/* RTL-based forward propagation pass for GNU compiler. Copyright (C) 2005, 2006, 2007 Free Software Foundation, Inc. Contributed by Paolo Bonzini and Steven Bosscher. 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 . */ #include "config.h" #include "system.h" #include "coretypes.h" #include "tm.h" #include "toplev.h" #include "timevar.h" #include "rtl.h" #include "tm_p.h" #include "emit-rtl.h" #include "insn-config.h" #include "recog.h" #include "flags.h" #include "obstack.h" #include "basic-block.h" #include "output.h" #include "df.h" #include "target.h" #include "cfgloop.h" #include "tree-pass.h" /* This pass does simple forward propagation and simplification when an operand of an insn can only come from a single def. This pass uses df.c, so it is global. However, we only do limited analysis of available expressions. 1) The pass tries to propagate the source of the def into the use, and checks if the result is independent of the substituted value. For example, the high word of a (zero_extend:DI (reg:SI M)) is always zero, independent of the source register. In particular, we propagate constants into the use site. Sometimes RTL expansion did not put the constant in the same insn on purpose, to satisfy a predicate, and the result will fail to be recognized; but this happens rarely and in this case we can still create a REG_EQUAL note. For multi-word operations, this (set (subreg:SI (reg:DI 120) 0) (const_int 0)) (set (subreg:SI (reg:DI 120) 4) (const_int -1)) (set (subreg:SI (reg:DI 122) 0) (ior:SI (subreg:SI (reg:DI 119) 0) (subreg:SI (reg:DI 120) 0))) (set (subreg:SI (reg:DI 122) 4) (ior:SI (subreg:SI (reg:DI 119) 4) (subreg:SI (reg:DI 120) 4))) can be simplified to the much simpler (set (subreg:SI (reg:DI 122) 0) (subreg:SI (reg:DI 119))) (set (subreg:SI (reg:DI 122) 4) (const_int -1)) This particular propagation is also effective at putting together complex addressing modes. We are more aggressive inside MEMs, in that all definitions are propagated if the use is in a MEM; if the result is a valid memory address we check address_cost to decide whether the substitution is worthwhile. 2) The pass propagates register copies. This is not as effective as the copy propagation done by CSE's canon_reg, which works by walking the instruction chain, it can help the other transformations. We should consider removing this optimization, and instead reorder the RTL passes, because GCSE does this transformation too. With some luck, the CSE pass at the end of rest_of_handle_gcse could also go away. 3) The pass looks for paradoxical subregs that are actually unnecessary. Things like this: (set (reg:QI 120) (subreg:QI (reg:SI 118) 0)) (set (reg:QI 121) (subreg:QI (reg:SI 119) 0)) (set (reg:SI 122) (plus:SI (subreg:SI (reg:QI 120) 0) (subreg:SI (reg:QI 121) 0))) are very common on machines that can only do word-sized operations. For each use of a paradoxical subreg (subreg:WIDER (reg:NARROW N) 0), if it has a single def and it is (subreg:NARROW (reg:WIDE M) 0), we can replace the paradoxical subreg with simply (reg:WIDE M). The above will simplify this to (set (reg:QI 120) (subreg:QI (reg:SI 118) 0)) (set (reg:QI 121) (subreg:QI (reg:SI 119) 0)) (set (reg:SI 122) (plus:SI (reg:SI 118) (reg:SI 119))) where the first two insns are now dead. */ static int num_changes; /* Do not try to replace constant addresses or addresses of local and argument slots. These MEM expressions are made only once and inserted in many instructions, as well as being used to control symbol table output. It is not