1 /* RTL-based forward propagation pass for GNU compiler.
2 Copyright (C) 2005, 2006, 2007 Free Software Foundation, Inc.
3 Contributed by Paolo Bonzini and Steven Bosscher.
5 This file is part of GCC.
7 GCC is free software; you can redistribute it and/or modify it under
8 the terms of the GNU General Public License as published by the Free
9 Software Foundation; either version 2, or (at your option) any later
12 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
13 WARRANTY; without even the implied warranty of MERCHANTABILITY or
14 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
17 You should have received a copy of the GNU General Public License
18 along with GCC; see the file COPYING. If not, write to the Free
19 Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA
24 #include "coretypes.h"
32 #include "insn-config.h"
36 #include "basic-block.h"
41 #include "tree-pass.h"
44 /* This pass does simple forward propagation and simplification when an
45 operand of an insn can only come from a single def. This pass uses
46 df.c, so it is global. However, we only do limited analysis of
47 available expressions.
49 1) The pass tries to propagate the source of the def into the use,
50 and checks if the result is independent of the substituted value.
51 For example, the high word of a (zero_extend:DI (reg:SI M)) is always
52 zero, independent of the source register.
54 In particular, we propagate constants into the use site. Sometimes
55 RTL expansion did not put the constant in the same insn on purpose,
56 to satisfy a predicate, and the result will fail to be recognized;
57 but this happens rarely and in this case we can still create a
58 REG_EQUAL note. For multi-word operations, this
60 (set (subreg:SI (reg:DI 120) 0) (const_int 0))
61 (set (subreg:SI (reg:DI 120) 4) (const_int -1))
62 (set (subreg:SI (reg:DI 122) 0)
63 (ior:SI (subreg:SI (reg:DI 119) 0) (subreg:SI (reg:DI 120) 0)))
64 (set (subreg:SI (reg:DI 122) 4)
65 (ior:SI (subreg:SI (reg:DI 119) 4) (subreg:SI (reg:DI 120) 4)))
67 can be simplified to the much simpler
69 (set (subreg:SI (reg:DI 122) 0) (subreg:SI (reg:DI 119)))
70 (set (subreg:SI (reg:DI 122) 4) (const_int -1))
72 This particular propagation is also effective at putting together
73 complex addressing modes. We are more aggressive inside MEMs, in
74 that all definitions are propagated if the use is in a MEM; if the
75 result is a valid memory address we check address_cost to decide
76 whether the substitution is worthwhile.
78 2) The pass propagates register copies. This is not as effective as
79 the copy propagation done by CSE's canon_reg, which works by walking
80 the instruction chain, it can help the other transformations.
82 We should consider removing this optimization, and instead reorder the
83 RTL passes, because GCSE does this transformation too. With some luck,
84 the CSE pass at the end of rest_of_handle_gcse could also go away.
86 3) The pass looks for paradoxical subregs that are actually unnecessary.
89 (set (reg:QI 120) (subreg:QI (reg:SI 118) 0))
90 (set (reg:QI 121) (subreg:QI (reg:SI 119) 0))
91 (set (reg:SI 122) (plus:SI (subreg:SI (reg:QI 120) 0)
92 (subreg:SI (reg:QI 121) 0)))
94 are very common on machines that can only do word-sized operations.
95 For each use of a paradoxical subreg (subreg:WIDER (reg:NARROW N) 0),
96 if it has a single def and it is (subreg:NARROW (reg:WIDE M) 0),
97 we can replace the paradoxical subreg with simply (reg:WIDE M). The
98 above will simplify this to
100 (set (reg:QI 120) (subreg:QI (reg:SI 118) 0))
101 (set (reg:QI 121) (subreg:QI (reg:SI 119) 0))
102 (set (reg:SI 122) (plus:SI (reg:SI 118) (reg:SI 119)))
104 where the first two insns are now dead. */
107 static int num_changes
;
110 /* Do not try to replace constant addresses or addresses of local and
111 argument slots. These MEM expressions are made only once and inserted
112 in many instructions, as well as being used to control symbol table
113 output. It is not safe to clobber them.
