diff options
Diffstat (limited to 'gcc/cfgcleanup.c')
| -rw-r--r-- | gcc/cfgcleanup.c | 121 |
1 files changed, 121 insertions, 0 deletions
diff --git a/gcc/cfgcleanup.c b/gcc/cfgcleanup.c index 19583a78239..726c068eceb 100644 --- a/gcc/cfgcleanup.c +++ b/gcc/cfgcleanup.c @@ -2606,6 +2606,35 @@ trivially_empty_bb_p (basic_block bb) } } +/* Return true if BB contains just a return and possibly a USE of the + return value. Fill in *RET and *USE with the return and use insns + if any found, otherwise NULL. */ + +static bool +bb_is_just_return (basic_block bb, rtx_insn **ret, rtx_insn **use) +{ + *ret = *use = NULL; + rtx_insn *insn; + + if (bb == EXIT_BLOCK_PTR_FOR_FN (cfun)) + return false; + + FOR_BB_INSNS (bb, insn) + if (NONDEBUG_INSN_P (insn)) + { + if (!*ret && ANY_RETURN_P (PATTERN (insn))) + *ret = insn; + else if (!*ret && !*use && GET_CODE (PATTERN (insn)) == USE + && REG_P (XEXP (PATTERN (insn), 0)) + && REG_FUNCTION_VALUE_P (XEXP (PATTERN (insn), 0))) + *use = insn; + else + return false; + } + + return !!*ret; +} + /* Do simple CFG optimizations - basic block merging, simplifying of jump instructions etc. Return nonzero if changes were made. */ @@ -2792,6 +2821,98 @@ try_optimize_cfg (int mode) } } + /* Try to change a branch to a return to just that return. */ + rtx_insn *ret, *use; + if (single_succ_p (b) + && onlyjump_p (BB_END (b)) + && bb_is_just_return (single_succ (b), &ret, &use)) + { + if (redirect_jump (as_a <rtx_jump_insn *> (BB_END (b)), + PATTERN (ret), 0)) + { + if (use) + emit_insn_before (copy_insn (PATTERN (use)), + BB_END (b)); + if (dump_file) + fprintf (dump_file, "Changed jump %d->%d to return.\n", + b->index, single_succ (b)->index); + redirect_edge_succ (single_succ_edge (b), + EXIT_BLOCK_PTR_FOR_FN (cfun)); + single_succ_edge (b)->flags &= ~EDGE_CROSSING; + changed_here = true; + } + } + + /* Try to change a conditional branch to a return to the + respective conditional return. */ + if (EDGE_COUNT (b->succs) == 2 + && any_condjump_p (BB_END (b)) + && bb_is_just_return (BRANCH_EDGE (b)->dest, &ret, &use)) + { + if (redirect_jump (as_a <rtx_jump_insn *> (BB_END (b)), + PATTERN (ret), 0)) + { + if (use) + emit_insn_before (copy_insn (PATTERN (use)), + BB_END (b)); + if (dump_file) + fprintf (dump_file, "Changed conditional jump %d->%d " + "to conditional return.\n", + b->index, BRANCH_EDGE (b)->dest->index); + redirect_edge_succ (BRANCH_EDGE (b), + EXIT_BLOCK_PTR_FOR_FN (cfun)); + BRANCH_EDGE (b)->flags &= ~EDGE_CROSSING; + changed_here = true; + } + } + + /* Try to flip a conditional branch that falls through to + a return so that it becomes a conditional return and a + new jump to the original branch target. */ + if (EDGE_COUNT (b->succs) == 2 + && any_condjump_p (BB_END (b)) + && bb_is_just_return (FALLTHRU_EDGE (b)->dest, &ret, &use)) + { + if (invert_jump (as_a <rtx_jump_insn *> (BB_END (b)), + JUMP_LABEL (BB_END (b)), 0)) + { + basic_block new_ft = BRANCH_EDGE (b)->dest; + if (redirect_jump (as_a <rtx_jump_insn *> (BB_END (b)), + PATTERN (ret), 0)) + { + if (use) + emit_insn_before (copy_insn (PATTERN (use)), + BB_END (b)); + if (dump_file) + fprintf (dump_file, "Changed conditional jump " + "%d->%d to conditional return, adding " + "fall-through jump.\n", + b->index, BRANCH_EDGE (b)->dest->index); + redirect_edge_succ (BRANCH_EDGE (b), + EXIT_BLOCK_PTR_FOR_FN (cfun)); + BRANCH_EDGE (b)->flags &= ~EDGE_CROSSING; + std::swap (BRANCH_EDGE (b)->probability, + FALLTHRU_EDGE (b)->probability); + update_br_prob_note (b); + basic_block jb = force_nonfallthru (FALLTHRU_EDGE (b)); + notice_new_block (jb); + if (!redirect_jump (as_a <rtx_jump_insn *> (BB_END (jb)), + block_label (new_ft), 0)) + gcc_unreachable (); + redirect_edge_succ (single_succ_edge (jb), new_ft); + changed_here = true; + } + else + { + /* Invert the jump back to what it was. This should + never fail. */ + if (!invert_jump (as_a <rtx_jump_insn *> (BB_END (b)), + JUMP_LABEL (BB_END (b)), 0)) + gcc_unreachable (); + } + } + } + /* Simplify branch over branch. */ if ((mode & CLEANUP_EXPENSIVE) && !(mode & CLEANUP_CFGLAYOUT) |