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From: Richard Sandiford <rsandifo@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org Subject: [gcc r14-4696] Handle epilogues that contain jumps Date: Tue, 17 Oct 2023 22:45:52 +0000 (GMT) [thread overview] Message-ID: <20231017224552.5D3413858D33@sourceware.org> (raw) https://gcc.gnu.org/g:aeb3f0436f8ae84e593eda9641fe4e6fdf0afb3e commit r14-4696-gaeb3f0436f8ae84e593eda9641fe4e6fdf0afb3e Author: Richard Sandiford <richard.sandiford@arm.com> Date: Tue Oct 17 23:45:43 2023 +0100 Handle epilogues that contain jumps The prologue/epilogue pass allows the prologue sequence to contain jumps. The sequence is then partitioned into basic blocks using find_many_sub_basic_blocks. This patch treats epilogues in a similar way. Since only one block might need to be split, the patch (re)introduces a find_sub_basic_blocks routine to handle a single block. The new routine hard-codes the assumption that split_block will chain the new block immediately after the original block. The routine doesn't try to replicate the fix for PR81030, since that was specific to gimple->rtl expansion. The patch is needed for follow-on aarch64 patches that add conditional code to the epilogue. The tests are part of those patches. gcc/ * cfgbuild.h (find_sub_basic_blocks): Declare. * cfgbuild.cc (update_profile_for_new_sub_basic_block): New function, split out from... (find_many_sub_basic_blocks): ...here. (find_sub_basic_blocks): New function. * function.cc (thread_prologue_and_epilogue_insns): Handle epilogues that contain jumps. Diff: --- gcc/cfgbuild.cc | 95 +++++++++++++++++++++++++++++++++++++++------------------ gcc/cfgbuild.h | 1 + gcc/function.cc | 4 +++ 3 files changed, 70 insertions(+), 30 deletions(-) diff --git a/gcc/cfgbuild.cc b/gcc/cfgbuild.cc index 15ed4deb5f7d..9a6b34fb4b1e 100644 --- a/gcc/cfgbuild.cc +++ b/gcc/cfgbuild.cc @@ -693,6 +693,43 @@ compute_outgoing_frequencies (basic_block b) } } +/* Update the profile information for BB, which was created by splitting + an RTL block that had a non-final jump. */ + +static void +update_profile_for_new_sub_basic_block (basic_block bb) +{ + edge e; + edge_iterator ei; + + bool initialized_src = false, uninitialized_src = false; + bb->count = profile_count::zero (); + FOR_EACH_EDGE (e, ei, bb->preds) + { + if (e->count ().initialized_p ()) + { + bb->count += e->count (); + initialized_src = true; + } + else + uninitialized_src = true; + } + /* When some edges are missing with read profile, this is + most likely because RTL expansion introduced loop. + When profile is guessed we may have BB that is reachable + from unlikely path as well as from normal path. + + TODO: We should handle loops created during BB expansion + correctly here. For now we assume all those loop to cycle + precisely once. */ + if (!initialized_src + || (uninitialized_src + && profile_status_for_fn (cfun) < PROFILE_GUESSED)) + bb->count = profile_count::uninitialized (); + + compute_outgoing_frequencies (bb); +} + /* Assume that some pass has inserted labels or control flow instructions within a basic block. Split basic blocks as needed and create edges. */ @@ -744,40 +781,15 @@ find_many_sub_basic_blocks (sbitmap blocks) if (profile_status_for_fn (cfun) != PROFILE_ABSENT) FOR_BB_BETWEEN (bb, min, max->next_bb, next_bb) { - edge e; - edge_iterator ei; - if (STATE (bb) == BLOCK_ORIGINAL) continue; if (STATE (bb) == BLOCK_NEW) { - bool initialized_src = false, uninitialized_src = false; - bb->count = profile_count::zero (); - FOR_EACH_EDGE (e, ei, bb->preds) - { - if (e->count ().initialized_p ()) - { - bb->count += e->count (); - initialized_src = true; - } - else - uninitialized_src = true; - } - /* When some edges are missing with read profile, this is - most likely because RTL expansion introduced loop. - When profile is guessed we may have BB that is reachable - from unlikely path as well as from normal path. - - TODO: We should handle loops created during BB expansion - correctly here. For now we assume all those loop to cycle - precisely once. */ - if (!initialized_src - || (uninitialized_src - && profile_status_for_fn (cfun) < PROFILE_GUESSED)) - bb->count = profile_count::uninitialized (); + update_profile_for_new_sub_basic_block (bb); + continue; } - /* If nothing changed, there is no need to create new BBs. */ - else if (EDGE_COUNT (bb->succs) == n_succs[bb->index]) + /* If nothing changed, there is no need to create new BBs. */ + if (EDGE_COUNT (bb->succs) == n_succs[bb->index]) { /* In rare occassions RTL expansion might have mistakely assigned a probabilities different from what is in CFG. This happens @@ -788,10 +800,33 @@ find_many_sub_basic_blocks (sbitmap blocks) update_br_prob_note (bb); continue; } - compute_outgoing_frequencies (bb); } FOR_EACH_BB_FN (bb, cfun) SET_STATE (bb, 0); } + +/* Like find_many_sub_basic_blocks, but look only within BB. */ + +void +find_sub_basic_blocks (basic_block bb) +{ + basic_block end_bb = bb->next_bb; + find_bb_boundaries (bb); + if (bb->next_bb == end_bb) + return; + + /* Re-scan and wire in all edges. This expects simple (conditional) + jumps at the end of each new basic blocks. */ + make_edges (bb, end_bb->prev_bb, 1); + + /* Update branch probabilities. Expect only (un)conditional jumps + to be created with only the forward edges. */ + if (profile_status_for_fn (cfun) != PROFILE_ABSENT) + { + compute_outgoing_frequencies (bb); + for (bb = bb->next_bb; bb != end_bb; bb = bb->next_bb) + update_profile_for_new_sub_basic_block (bb); + } +} diff --git a/gcc/cfgbuild.h b/gcc/cfgbuild.h index 51d3eccb1aec..4191fb3fcba4 100644 --- a/gcc/cfgbuild.h +++ b/gcc/cfgbuild.h @@ -24,5 +24,6 @@ extern bool inside_basic_block_p (const rtx_insn *); extern bool control_flow_insn_p (const rtx_insn *); extern void rtl_make_eh_edge (sbitmap, basic_block, rtx); extern void find_many_sub_basic_blocks (sbitmap); +extern void find_sub_basic_blocks (basic_block); #endif /* GCC_CFGBUILD_H */ diff --git a/gcc/function.cc b/gcc/function.cc index 336af28fb228..afb0b33da9e3 100644 --- a/gcc/function.cc +++ b/gcc/function.cc @@ -6112,6 +6112,8 @@ thread_prologue_and_epilogue_insns (void) && returnjump_p (BB_END (e->src))) e->flags &= ~EDGE_FALLTHRU; } + + find_sub_basic_blocks (BLOCK_FOR_INSN (epilogue_seq)); } else if (next_active_insn (BB_END (exit_fallthru_edge->src))) { @@ -6210,6 +6212,8 @@ thread_prologue_and_epilogue_insns (void) set_insn_locations (seq, epilogue_location); emit_insn_before (seq, insn); + + find_sub_basic_blocks (BLOCK_FOR_INSN (insn)); } }
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