115 There are some uncommon cases where the address is already in a register
116 for some reason, but we cannot take advantage of that because we have
117 no easy way to unshare the MEM. In addition, looking up all stack
118 addresses is costly. */
121 can_simplify_addr (rtx addr
)
125 if (CONSTANT_ADDRESS_P (addr
))
128 if (GET_CODE (addr
) == PLUS
)
129 reg
= XEXP (addr
, 0);
134 || (REGNO (reg
) != FRAME_POINTER_REGNUM
135 && REGNO (reg
) != HARD_FRAME_POINTER_REGNUM
136 && REGNO (reg
) != ARG_POINTER_REGNUM
));
139 /* Returns a canonical version of X for the address, from the point of view,
140 that all multiplications are represented as MULT instead of the multiply
141 by a power of 2 being represented as ASHIFT.
143 Every ASHIFT we find has been made by simplify_gen_binary and was not
144 there before, so it is not shared. So we can do this in place. */
147 canonicalize_address (rtx x
)
150 switch (GET_CODE (x
))
153 if (GET_CODE (XEXP (x
, 1)) == CONST_INT
154 && INTVAL (XEXP (x
, 1)) < GET_MODE_BITSIZE (GET_MODE (x
))
155 && INTVAL (XEXP (x
, 1)) >= 0)
157 HOST_WIDE_INT shift
= INTVAL (XEXP (x
, 1));
159 XEXP (x
, 1) = gen_int_mode ((HOST_WIDE_INT
) 1 << shift
,
167 if (GET_CODE (XEXP (x
, 0)) == PLUS
168 || GET_CODE (XEXP (x
, 0)) == ASHIFT
169 || GET_CODE (XEXP (x
, 0)) == CONST
)
170 canonicalize_address (XEXP (x
, 0));
184 /* OLD is a memory address. Return whether it is good to use NEW instead,
185 for a memory access in the given MODE. */
188 should_replace_address (rtx old
, rtx
new, enum machine_mode mode
)
192 if (rtx_equal_p (old
, new) || !memory_address_p (mode
, new))
195 /* Copy propagation is always ok. */
196 if (REG_P (old
) && REG_P (new))
199 /* Prefer the new address if it is less expensive. */
200 gain
= address_cost (old
, mode
) - address_cost (new, mode
);
202 /* If the addresses have equivalent cost, prefer the new address
203 if it has the highest `rtx_cost'. That has the potential of
204 eliminating the most insns without additional costs, and it
205 is the same that cse.c used to do. */
207 gain
= rtx_cost (new, SET
) - rtx_cost (old
, SET
);
212 /* Replace all occurrences of OLD in *PX with NEW and try to simplify the
213 resulting expression. Replace *PX with a new RTL expression if an
214 occurrence of OLD was found.
216 If CAN_APPEAR is true, we always return true; if it is false, we
217 can return false if, for at least one occurrence OLD, we failed to
218 collapse the result to a constant. For example, (mult:M (reg:M A)
219 (minus:M (reg:M B) (reg:M A))) may collapse to zero if replacing
220 (reg:M B) with (reg:M A).
222 CAN_APPEAR is disregarded inside MEMs: in that case, we always return
223 true if the simplification is a cheaper and valid memory address.
