marked as needed.
Artificial defs are always needed and they do not have an insn.
We should never see them here.
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Go through the instructions and mark those whose necessity is not dependent on inter-instruction information. Make sure all other instructions are not marked.
Don't mark argument stores now. They will be marked
if needed when the associated CALL is marked. find_call_stack_args only looks at argument stores in the
same bb.
References defs, df_get_artificial_uses(), basic_block_def::index, mark_insn(), df_link::next, and df_link::ref.
Referenced by fast_dce(), and init_dce().
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Remove all REG_EQUAL and REG_EQUIV notes referring to the registers INSN writes to.
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Scan all BBs for debug insns and reset those that reference values defined in unmarked insns.
??? FIXME could we propagate the values assigned to
each of the DEFs?
Referenced by init_dce().
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Fast register level DCE.
Referenced by run_word_dce().
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UD-chain based DCE.
Before any insns are deleted, we must remove the chains since
they are not bidirectional.
References execute(), and gate_ud_dce().
| void run_fast_dce | ( | void | ) |
Run a fast DCE pass.
| void run_fast_df_dce | ( | void | ) |
This is an internal call that is used by the df live register problem to run fast dce as a side effect of creating the live information. The stack is organized so that the lr problem is run, this pass is run, which updates the live info and the df scanning info, and then returns to allow the rest of the problems to be run. This can be called by elsewhere but it will not update the bit vectors for any other problems than LR.
If dce is able to delete something, it has to happen
immediately. Otherwise there will be problems handling the
eq_notes.
Referenced by df_lr_init().
| void run_word_dce | ( | void | ) |
Fast byte level DCE.
References execute(), gate_fast_dce(), and rest_of_handle_fast_dce().
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------------------------------------------------------------------------- Fast DCE functions -------------------------------------------------------------------------
Process basic block BB. Return true if the live_in set has changed. REDO_OUT is true if the info at the bottom of the block needs to be recalculated before starting. AU is the proper set of artificial uses. Track global substitution of uses of dead pseudos in debug insns using GLOBAL_DEBUG.
Need to redo the live_out set of this block if when one of
the succs of this block has had a change in it live in
set. No matter if the instruction is needed or not, we remove
any regno in the defs from the live set. On the other hand, we do not allow the dead uses to set
anything in local_live. Insert debug temps for dead REGs used in subsequent debug
insns. We may have to emit a debug temp even if the insn
was marked, in case the debug use was after the point of
death.
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True if we are allowed to alter the CFG in this pass.
Referenced by mark_artificial_uses().
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Bitmap obstacks used for block processing by the fast algorithm.
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@verbatim
RTL dead code elimination. Copyright (C) 2005-2013 Free Software Foundation, Inc.
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/.
------------------------------------------------------------------------- Core mark/delete routines -------------------------------------------------------------------------
True if we are invoked while the df engine is running; in this case, we don't want to reenter it.
Referenced by mark_artificial_uses().
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Bitmap of instructions marked as needed indexed by INSN_UID.
Instructions that have been marked but whose dependencies have not yet been processed.
Referenced by compute_available(), do_partial_partial_insertion(), dump_split_point(), find_src_set_src(), replace_pseudos_in(), and tm_memopt_accumulate_memops().
1.8.1.1