safe to clobber them. There are some uncommon cases where the address is already in a register for some reason, but we cannot take advantage of that because we have no easy way to unshare the MEM. In addition, looking up all stack addresses is costly. */ static bool can_simplify_addr (rtx addr) { rtx reg; if (CONSTANT_ADDRESS_P (addr)) return false; if (GET_CODE (addr) == PLUS) reg = XEXP (addr, 0); else reg = addr; return (!REG_P (reg) || (REGNO (reg) != FRAME_POINTER_REGNUM && REGNO (reg) != HARD_FRAME_POINTER_REGNUM && REGNO (reg) != ARG_POINTER_REGNUM)); } /* Returns a canonical version of X for the address, from the point of view, that all multiplications are represented as MULT instead of the multiply by a power of 2 being represented as ASHIFT. Every ASHIFT we find has been made by simplify_gen_binary and was not there before, so it is not shared. So we can do this in place. */ static void canonicalize_address (rtx x) { for (;;) switch (GET_CODE (x)) { case ASHIFT: if (GET_CODE (XEXP (x, 1)) == CONST_INT && INTVAL (XEXP (x, 1)) < GET_MODE_BITSIZE (GET_MODE (x)) && INTVAL (XEXP (x, 1)) >= 0) { HOST_WIDE_INT shift = INTVAL (XEXP (x, 1)); PUT_CODE (x, MULT); XEXP (x, 1) = gen_int_mode ((HOST_WIDE_INT) 1 << shift, GET_MODE (x)); } x = XEXP (x, 0); break; case PLUS: if (GET_CODE (XEXP (x, 0)) == PLUS || GET_CODE (XEXP (x, 0)) == ASHIFT || GET_CODE (XEXP (x, 0)) == CONST) canonicalize_address (XEXP (x, 0)); x = XEXP (x, 1); break; case CONST: x = XEXP (x, 0); break; default: return; } } /* OLD is a memory address. Return whether it is good to use NEW instead, for a memory access in the given MODE. */ static bool should_replace_address (rtx old, rtx new, enum machine_mode mode) { int gain; if (rtx_equal_p (old, new) || !memory_address_p (mode, new)) return false; /* Copy propagation is always ok. */ if (REG_P (old) && REG_P (new)) return true; /* Prefer the new address if it is less expensive. */ gain = address_cost (old, mode) - address_cost (new, mode); /* If the addresses have equivalent cost, prefer the new address if it has the highest `rtx_cost'. That has the potential of eliminating the most insns without additional costs, and it is the same that cse.c used to do. */ if (gain == 0) gain = rtx_cost (new, SET) - rtx_cost (old, SET); return (gain > 0); } /* Replace all occurrences of OLD in *PX with NEW and try to simplify the resulting expression. Replace *PX with a new RTL expression if an occurrence of OLD was found. If CAN_APPEAR is true, we always return true; if it is false, we can return false if, for at least one occurrence OLD, we failed to collapse the result to a constant. For example, (mult:M (reg:M A) (minus:M (reg:M B) (reg:M A))) may collapse to zero if replacing (reg:M B) with (reg:M A). CAN_APPEAR is disregarded inside MEMs: in that case, we always return true if the simplification is a cheaper and valid memory address. This is only a wrapper around simplify-rtx.c: do not add any pattern matching code here. (The sole exception is the handling of LO_SUM, but that is because there is no simplify_gen_* function for LO_SUM). */ static bool propagate_rtx_1 (rtx *px, rtx old, rtx new, bool can_appear) { rtx x = *px, tem = NULL_RTX, op0, op1, op2; enum rtx_code code = GET_CODE (x); enum machine_mode mode = GET_MODE (x); enum machine_mode op_mode; bool valid_ops = true; /* If X is OLD_RTX, return NEW_RTX. Otherwise, if this is an expression, try to build a new expression from recursive substitution. */ if (x == old) { *px = new; return can_appear; } switch (GET_RTX_CLASS (code)) { case RTX_UNARY: op0 = XEXP (x, 0); op_mode = GET_MODE (op0); valid_ops &= propagate_rtx_1 (&op0, old, new, can_appear); if (op0 == XEXP (x, 0)) return true; tem = simplify_gen_unary (code, mode, op0, op_mode); break; case RTX_BIN_ARITH: case RTX_COMM_ARITH: op0 = XEXP (x, 0); op1 = XEXP (x, 1); valid_ops &= propagate_rtx_1 (&op0, old, new, can_appear); valid_ops &= propagate_rtx_1 (&op1, old, new, can_appear); if (op0 == XEXP (x, 0) && op1 == XEXP (x, 1)) return true; tem = simplify_gen_binary (code, mode, op0, op1); break; case RTX_COMPARE: case RTX_COMM_COMPARE: op0 = XEXP (x, 0); op1 = XEXP (x, 1); op_mode = GET_MODE (op0) != VOIDmode ? GET_MODE (op0) : GET_MODE (op1); valid_ops &= propagate_rtx_1 (&op0, old, new, can_appear); valid_ops &= propagate_rtx_1 (&op1, old, new, can_appear); if (op0 == XEXP (x, 0) && op1 == XEXP (x, 1)) return true; tem = simplify_gen_relational (code, mode, op_mode, op0, op1); break; case RTX_TERNARY: case RTX_BITFIELD_OPS: op0 = XEXP (x, 0); op1 = XEXP (x, 1); op2 = XEXP (x, 2); op_mode = GET_MODE (op0); valid_ops &= propagate_rtx_1 (&op0, old, new, can_appear); valid_ops &= propagate_rtx_1 (&op1, old, new, can_appear); valid_ops &= propagate_rtx_1 (&op2, old, new, can_appear); if (op0 == XEXP (x, 0) && op1 == XEXP (x, 1) && op2 == XEXP (x, 2)) return true; if (op_mode == VOIDmode) op_mode = GET_MODE (op0); tem = simplify_gen_ternary (code, mode, op_mode, op0, op1, op2); break; case RTX_EXTRA: /* The only case we try to handle is a SUBREG. */ if (code == SUBREG) { op0 = XEXP (x, 0); valid_ops &= propagate_rtx_1 (&op0, old, new, can_appear); if (op0 == XEXP (x, 0)) return true; tem = simplify_gen_subreg (mode, op0, GET_MODE (SUBREG_REG (x)), SUBREG_BYTE (x)); } break; case RTX_OBJ: if (code == MEM && x != new) { rtx new_op0; op0 = XEXP (x, 0); /* There are some addresses that we cannot work on. */ if (!can_simplify_addr (op0)) return true; op0 = new_op0 = targetm.delegitimize_address (op0); valid_ops &= propagate_rtx_1 (&new_op0, old, new, true); /* Dismiss transformation that we do not want to carry on. */ if (!valid_ops || new_op0 == op0 || !(GET_MODE (new_op0) == GET_MODE (op0) || GET_MODE (new_op0) == VOIDmode)) return true; canonicalize_address (new_op0); /* Copy propagations are always ok. Otherwise check the costs. */ if (!(REG_P (old) && REG_P (new)) && !should_replace_address (op0, new_op0, GET_MODE (x))) return true; tem = replace_equiv_address_nv (x, new_op0); } else if (code == LO_SUM) { op0 = XEXP (x, 0); op1 = XEXP (x, 1); /* The only simplification we do attempts to remove references to op0 or make it constant -- in both cases, op0's invalidity will not make the result invalid. */ propagate_rtx_1 (&op0, old, new, true); valid_ops &= propagate_rtx_1 (&op1, old, new, can_appear); if (op0 == XEXP (x, 0) && op1 == XEXP (x, 1)) return true; /* (lo_sum (high x) x) -> x */ if (GET_CODE (op0) == HIGH && rtx_equal_p (XEXP (op0, 0), op1)) tem = op1; else tem = gen_rtx_LO_SUM (mode, op0, op1); /* OP1 is likely not a legitimate address, otherwise there would have been no LO_SUM. We want it to disappear if it is invalid, return false in that case. */ return memory_address_p (mode, tem); } else if (code == REG) { if (rtx_equal_p (x, old)) { *px = new; return can_appear; } } break; default: break; } /* No change, no trouble. */ if (tem == NULL_RTX) return true; *px = tem; /* The replacement we made so far is valid, if all of the recursive replacements were valid, or we could simplify everything to a constant. */ return valid_ops || can_appear || CONSTANT_P (tem); } /* Replace all occurrences of OLD in X with NEW and try to simplify the resulting expression (in mode MODE). Return a new expression if it is a constant, otherwise X. Simplifications where occurrences of NEW collapse to a constant are always accepted. All simplifications are accepted if NEW is a pseudo too. Otherwise, we accept simplifications that have a lower or equal cost. */ static rtx propagate_rtx (rtx x, enum machine_mode mode, rtx old, rtx new) { rtx tem; bool collapsed; if (REG_P (new) && REGNO (new) < FIRST_PSEUDO_REGISTER) return NULL_RTX; new = copy_rtx (new); tem = x; collapsed = propagate_rtx_1 (&tem, old, new, REG_P (new) || CONSTANT_P (new)); if (tem == x || !collapsed) return NULL_RTX; /* gen_lowpart_common will not be able to process VOIDmode entities other than CONST_INTs. */ if (GET_MODE (tem) == VOIDmode && GET_CODE (tem) != CONST_INT) return NULL_RTX; if (GET_MODE (tem) == VOIDmode) tem = rtl_hooks.gen_lowpart_no_emit (mode, tem); else gcc_assert (GET_MODE (tem) == mode); return tem; } /* Return true if the register from reference REF is killed between FROM to (but not including) TO. */ static bool local_ref_killed_between_p (struct df_ref * ref, rtx from, rtx to) { rtx insn; for (insn = from; insn != to; insn = NEXT_INSN (insn)) { struct df_ref **def_rec; if (!INSN_P (insn)) continue; for (def_rec = DF_INSN_DEFS (insn); *def_rec; def_rec++) { struct df_ref *def = *def_rec; if (DF_REF_REGNO (ref) == DF_REF_REGNO (def)) return true; } } return false; } /* Check if the given DEF is available in INSN. This would require full computation of available expressions; we check only restricted conditions: - if DEF is the sole definition of its register, go ahead; - in the same basic block, we check for no definitions killing the definition of DEF_INSN; - if USE's basic block has DEF's basic block as the sole predecessor, we check if the definition is killed after DEF_INSN or before TARGET_INSN insn, in their respective basic blocks. */ static bool use_killed_between (struct df_ref *use, rtx def_insn, rtx target_insn) { basic_block def_bb = BLOCK_FOR_INSN (def_insn); basic_block target_bb = BLOCK_FOR_INSN (target_insn); int regno; struct df_ref * def; /* In some obscure situations we can have a def reaching a use that is _before_ the def. In other words the def does not dominate the use even though the use and def are in the same basic block. This can happen when a register may be used uninitialized in a loop. In such cases, we must assume that DEF is not available. */ if (def_bb == target_bb ? DF_INSN_LUID (def_insn) >= DF_INSN_LUID (target_insn) : !dominated_by_p (CDI_DOMINATORS, target_bb, def_bb)) return true; /* Check if the reg in USE has only one definition. We already know that this definition reaches use, or we wouldn't be here. */ regno = DF_REF_REGNO (use); def = DF_REG_DEF_CHAIN (regno); if (def && (def->next_reg == NULL)) return false; /* Check locally if we are in the same basic block. */ if (def_bb == target_bb) return local_ref_killed_between_p (use, def_insn, target_insn); /* Finally, if DEF_BB is the sole predecessor of TARGET_BB. */ if (single_pred_p (target_bb) && single_pred (target_bb) == def_bb) { struct df_ref *x; /* See if USE is killed between DEF_INSN and the last insn in the basic block containing DEF_INSN. */ x = df_bb_regno_last_def_find (def_bb, regno); if (x && DF_INSN_LUID (x->insn) >= DF_INSN_LUID (def_insn)) return true; /* See if USE is killed between TARGET_INSN and the first insn in the basic