225 This is only a wrapper around simplify-rtx.c: do not add any pattern
226 matching code here. (The sole exception is the handling of LO_SUM, but
227 that is because there is no simplify_gen_* function for LO_SUM). */
230 propagate_rtx_1 (rtx
*px
, rtx old
, rtx
new, bool can_appear
)
232 rtx x
= *px
, tem
= NULL_RTX
, op0
, op1
, op2
;
233 enum rtx_code code
= GET_CODE (x
);
234 enum machine_mode mode
= GET_MODE (x
);
235 enum machine_mode op_mode
;
236 bool valid_ops
= true;
238 /* If X is OLD_RTX, return NEW_RTX. Otherwise, if this is an expression,
239 try to build a new expression from recursive substitution. */
247 switch (GET_RTX_CLASS (code
))
251 op_mode
= GET_MODE (op0
);
252 valid_ops
&= propagate_rtx_1 (&op0
, old
, new, can_appear
);
253 if (op0
== XEXP (x
, 0))
255 tem
= simplify_gen_unary (code
, mode
, op0
, op_mode
);
262 valid_ops
&= propagate_rtx_1 (&op0
, old
, new, can_appear
);
263 valid_ops
&= propagate_rtx_1 (&op1
, old
, new, can_appear
);
264 if (op0
== XEXP (x
, 0) && op1
== XEXP (x
, 1))
266 tem
= simplify_gen_binary (code
, mode
, op0
, op1
);
270 case RTX_COMM_COMPARE
:
273 op_mode
= GET_MODE (op0
) != VOIDmode
? GET_MODE (op0
) : GET_MODE (op1
);
274 valid_ops
&= propagate_rtx_1 (&op0
, old
, new, can_appear
);
275 valid_ops
&= propagate_rtx_1 (&op1
, old
, new, can_appear
);
276 if (op0
== XEXP (x
, 0) && op1
== XEXP (x
, 1))
278 tem
= simplify_gen_relational (code
, mode
, op_mode
, op0
, op1
);
282 case RTX_BITFIELD_OPS
:
286 op_mode
= GET_MODE (op0
);
287 valid_ops
&= propagate_rtx_1 (&op0
, old
, new, can_appear
);
288 valid_ops
&= propagate_rtx_1 (&op1
, old
, new, can_appear
);
289 valid_ops
&= propagate_rtx_1 (&op2
, old
, new, can_appear
);
290 if (op0
== XEXP (x
, 0) && op1
== XEXP (x
, 1) && op2
== XEXP (x
, 2))
292 if (op_mode
== VOIDmode
)
293 op_mode
= GET_MODE (op0
);
294 tem
= simplify_gen_ternary (code
, mode
, op_mode
, op0
, op1
, op2
);
298 /* The only case we try to handle is a SUBREG. */
302 valid_ops
&= propagate_rtx_1 (&op0
, old
, new, can_appear
);
303 if (op0
== XEXP (x
, 0))
305 tem
= simplify_gen_subreg (mode
, op0
, GET_MODE (SUBREG_REG (x
)),
311 if (code
== MEM
&& x
!= new)
316 /* There are some addresses that we cannot work on. */
317 if (!can_simplify_addr (op0
))
320 op0
= new_op0
= targetm
.delegitimize_address (op0
);
321 valid_ops
&= propagate_rtx_1 (&new_op0
, old
, new, true);
323 /* Dismiss transformation that we do not want to carry on. */
326 || !(GET_MODE (new_op0
) == GET_MODE (op0
)
327 || GET_MODE (new_op0
) == VOIDmode
))
330 canonicalize_address (new_op0
);
332 /* Copy propagations are always ok. Otherwise check the costs. */
333 if (!(REG_P (old
) && REG_P (new))
334 && !should_replace_address (op0
, new_op0
, GET_MODE (x
)))
337 tem
= replace_equiv_address_nv (x
, new_op0
);
340 else if (code
== LO_SUM
)
345 /* The only simplification we do attempts to remove references to op0
346 or make it constant -- in both cases, op0's invalidity will not
347 make the result invalid. */
348 propagate_rtx_1 (&op0
, old
, new, true);
349 valid_ops
&= propagate_rtx_1 (&op1
, old
, new, can_appear
);
350 if (op0
== XEXP (x
, 0) && op1
== XEXP (x
, 1))
353 /* (lo_sum (high x) x) -> x */
354 if (GET_CODE (op0
) == HIGH
&& rtx_equal_p (XEXP (op0
, 0), op1
))
357 tem
= gen_rtx_LO_SUM (mode
, op0
, op1
);
359 /* OP1 is likely not a legitimate address, otherwise there would have
360 been no LO_SUM. We want it to disappear if it is invalid, return
361 false in that case. */
362 return memory_address_p (mode
, tem
);
365 else if (code
== REG
)
367 if (rtx_equal_p (x
, old
))
379 /* No change, no trouble. */
385 /* The replacement we made so far is valid, if all of the recursive
386 replacements were valid, or we could simplify everything to
388 return valid_ops
|| can_appear
|| CONSTANT_P (tem
);
391 /* Replace all occurrences of OLD in X with NEW and try to simplify the
392 resulting expression (in mode MODE). Return a new expression if it is
393 a constant, otherwise X.
