diff options
Diffstat (limited to 'gcc/stmt.c')
| -rw-r--r-- | gcc/stmt.c | 142 |
1 files changed, 124 insertions, 18 deletions
diff --git a/gcc/stmt.c b/gcc/stmt.c index 43cf7f82ec2..18ca944ee2d 100644 --- a/gcc/stmt.c +++ b/gcc/stmt.c @@ -1923,17 +1923,33 @@ expand_end_loop () do_pending_stack_adjust (); - /* If optimizing, perhaps reorder the loop. If the loop - starts with a conditional exit, roll that to the end - where it will optimize together with the jump back. - - We look for the last conditional branch to the exit that we encounter - before hitting 30 insns or a CALL_INSN. If we see an unconditional - branch to the exit first, use it. - - We must also stop at NOTE_INSN_BLOCK_BEG and NOTE_INSN_BLOCK_END notes - because moving them is not valid. */ - + /* If optimizing, perhaps reorder the loop. If the loop starts with + a loop exit, roll that to the end where it will optimize together + with the jump back. + + We look for the conditional branch to the exit, except that once + we find such a branch, we don't look past 30 instructions. + + In more detail, if the loop presently looks like this (in pseudo-C): + + start_label: + if (test) goto end_label; + body; + goto start_label; + end_label; + + transform it to look like: + + goto start_label; + newstart_label: + body; + start_label: + if (test) goto end_label; + goto newstart_label; + end_label; + + Here, the `test' may actually consist of some reasonably complex + code, terminating in a test. */ if (optimize && ! (GET_CODE (insn) == JUMP_INSN @@ -1941,18 +1957,46 @@ expand_end_loop () && SET_DEST (PATTERN (insn)) == pc_rtx && GET_CODE (SET_SRC (PATTERN (insn))) == IF_THEN_ELSE)) { + int eh_regions = 0; + /* Scan insns from the top of the loop looking for a qualified conditional exit. */ for (insn = NEXT_INSN (loop_stack->data.loop.start_label); insn; insn = NEXT_INSN (insn)) { - if (GET_CODE (insn) == CALL_INSN || GET_CODE (insn) == CODE_LABEL) - break; + if (GET_CODE (insn) == NOTE) + { + if (optimize < 2 + && (NOTE_LINE_NUMBER (insn) == NOTE_INSN_BLOCK_BEG + || NOTE_LINE_NUMBER (insn) == NOTE_INSN_BLOCK_END)) + /* The code that actually moves the exit test will + carefully leave BLOCK notes in their original + location. That means, however, that we can't debug + the exit test itself. So, we refuse to move code + containing BLOCK notes at low optimization levels. */ + break; + + if (NOTE_LINE_NUMBER (insn) == NOTE_INSN_EH_REGION_BEG) + ++eh_regions; + else if (NOTE_LINE_NUMBER (insn) == NOTE_INSN_EH_REGION_END) + { + --eh_regions; + if (eh_regions < 0) + /* We've come to the end of an EH region, but + never saw the beginning of that region. That + means that an EH region begins before the top + of the loop, and ends in the middle of it. The + existence of such a situation violates a basic + assumption in this code, since that would imply + that even when EH_REGIONS is zero, we might + move code out of an exception region. */ + abort (); + } - if (GET_CODE (insn) == NOTE - && (NOTE_LINE_NUMBER (insn) == NOTE_INSN_BLOCK_BEG - || NOTE_LINE_NUMBER (insn) == NOTE_INSN_BLOCK_END)) - break; + /* We already know this INSN is a NOTE, so there's no + point in looking at it to see if it's a JUMP. */ + continue; + } if (GET_CODE (insn) == JUMP_INSN || GET_CODE (insn) == INSN) num_insns++; @@ -1960,6 +2004,36 @@ expand_end_loop () if (last_test_insn && num_insns > 30) break; + if (eh_regions > 0) + /* We don't want to move a partial EH region. Consider: + + while ( ( { try { + if (cond ()) 0; + else { + bar(); + 1; + } + } catch (...) { + 1; + } )) { + body; + } + + This isn't legal C++, but here's what it's supposed to + mean: if cond() is true, stop looping. Otherwise, + call bar, and keep looping. In addition, if cond + throws an exception, catch it and keep looping. Such + constructs are certainy legal in LISP. + + We should not move the `if (cond()) 0' test since then + the EH-region for the try-block would be broken up. + (In this case we would the EH_BEG note for the `try' + and `if cond()' but not the call to bar() or the + EH_END note.) + + So we don't look for tests within an EH region. */ + continue; + if (GET_CODE (insn) == JUMP_INSN && GET_CODE (PATTERN (insn)) == SET && SET_DEST (PATTERN (insn)) == pc_rtx && GET_CODE (SET_SRC (PATTERN (insn))) == IF_THEN_ELSE @@ -1994,6 +2068,7 @@ expand_end_loop () to jump to there. */ register rtx newstart_label = gen_label_rtx (); register rtx start_move = start_label; + rtx next_insn; /* If the start label is preceded by a NOTE_INSN_LOOP_CONT note, then we want to move this note also. */ @@ -2003,7 +2078,38 @@ expand_end_loop () start_move = PREV_INSN (start_move); emit_label_after (newstart_label, PREV_INSN (start_move)); - reorder_insns (start_move, last_test_insn, get_last_insn ()); + + /* Actually move the insns. Start at the beginning, and + keep copying insns until we've copied the + last_test_insn. */ + for (insn = start_move; insn; insn = next_insn) + { + /* Figure out which insn comes after this one. We have + to do this before we move INSN. */ + if (insn == last_test_insn) + /* We've moved all the insns. */ + next_insn = NULL_RTX; + else + next_insn = NEXT_INSN (insn); + + if (GET_CODE (insn) == NOTE + && (NOTE_LINE_NUMBER (insn) == NOTE_INSN_BLOCK_BEG + || NOTE_LINE_NUMBER (insn) == NOTE_INSN_BLOCK_END)) + /* We don't want to move NOTE_INSN_BLOCK_BEGs or + NOTE_INSN_BLOCK_ENDs because the correct generation + of debugging information depends on these appearing + in the same order in the RTL and in the tree + structure, where they are represented as BLOCKs. + So, we don't move block notes. Of course, moving + the code inside the block is likely to make it + impossible to debug the instructions in the exit + test, but such is the price of optimization. */ + continue; + + /* Move the INSN. */ + reorder_insns (insn, insn, get_last_insn ()); + } + emit_jump_insn_after (gen_jump (start_label), PREV_INSN (newstart_label)); emit_barrier_after (PREV_INSN (newstart_label)); |