From: Segher Boessenkool Date: Mon, 22 Oct 2018 20:23:39 +0000 (+0200) Subject: combine: Do not combine moves from hard registers X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=8d2d39587d941a40f25ea0144cceb677df115040;p=gcc.git combine: Do not combine moves from hard registers On most targets every function starts with moves from the parameter passing (hard) registers into pseudos. Similarly, after every call there is a move from the return register into a pseudo. These moves usually combine with later instructions (leaving pretty much the same instruction, just with a hard reg instead of a pseudo). This isn't a good idea. Register allocation can get rid of unnecessary moves just fine, and moving the parameter passing registers into many later instructions tends to prevent good register allocation. This patch disallows combining moves from a hard (non-fixed) register. This also avoid the problem mentioned in PR87600 #c3 (combining hard registers into inline assembler is problematic). Because the register move can often be combined with other instructions *itself*, for example for setting some condition code, this patch adds extra copies via new pseudos after every copy-from-hard-reg. On some targets this reduces average code size. On others it increases it a bit, 0.1% or 0.2% or so. (I tested this on all *-linux targets). PR rtl-optimization/87600 * combine.c: Add include of expr.h. (cant_combine_insn_p): Do not combine moves from any hard non-fixed register to a pseudo. (make_more_copies): New function, add a copy to a new pseudo after the moves from hard registers into pseudos. (rest_of_handle_combine): Declare rebuild_jump_labels_after_combine later. Call make_more_copies. From-SVN: r265398 --- diff --git a/gcc/ChangeLog b/gcc/ChangeLog index 6c051081971..1cfcc31b963 100644 --- a/gcc/ChangeLog +++ b/gcc/ChangeLog @@ -1,3 +1,14 @@ +2018-10-22 Segher Boessenkool + + PR rtl-optimization/87600 + * combine.c: Add include of expr.h. + (cant_combine_insn_p): Do not combine moves from any hard non-fixed + register to a pseudo. + (make_more_copies): New function, add a copy to a new pseudo after + the moves from hard registers into pseudos. + (rest_of_handle_combine): Declare rebuild_jump_labels_after_combine + later. Call make_more_copies. + 2018-10-22 Andrew Stubbs * lra-constraints.c (process_alt_operands): New local array, diff --git a/gcc/combine.c b/gcc/combine.c index 60cfe972aaf..8ec6809c05c 100644 --- a/gcc/combine.c +++ b/gcc/combine.c @@ -99,6 +99,7 @@ along with GCC; see the file COPYING3. If not see #include "explow.h" #include "insn-attr.h" #include "rtlhooks-def.h" +#include "expr.h" #include "params.h" #include "tree-pass.h" #include "valtrack.h" @@ -2348,8 +2349,7 @@ cant_combine_insn_p (rtx_insn *insn) dest = SUBREG_REG (dest); if (REG_P (src) && REG_P (dest) && ((HARD_REGISTER_P (src) - && ! TEST_HARD_REG_BIT (fixed_reg_set, REGNO (src)) - && targetm.class_likely_spilled_p (REGNO_REG_CLASS (REGNO (src)))) + && ! TEST_HARD_REG_BIT (fixed_reg_set, REGNO (src))) || (HARD_REGISTER_P (dest) && ! TEST_HARD_REG_BIT (fixed_reg_set, REGNO (dest)) && targetm.class_likely_spilled_p (REGNO_REG_CLASS (REGNO (dest)))))) @@ -14935,11 +14935,53 @@ dump_combine_total_stats (FILE *file) total_attempts, total_merges, total_extras, total_successes); } +/* Make pseudo-to-pseudo copies after every hard-reg-to-pseudo-copy, because + the reg-to-reg copy can usefully combine with later instructions, but we + do not want to combine the hard reg into later instructions, for that + restricts register allocation. */ +static void +make_more_copies (void) +{ + basic_block bb; + + FOR_EACH_BB_FN (bb, cfun) + { + rtx_insn *insn; + + FOR_BB_INSNS (bb, insn) + { + if (!NONDEBUG_INSN_P (insn)) + continue; + + rtx set = single_set (insn); + if (!set) + continue; + rtx src = SET_SRC (set); + rtx dest = SET_DEST (set); + if (GET_CODE (src) == SUBREG) + src = SUBREG_REG (src); + if (!(REG_P (src) && HARD_REGISTER_P (src))) + continue; + if (TEST_HARD_REG_BIT (fixed_reg_set, REGNO (src))) + continue; + + rtx new_reg = gen_reg_rtx (GET_MODE (dest)); + rtx_insn *insn1 = gen_move_insn (new_reg, src); + rtx_insn *insn2 = gen_move_insn (dest, new_reg); + emit_insn_after (insn1, insn); + emit_insn_after (insn2, insn1); + delete_insn (insn); + + insn = insn2; + } + } +} + /* Try combining insns through substitution. */ static unsigned int rest_of_handle_combine (void) { - int rebuild_jump_labels_after_combine; + make_more_copies (); df_set_flags (DF_LR_RUN_DCE + DF_DEFER_INSN_RESCAN); df_note_add_problem (); @@ -14948,7 +14990,7 @@ rest_of_handle_combine (void) regstat_init_n_sets_and_refs (); reg_n_sets_max = max_reg_num (); - rebuild_jump_labels_after_combine + int rebuild_jump_labels_after_combine = combine_instructions (get_insns (), max_reg_num ()); /* Combining insns may have turned an indirect jump into a