395 Simplifications where occurrences of NEW collapse to a constant are always
396 accepted. All simplifications are accepted if NEW is a pseudo too.
397 Otherwise, we accept simplifications that have a lower or equal cost. */
400 propagate_rtx (rtx x
, enum machine_mode mode
, rtx old
, rtx
new)
405 if (REG_P (new) && REGNO (new) < FIRST_PSEUDO_REGISTER
)
408 new = copy_rtx (new);
411 collapsed
= propagate_rtx_1 (&tem
, old
, new, REG_P (new) || CONSTANT_P (new));
412 if (tem
== x
|| !collapsed
)
415 /* gen_lowpart_common will not be able to process VOIDmode entities other
417 if (GET_MODE (tem
) == VOIDmode
&& GET_CODE (tem
) != CONST_INT
)
420 if (GET_MODE (tem
) == VOIDmode
)
421 tem
= rtl_hooks
.gen_lowpart_no_emit (mode
, tem
);
423 gcc_assert (GET_MODE (tem
) == mode
);
431 /* Return true if the register from reference REF is killed
432 between FROM to (but not including) TO. */
435 local_ref_killed_between_p (struct df_ref
* ref
, rtx from
, rtx to
)
439 for (insn
= from
; insn
!= to
; insn
= NEXT_INSN (insn
))
441 struct df_ref
**def_rec
;
445 for (def_rec
= DF_INSN_DEFS (insn
); *def_rec
; def_rec
++)
447 struct df_ref
*def
= *def_rec
;
448 if (DF_REF_REGNO (ref
) == DF_REF_REGNO (def
))
456 /* Check if the given DEF is available in INSN. This would require full
457 computation of available expressions; we check only restricted conditions:
458 - if DEF is the sole definition of its register, go ahead;
459 - in the same basic block, we check for no definitions killing the
460 definition of DEF_INSN;
461 - if USE's basic block has DEF's basic block as the sole predecessor,
462 we check if the definition is killed after DEF_INSN or before
463 TARGET_INSN insn, in their respective basic blocks. */
465 use_killed_between (struct df_ref
*use
, rtx def_insn
, rtx target_insn
)
467 basic_block def_bb
= BLOCK_FOR_INSN (def_insn
);
468 basic_block target_bb
= BLOCK_FOR_INSN (target_insn
);
472 /* In some obscure situations we can have a def reaching a use
473 that is _before_ the def. In other words the def does not
474 dominate the use even though the use and def are in the same
475 basic block. This can happen when a register may be used
476 uninitialized in a loop. In such cases, we must assume that
477 DEF is not available. */
478 if (def_bb
== target_bb
479 ? DF_INSN_LUID (def_insn
) >= DF_INSN_LUID (target_insn
)
480 : !dominated_by_p (CDI_DOMINATORS
, target_bb
, def_bb
))
483 /* Check if the reg in USE has only one definition. We already
484 know that this definition reaches use, or we wouldn't be here. */
485 regno
= DF_REF_REGNO (use
);
486 def
= DF_REG_DEF_CHAIN (regno
);
487 if (def
&& (def
->next_reg
== NULL
))
490 /* Check locally if we are in the same basic block. */
491 if (def_bb
== target_bb
)
492 return local_ref_killed_between_p (use
, def_insn
, target_insn
);
494 /* Finally, if DEF_BB is the sole predecessor of TARGET_BB. */
495 if (single_pred_p (target_bb
)
496 && single_pred (target_bb
) == def_bb
)
500 /* See if USE is killed between DEF_INSN and the last insn in the
501 basic block containing DEF_INSN. */
502 x
= df_bb_regno_last_def_find (def_bb
, regno
);
503 if (x
&& DF_INSN_LUID (x
->insn
) >= DF_INSN_LUID (def_insn
))