block containing TARGET_INSN. */ x = df_bb_regno_first_def_find (target_bb, regno); if (x && DF_INSN_LUID (x->insn) < DF_INSN_LUID (target_insn)) return true; return false; } /* Otherwise assume the worst case. */ return true; } /* for_each_rtx traversal function that returns 1 if BODY points to a non-constant mem. */ static int varying_mem_p (rtx *body, void *data ATTRIBUTE_UNUSED) { rtx x = *body; return MEM_P (x) && !MEM_READONLY_P (x); } /* Check if all uses in DEF_INSN can be used in TARGET_INSN. This would require full computation of available expressions; we check only restricted conditions, see use_killed_between. */ static bool all_uses_available_at (rtx def_insn, rtx target_insn) { struct df_ref **use_rec; rtx def_set = single_set (def_insn); gcc_assert (def_set); /* If target_insn comes right after def_insn, which is very common for addresses, we can use a quicker test. */ if (NEXT_INSN (def_insn) == target_insn && REG_P (SET_DEST (def_set))) { rtx def_reg = SET_DEST (def_set); /* If the insn uses the reg that it defines, the substitution is invalid. */ for (use_rec = DF_INSN_USES (def_insn); *use_rec; use_rec++) { struct df_ref *use = *use_rec; if (rtx_equal_p (DF_REF_REG (use), def_reg)) return false; } for (use_rec = DF_INSN_EQ_USES (def_insn); *use_rec; use_rec++) { struct df_ref *use = *use_rec; if (rtx_equal_p (use->reg, def_reg)) return false; } } else { /* Look at all the uses of DEF_INSN, and see if they are not killed between DEF_INSN and TARGET_INSN. */ for (use_rec = DF_INSN_USES (def_insn); *use_rec; use_rec++) { struct df_ref *use = *use_rec; if (use_killed_between (use, def_insn, target_insn)) return false; } for (use_rec = DF_INSN_EQ_USES (def_insn); *use_rec; use_rec++) { struct df_ref *use = *use_rec; if (use_killed_between (use, def_insn, target_insn)) return false; } } /* We don't do any analysis of memories or aliasing. Reject any instruction that involves references to non-constant memory. */ return !for_each_rtx (&SET_SRC (def_set), varying_mem_p, NULL); } struct find_occurrence_data { rtx find; rtx *retval; }; /* Callback for for_each_rtx, used in find_occurrence. See if PX is the rtx we have to find. Return 1 to stop for_each_rtx if successful, or 0 to continue traversing otherwise. */ static int find_occurrence_callback (rtx *px, void *data) { struct find_occurrence_data *fod = (struct find_occurrence_data *) data; rtx x = *px; rtx find = fod->find; if (x == find) { fod->retval = px; return 1; } return 0; } /* Return a pointer to one of the occurrences of register FIND in *PX. */ static rtx * find_occurrence (rtx *px, rtx find) { struct find_occurrence_data data; gcc_assert (REG_P (find) || (GET_CODE (find) == SUBREG && REG_P (SUBREG_REG (find)))); data.find = find; data.retval = NULL; for_each_rtx (px, find_occurrence_callback, &data); return data.retval; } /* Inside INSN, the expression rooted at *LOC has been changed, moving some uses from USE_VEC. Find those that are present, and create new items in the data flow object of the pass. Mark any new uses as having the given TYPE. */ static void update_df (rtx insn, rtx *loc, struct df_ref **use_rec, enum df_ref_type type, int new_flags) { bool changed = false; /* Add a use for the registers that were propagated. */ while (*use_rec) { struct df_ref *use = *use_rec; struct df_ref *orig_use = use, *new_use; int width = -1; int offset = -1; rtx *new_loc = find_occurrence (loc, DF_REF_REG (orig_use)); use_rec++; if (!new_loc) continue; if (DF_REF_FLAGS_IS_SET (orig_use, DF_REF_SIGN_EXTRACT | DF_REF_ZERO_EXTRACT)) { width = DF_REF_WIDTH (orig_use); offset = DF_REF_OFFSET (orig_use); } /* Add a new insn use. Use the original type, because it says if the use was within a MEM. */ new_use = df_ref_create (DF_REF_REG (orig_use), new_loc, insn, BLOCK_FOR_INSN (insn), type, DF_REF_FLAGS (orig_use) | new_flags, width, offset); /* Set up the use-def chain. */ df_chain_copy (new_use, DF_REF_CHAIN (orig_use)); changed = true; } if (changed) df_insn_rescan (insn); } /* Try substituting NEW into LOC, which originated from forward propagation of USE's value from DEF_INSN. SET_REG_EQUAL says whether we are substituting the whole SET_SRC, so we can set a REG_EQUAL note if the new insn is not recognized. Return whether the substitution was performed. */ static bool try_fwprop_subst (struct df_ref *use, rtx *loc, rtx new, rtx def_insn, bool set_reg_equal) { rtx insn = DF_REF_INSN (use); enum df_ref_type type = DF_REF_TYPE (use); int flags = DF_REF_FLAGS (use); rtx set = single_set (insn); int old_cost = rtx_cost (SET_SRC (set), SET); bool ok; if (dump_file) { fprintf (dump_file, "\nIn insn %d, replacing\n ", INSN_UID (insn)); print_inline_rtx (dump_file, *loc, 2); fprintf (dump_file, "\n with "); print_inline_rtx (dump_file, new, 2); fprintf (dump_file, "\n"); } validate_unshare_change (insn, loc, new, true); if (!verify_changes (0)) { if (dump_file) fprintf (dump_file, "Changes to insn %d not recognized\n", INSN_UID (insn)); ok = false; } else if (DF_REF_TYPE (use) == DF_REF_REG_USE && rtx_cost (SET_SRC (set), SET) > old_cost) { if (dump_file) fprintf (dump_file, "Changes to insn %d not profitable\n", INSN_UID (insn)); ok = false; } else { if (dump_file) fprintf (dump_file, "Changed insn %d\n", INSN_UID (insn)); ok = true; } if (ok) { confirm_change_group (); num_changes++; df_ref_remove (use); if (!CONSTANT_P (new)) { update_df (insn, loc, DF_INSN_USES (def_insn), type, flags); update_df (insn, loc, DF_INSN_EQ_USES (def_insn), type, flags); } } else { cancel_changes (0); /* Can also record a simplified value in a REG_EQUAL note, making a new one if one does not already exist. Don't do this if the insn has a REG_RETVAL note, because the combined presence means that the REG_EQUAL note refers to the (full) contents of the libcall value. */ if (set_reg_equal && !find_reg_note (insn, REG_RETVAL, NULL_RTX)) { if (dump_file) fprintf (dump_file, " Setting REG_EQUAL note\n"); set_unique_reg_note (insn, REG_EQUAL, copy_rtx (new)); /* ??? Is this still necessary if we add the note through set_unique_reg_note? */ if (!CONSTANT_P (new)) { update_df (insn, loc, DF_INSN_USES (def_insn), type, DF_REF_IN_NOTE); update_df (insn, loc, DF_INSN_EQ_USES (def_insn), type, DF_REF_IN_NOTE); } } } return ok; } /* If USE is a paradoxical subreg, see if it can be replaced by a pseudo. */ static bool forward_propagate_subreg (struct df_ref *use, rtx def_insn, rtx def_set) { rtx use_reg = DF_REF_REG (use); rtx use_insn, src; /* Only consider paradoxical subregs... */ enum machine_mode use_mode = GET_MODE (use_reg); if (GET_CODE (use_reg) != SUBREG || !REG_P (SET_DEST (def_set)) || GET_MODE_SIZE (use_mode) <= GET_MODE_SIZE (GET_MODE (SUBREG_REG (use_reg)))) return false; /* If this is a paradoxical SUBREG, we have no idea what value the extra bits would have. However, if the operand is equivalent to a SUBREG whose operand is the same as our mode, and all the modes are within a word, we can just use the inner operand because these SUBREGs just say how to treat the register. */ use_insn = DF_REF_INSN (use); src = SET_SRC (def_set); if (GET_CODE (src) == SUBREG && REG_P (SUBREG_REG (src)) && GET_MODE (SUBREG_REG (src)) == use_mode && subreg_lowpart_p (src) && all_uses_available_at (def_insn, use_insn)) return try_fwprop_subst (use, DF_REF_LOC (use), SUBREG_REG (src), def_insn, false); else return false; } /* Try to replace USE with SRC (defined in DEF_INSN) and simplify the result. */ static bool forward_propagate_and_simplify (struct df_ref *use, rtx def_insn, rtx def_set) { rtx use_insn = DF_REF_INSN (use); rtx use_set = single_set (use_insn); rtx src, reg, new, *loc; bool set_reg_equal; enum machine_mode mode; if (!use_set) return false; /* Do not propagate into PC, CC0, etc. */ if (GET_MODE (SET_DEST (use_set)) == VOIDmode) return false; /* If def and use are subreg, check if they match. */ reg = DF_REF_REG (use); if (GET_CODE (reg) == SUBREG && GET_CODE (SET_DEST (def_set)) == SUBREG && (SUBREG_BYTE (SET_DEST (def_set)) != SUBREG_BYTE (reg) || GET_MODE (SET_DEST (def_set)) != GET_MODE (reg))) return false; /* Check if the def had a subreg, but the use has the whole reg. */ if (REG_P (reg) && GET_CODE (SET_DEST (def_set)) == SUBREG) return false; /* Check if the use has a subreg, but the def had the whole reg. Unlike the previous case, the optimization is possible and often useful indeed. */ if (GET_CODE (reg) == SUBREG && REG_P (SET_DEST (def_set))) reg = SUBREG_REG (reg); /* Check if the substitution is valid (last, because it's the most expensive check!). */ src = SET_SRC (def_set); if (!CONSTANT_P (src) && !all_uses_available_at (def_insn, use_insn)) return false; /* Check if the def is loading something from the constant pool; in this case we would undo optimization such as compress_float_constant. Still, we can set a REG_EQUAL note. */ if (MEM_P (src) && MEM_READONLY_P (src)) { rtx x = avoid_constant_pool_reference (src); if (x != src) { rtx note = find_reg_note (use_insn, REG_EQUAL, NULL_RTX); rtx old = note ? XEXP (note, 0) : SET_SRC (use_set); rtx new = simplify_replace_rtx (old, src, x); if (old != new) set_unique_reg_note (use_insn, REG_EQUAL, copy_rtx (new)); } return false; } /* Else try simplifying. */ if (DF_REF_TYPE (use) == DF_REF_REG_MEM_STORE) { loc = &SET_DEST (use_set); set_reg_equal = false; } else { rtx note = find_reg_note (use_insn, REG_EQUAL, NULL_RTX); if (DF_REF_FLAGS (use) & DF_REF_IN_NOTE) loc = &XEXP (note, 0); else loc = &SET_SRC (use_set); /* Do not replace an existing REG_EQUAL note if the insn is not recognized. Either we're already replacing in the note, or we'll separately try plugging the definition in the note and simplifying. */ set_reg_equal = (note == NULL_RTX); } if (GET_MODE (*loc) == VOIDmode) mode = GET_MODE (SET_DEST (use_set)); else mode = GET_MODE (*loc); new = propagate_rtx (*loc, mode, reg, src); if (!new) return false; return try_fwprop_subst (use, loc, new, def_insn, set_reg_equal); } /* Given a use USE of an insn, if it has a single reaching definition, try to forward propagate it into that insn. */ static void forward_propagate_into (struct df_ref *use) { struct df_link *defs; struct df_ref *def; rtx def_insn, def_set, use_insn; rtx parent; if (DF_REF_FLAGS (use) & DF_REF_READ_WRITE) return; if (DF_REF_IS_ARTIFICIAL (use)) return; /* Only consider uses that have a single definition. */ defs = DF_REF_CHAIN (use); if (!defs || defs->next) return; def = defs->ref; if (DF_REF_FLAGS (def) & DF_REF_READ_WRITE) return; if (DF_REF_IS_ARTIFICIAL (def)) return; /* Do not propagate loop invariant definitions inside the loop. */ if (DF_REF_BB (def)->loop_father != DF_REF_BB (use)->loop_father) return; /* Check if the use is still present in the insn! */ use_insn = DF_REF_INSN (use); if (DF_REF_FLAGS (use) & DF_REF_IN_NOTE) parent = find_reg_note (use_insn, REG_EQUAL, NULL_RTX); else parent = PATTERN (use_insn); if (!loc_mentioned_in_p (DF_REF_LOC (use), parent)) return; def_insn = DF_REF_INSN (def); if (multiple_sets (def_insn)) return; def_set = single_set (def_insn); if (!def_set) return; /* Only try one kind of propagation. If two are possible, we'll do it on the following iterations. */ if (!forward_propagate_and_simplify (use, def_insn, def_set)) forward_propagate_subreg (use, def_insn, def_set); } static void fwprop_init (void) { num_changes = 0; calculate_dominance_info (CDI_DOMINATORS); /* We do not always want to propagate into loops, so we have to find loops and be careful about them. But we have to call flow_loops_find before df_analyze, because flow_loops_find may introduce new jump insns (sadly) if we are not working in cfglayout mode. */ loop_optimizer_init (0); /* Now set up the dataflow problem (we only want use-def chains) and put the dataflow solver to work. */ df_set_flags (DF_EQ_NOTES); df_chain_add_problem (DF_UD_CHAIN); df_analyze (); df_maybe_reorganize_use_refs (DF_REF_ORDER_BY_INSN_WITH_NOTES); df_set_flags (DF_DEFER_INSN_RESCAN); } static void fwprop_done (void) { loop_optimizer_finalize (); free_dominance_info (CDI_DOMINATORS); cleanup_cfg (0); delete_trivially_dead_insns (get_insns (), max_reg_num ()); if (dump_file) fprintf (dump_file, "\nNumber of successful forward propagations: %d\n\n", num_changes); } /* Main entry point. */ static bool gate_fwprop (void) { return optimize > 0 && flag_forward_propagate; } static unsigned int fwprop (void) { unsigned i; fwprop_init (); /* Go through all the uses. update_df will create new ones at the end, and we'll go through them as well. Do not forward propagate addresses into loops until after unrolling. CSE did so because it was able to fix its own mess, but we are not. */ for (i = 0; i < DF_USES_TABLE_SIZE (); i++) { struct df_ref *use = DF_USES_GET (i); if (use) if (DF_REF_TYPE (use) == DF_REF_REG_USE || DF_REF_BB (use)->loop_father == NULL) forward_propagate_into (use); } fwprop_done (); return 0; } struct rtl_opt_pass pass_rtl_fwprop = { { RTL_PASS, "fwprop1", /* name */ gate_fwprop, /* gate */ fwprop, /* execute */ NULL, /* sub */ NULL, /* next */ 0, /* static_pass_number */ TV_FWPROP, /* tv_id */ 0, /* properties_required */ 0, /* properties_provided */ 0, /* properties_destroyed */ 0, /* todo_flags_start */ TODO_df_finish | TODO_verify_rtl_sharing | TODO_dump_func /* todo_flags_finish */ } }; static unsigned int fwprop_addr (void) { unsigned i; fwprop_init (); /* Go through all the uses. update_df will create new ones at the end, and we'll go through them as well. */ df_set_flags (DF_DEFER_INSN_RESCAN); for (i = 0; i < DF_USES_TABLE_SIZE (); i++) { struct df_ref *use = DF_USES_GET (i); if (use) if (DF_REF_TYPE (use) != DF_REF_REG_USE && DF_REF_BB (use)->loop_father != NULL) forward_propagate_into (use); } fwprop_done (); return 0; } struct rtl_opt_pass pass_rtl_fwprop_addr = { { RTL_PASS, "fwprop2", /* name */ gate_fwprop, /* gate */ fwprop_addr, /* execute */ NULL, /* sub */ NULL, /* next */ 0, /* static_pass_number */ TV_FWPROP, /* tv_id */ 0, /* properties_required */ 0, /* properties_provided */ 0, /* properties_destroyed */ 0, /* todo_flags_start */ TODO_df_finish | TODO_verify_rtl_sharing | TODO_dump_func /* todo_flags_finish */ } };