506 /* See if USE is killed between TARGET_INSN and the first insn in the
507 basic block containing TARGET_INSN. */
508 x
= df_bb_regno_first_def_find (target_bb
, regno
);
509 if (x
&& DF_INSN_LUID (x
->insn
) < DF_INSN_LUID (target_insn
))
515 /* Otherwise assume the worst case. */
520 /* for_each_rtx traversal function that returns 1 if BODY points to
521 a non-constant mem. */
524 varying_mem_p (rtx
*body
, void *data ATTRIBUTE_UNUSED
)
527 return MEM_P (x
) && !MEM_READONLY_P (x
);
530 /* Check if all uses in DEF_INSN can be used in TARGET_INSN. This
531 would require full computation of available expressions;
532 we check only restricted conditions, see use_killed_between. */
534 all_uses_available_at (rtx def_insn
, rtx target_insn
)
536 struct df_ref
**use_rec
;
537 rtx def_set
= single_set (def_insn
);
539 gcc_assert (def_set
);
541 /* If target_insn comes right after def_insn, which is very common
542 for addresses, we can use a quicker test. */
543 if (NEXT_INSN (def_insn
) == target_insn
544 && REG_P (SET_DEST (def_set
)))
546 rtx def_reg
= SET_DEST (def_set
);
548 /* If the insn uses the reg that it defines, the substitution is
550 for (use_rec
= DF_INSN_USES (def_insn
); *use_rec
; use_rec
++)
552 struct df_ref
*use
= *use_rec
;
553 if (rtx_equal_p (DF_REF_REG (use
), def_reg
))
556 for (use_rec
= DF_INSN_EQ_USES (def_insn
); *use_rec
; use_rec
++)
558 struct df_ref
*use
= *use_rec
;
559 if (rtx_equal_p (use
->reg
, def_reg
))
565 /* Look at all the uses of DEF_INSN, and see if they are not
566 killed between DEF_INSN and TARGET_INSN. */
567 for (use_rec
= DF_INSN_USES (def_insn
); *use_rec
; use_rec
++)
569 struct df_ref
*use
= *use_rec
;
570 if (use_killed_between (use
, def_insn
, target_insn
))
573 for (use_rec
= DF_INSN_EQ_USES (def_insn
); *use_rec
; use_rec
++)
575 struct df_ref
*use
= *use_rec
;
576 if (use_killed_between (use
, def_insn
, target_insn
))
581 /* We don't do any analysis of memories or aliasing. Reject any
582 instruction that involves references to non-constant memory. */
583 return !for_each_rtx (&SET_SRC (def_set
), varying_mem_p
, NULL
);
587 struct find_occurrence_data
593 /* Callback for for_each_rtx, used in find_occurrence.
594 See if PX is the rtx we have to find. Return 1 to stop for_each_rtx
595 if successful, or 0 to continue traversing otherwise. */
598 find_occurrence_callback (rtx
*px
, void *data
)
600 struct find_occurrence_data
*fod
= (struct find_occurrence_data
*) data
;
602 rtx find
= fod
->find
;
613 /* Return a pointer to one of the occurrences of register FIND in *PX. */
616 find_occurrence (rtx
*px
, rtx find
)
618 struct find_occurrence_data data
;
620 gcc_assert (REG_P (find
)
621 || (GET_CODE (find
) == SUBREG
622 && REG_P (SUBREG_REG (find
))));
626 for_each_rtx (px
, find_occurrence_callback
, &data
);
631 /* Inside INSN, the expression rooted at *LOC has been changed, moving some
632 uses from USE_VEC. Find those that are present, and create new items
633 in the data flow object of the pass. Mark any new uses as having the
636 update_df (rtx insn
, rtx
*loc
, struct df_ref
**use_rec
, enum df_ref_type type
,
639 bool changed
= false;
641 /* Add a use for the registers that were propagated. */
644 struct df_ref
*use
= *use_rec
;
645 struct df_ref
*orig_use
= use
, *new_use
;
646 rtx
*new_loc
= find_occurrence (loc
, DF_REF_REG (orig_use
));
652 /* Add a new insn use. Use the original type, because it says if the
653 use was within a MEM. */
654 new_use
= df_ref_create (DF_REF_REG (orig_use
), new_loc
,
655 insn
, BLOCK_FOR_INSN (insn
),
656 type
, DF_REF_FLAGS (orig_use
) | new_flags
);
658 /* Set up the use-def chain. */
659 df_chain_copy (new_use
, DF_REF_CHAIN (orig_use
));
663 df_insn_rescan (insn
);
667 /* Try substituting NEW into LOC, which originated from forward propagation
668 of USE's value from DEF_INSN. SET_REG_EQUAL says whether we are
669 substituting the whole SET_SRC, so we can set a REG_EQUAL note if the
670 new insn is not recognized. Return whether the substitution was
674 try_fwprop_subst (struct df_ref
*use
, rtx
*loc
, rtx
new, rtx def_insn
, bool set_reg_equal
)
676 rtx insn
= DF_REF_INSN (use
);
677 enum df_ref_type type
= DF_REF_TYPE (use
);
678 int flags
= DF_REF_FLAGS (use
);
682 fprintf (dump_file
, "\nIn insn %d, replacing\n ", INSN_UID (insn
));
683 print_inline_rtx (dump_file
, *loc
, 2);
684 fprintf (dump_file
, "\n with ");
685 print_inline_rtx (dump_file
, new, 2);
686 fprintf (dump_file
, "\n");
689 if (validate_change (insn
, loc
, new, false))
693 fprintf (dump_file
, "Changed insn %d\n", INSN_UID (insn
));
696 if (!CONSTANT_P (new))
698 update_df (insn
, loc
, DF_INSN_USES (def_insn
), type
, flags
);
699 update_df (insn
, loc
, DF_INSN_EQ_USES (def_insn
), type
, flags
);
706 fprintf (dump_file
, "Changes to insn %d not recognized\n",
709 /* Can also record a simplified value in a REG_EQUAL note, making a
710 new one if one does not already exist. */
714 fprintf (dump_file
, " Setting REG_EQUAL note\n");
716 set_unique_reg_note (insn
, REG_EQUAL
, copy_rtx (new));
718 /* ??? Is this still necessary if we add the note through
719 set_unique_reg_note? */
720 if (!CONSTANT_P (new))
722 update_df (insn
, loc
, DF_INSN_USES (def_insn
),
723 type
, DF_REF_IN_NOTE
);
724 update_df (insn
, loc
, DF_INSN_EQ_USES (def_insn
),
725 type
, DF_REF_IN_NOTE
);
734 /* If USE is a paradoxical subreg, see if it can be replaced by a pseudo. */
737 forward_propagate_subreg (struct df_ref
*use
, rtx def_insn
, rtx def_set
)
739 rtx use_reg
= DF_REF_REG (use
);
742 /* Only consider paradoxical subregs... */
743 enum machine_mode use_mode
= GET_MODE (use_reg
);
744 if (GET_CODE (use_reg
) != SUBREG
745 || !REG_P (SET_DEST (def_set
))
746 || GET_MODE_SIZE (use_mode
)
747 <= GET_MODE_SIZE (GET_MODE (SUBREG_REG (use_reg
))))
750 /* If this is a paradoxical SUBREG, we have no idea what value the
751 extra bits would have. However, if the operand is equivalent to
752 a SUBREG whose operand is the same as our mode, and all the modes
753 are within a word, we can just use the inner operand because
754 these SUBREGs just say how to treat the register. */
755 use_insn
= DF_REF_INSN (use
);
756 src
= SET_SRC (def_set
);
757 if (GET_CODE (src
) == SUBREG
758 && REG_P (SUBREG_REG (src
))
759 && GET_MODE (SUBREG_REG (src
)) == use_mode
760 && subreg_lowpart_p (src
)
761 && all_uses_available_at (def_insn
, use_insn
))
762 return try_fwprop_subst (use
, DF_REF_LOC (use
), SUBREG_REG (src
),
768 /* Try to replace USE with SRC (defined in DEF_INSN) and simplify the
772 forward_propagate_and_simplify (struct df_ref
*use
, rtx def_insn
, rtx def_set
)
774 rtx use_insn
= DF_REF_INSN (use
);
775 rtx use_set
= single_set (use_insn
);
776 rtx src
, reg
, new, *loc
;
778 enum machine_mode mode
;
783 /* Do not propagate into PC, CC0, etc. */
784 if (GET_MODE (SET_DEST (use_set
)) == VOIDmode
)
787 /* If def and use are subreg, check if they match. */
788 reg
= DF_REF_REG (use
);
789 if (GET_CODE (reg
) == SUBREG
790 && GET_CODE (SET_DEST (def_set
)) == SUBREG
791 && (SUBREG_BYTE (SET_DEST (def_set
)) != SUBREG_BYTE (reg
)
792 || GET_MODE (SET_DEST (def_set
)) != GET_MODE (reg
)))
795 /* Check if the def had a subreg, but the use has the whole reg. */
796 if (REG_P (reg
) && GET_CODE (SET_DEST (def_set
)) == SUBREG
)
799 /* Check if the use has a subreg, but the def had the whole reg. Unlike the
800 previous case, the optimization is possible and often useful indeed. */
801 if (GET_CODE (reg
) == SUBREG
&& REG_P (SET_DEST (def_set
)))
802 reg
= SUBREG_REG (reg
);
804 /* Check if the substitution is valid (last, because it's the most
805 expensive check!). */
806 src
= SET_SRC (def_set
);
807 if (!CONSTANT_P (src
) && !all_uses_available_at (def_insn
, use_insn
))
810 /* Check if the def is loading something from the constant pool; in this
811 case we would undo optimization such as compress_float_constant.
812 Still, we can set a REG_EQUAL note. */
813 if (MEM_P (src
) && MEM_READONLY_P (src
))
815 rtx x
= avoid_constant_pool_reference (src
);
818 rtx note
= find_reg_note (use_insn
, REG_EQUAL
, NULL_RTX
);
819 rtx old
= note
? XEXP (note
, 0) : SET_SRC (use_set
);
820 rtx
new = simplify_replace_rtx (old
, src
, x
);
822 set_unique_reg_note (use_insn
, REG_EQUAL
, copy_rtx (new));
827 /* Else try simplifying. */
829 if (DF_REF_TYPE (use
) == DF_REF_REG_MEM_STORE
)
831 loc
= &SET_DEST (use_set
);
832 set_reg_equal
= false;
836 rtx note
= find_reg_note (use_insn
, REG_EQUAL
, NULL_RTX
);
837 if (DF_REF_FLAGS (use
) & DF_REF_IN_NOTE
)
838 loc
= &XEXP (note
, 0);
840 loc
= &SET_SRC (use_set
);
842 /* Do not replace an existing REG_EQUAL note if the insn is not
843 recognized. Either we're already replacing in the note, or
844 we'll separately try plugging the definition in the note and
846 set_reg_equal
= (note
== NULL_RTX
);
849 if (GET_MODE (*loc
) == VOIDmode
)
850 mode
= GET_MODE (SET_DEST (use_set
));
852 mode
= GET_MODE (*loc
);
854 new = propagate_rtx (*loc
, mode
, reg
, src
);
859 return try_fwprop_subst (use
, loc
, new, def_insn
, set_reg_equal
);
863 /* Given a use USE of an insn, if it has a single reaching
864 definition, try to forward propagate it into that insn. */
867 forward_propagate_into (struct df_ref
*use
)
869 struct df_link
*defs
;
871 rtx def_insn
, def_set
, use_insn
;
874 if (DF_REF_FLAGS (use
) & DF_REF_READ_WRITE
)
876 if (DF_REF_IS_ARTIFICIAL (use
))
879 /* Only consider uses that have a single definition. */
880 defs
= DF_REF_CHAIN (use
);
881 if (!defs
|| defs
->next
)
885 if (DF_REF_FLAGS (def
) & DF_REF_READ_WRITE
)
887 if (DF_REF_IS_ARTIFICIAL (def
))
890 /* Do not propagate loop invariant definitions inside the loop. */
891 if (DF_REF_BB (def
)->loop_father
!= DF_REF_BB (use
)->loop_father
)
894 /* Check if the use is still present in the insn! */
895 use_insn
= DF_REF_INSN (use
);
896 if (DF_REF_FLAGS (use
) & DF_REF_IN_NOTE
)
897 parent
= find_reg_note (use_insn
, REG_EQUAL
, NULL_RTX
);
899 parent
= PATTERN (use_insn
);
901 if (!loc_mentioned_in_p (DF_REF_LOC (use
), parent
))
904 def_insn
= DF_REF_INSN (def
);
905 if (multiple_sets (def_insn
))
907 def_set
= single_set (def_insn
);
911 /* Only try one kind of propagation. If two are possible, we'll
912 do it on the following iterations. */
913 if (!forward_propagate_and_simplify (use
, def_insn
, def_set
))
914 forward_propagate_subreg (use
, def_insn
, def_set
);
922 calculate_dominance_info (CDI_DOMINATORS
);
924 /* We do not always want to propagate into loops, so we have to find
925 loops and be careful about them. But we have to call flow_loops_find
926 before df_analyze, because flow_loops_find may introduce new jump
927 insns (sadly) if we are not working in cfglayout mode. */
928 loop_optimizer_init (0);
930 /* Now set up the dataflow problem (we only want use-def chains) and
931 put the dataflow solver to work. */
932 df_set_flags (DF_EQ_NOTES
);
933 df_chain_add_problem (DF_UD_CHAIN
);
935 df_maybe_reorganize_use_refs (DF_REF_ORDER_BY_INSN_WITH_NOTES
);
936 df_set_flags (DF_DEFER_INSN_RESCAN
);
942 loop_optimizer_finalize ();
944 free_dominance_info (CDI_DOMINATORS
);
946 delete_trivially_dead_insns (get_insns (), max_reg_num ());
950 "\nNumber of successful forward propagations: %d\n\n",
956 /* Main entry point. */
961 return optimize
> 0 && flag_forward_propagate
;
971 /* Go through all the uses. update_df will create new ones at the
972 end, and we'll go through them as well.
974 Do not forward propagate addresses into loops until after unrolling.
975 CSE did so because it was able to fix its own mess, but we are not. */
977 for (i
= 0; i
< DF_USES_TABLE_SIZE (); i
++)
979 struct df_ref
*use
= DF_USES_GET (i
);
981 if (DF_REF_TYPE (use
) == DF_REF_REG_USE
982 || DF_REF_BB (use
)->loop_father
== NULL
)
983 forward_propagate_into (use
);
990 struct tree_opt_pass pass_rtl_fwprop
=
992 "fwprop1", /* name */
993 gate_fwprop
, /* gate */
994 fwprop
, /* execute */
997 0, /* static_pass_number */
998 TV_FWPROP
, /* tv_id */
999 0, /* properties_required */
1000 0, /* properties_provided */
1001 0, /* properties_destroyed */
1002 0, /* todo_flags_start */
1004 TODO_dump_func
, /* todo_flags_finish */
1014 /* Go through all the uses. update_df will create new ones at the
1015 end, and we'll go through them as well. */
1016 df_set_flags (DF_DEFER_INSN_RESCAN
);
1018 for (i
= 0; i
< DF_USES_TABLE_SIZE (); i
++)
1020 struct df_ref
*use
= DF_USES_GET (i
);
1022 if (DF_REF_TYPE (use
) != DF_REF_REG_USE
1023 && DF_REF_BB (use
)->loop_father
!= NULL
)
1024 forward_propagate_into (use
);
1032 struct tree_opt_pass pass_rtl_fwprop_addr
=
1034 "fwprop2", /* name */
1035 gate_fwprop
, /* gate */
1036 fwprop_addr
, /* execute */
1039 0, /* static_pass_number */
1040 TV_FWPROP
, /* tv_id */
1041 0, /* properties_required */
1042 0, /* properties_provided */
1043 0, /* properties_destroyed */
1044 0, /* todo_flags_start */
1046 TODO_dump_func
, /* todo_flags_finish */