diff options
Diffstat (limited to 'gcc/dce.c')
| -rw-r--r-- | gcc/dce.c | 152 |
1 files changed, 1 insertions, 151 deletions
@@ -214,62 +214,6 @@ mark_nonreg_stores (rtx body, rtx insn, bool fast) } -/* Return true if the entire libcall sequence starting at INSN is dead. - NOTE is the REG_LIBCALL note attached to INSN. - - A libcall sequence is a block of insns with no side-effects, i.e. - that is only used for its return value. The terminology derives - from that of a call, but a libcall sequence need not contain one. - It is only defined by a pair of REG_LIBCALL/REG_RETVAL notes. - - From a dataflow viewpoint, a libcall sequence has the property that - no UD chain can enter it from the outside. As a consequence, if a - libcall sequence has a dead return value, it is effectively dead. - This is both enforced by CSE (cse_extended_basic_block) and relied - upon by delete_trivially_dead_insns. - - However, in practice, the return value business is a tricky one and - only checking the liveness of the last insn is not sufficient to - decide whether the whole sequence is dead (e.g. PR middle-end/19551) - so we check the liveness of every insn starting from the call. */ - -static bool -libcall_dead_p (rtx insn, rtx note) -{ - rtx last = XEXP (note, 0); - - /* Find the call insn. */ - while (insn != last && !CALL_P (insn)) - insn = NEXT_INSN (insn); - - /* If there is none, do nothing special, since ordinary death handling - can understand these insns. */ - if (!CALL_P (insn)) - return false; - - /* If this is a call that returns a value via an invisible pointer, the - dataflow engine cannot see it so it has been marked unconditionally. - Skip it unless it has been made the last insn in the libcall, for - example by the combiner, in which case we're left with no easy way - of asserting its liveness. */ - if (!single_set (insn)) - { - if (insn == last) - return false; - insn = NEXT_INSN (insn); - } - - while (insn != NEXT_INSN (last)) - { - if (INSN_P (insn) && marked_insn_p (insn)) - return false; - insn = NEXT_INSN (insn); - } - - return true; -} - - /* Delete all REG_EQUAL notes of the registers INSN writes, to prevent bad dangling REG_EQUAL notes. */ @@ -316,29 +260,10 @@ delete_unmarked_insns (void) FOR_BB_INSNS_SAFE (bb, insn, next) if (INSN_P (insn)) { - rtx note = find_reg_note (insn, REG_LIBCALL, NULL_RTX); - /* Always delete no-op moves. */ if (noop_move_p (insn)) ; - /* Try to delete libcall sequences as a whole. */ - else if (note && libcall_dead_p (insn, note)) - { - rtx last = XEXP (note, 0); - - if (!dbg_cnt (dce)) - continue; - - if (dump_file) - fprintf (dump_file, "DCE: Deleting libcall %d-%d\n", - INSN_UID (insn), INSN_UID (last)); - - next = NEXT_INSN (last); - delete_insn_chain_and_edges (insn, last); - continue; - } - /* Otherwise rely only on the DCE algorithm. */ else if (marked_insn_p (insn)) continue; @@ -353,41 +278,6 @@ delete_unmarked_insns (void) for the destination regs in order to avoid dangling notes. */ delete_corresponding_reg_eq_notes (insn); - /* If we're about to delete the first insn of a libcall, then - move the REG_LIBCALL note to the next real insn and update - the REG_RETVAL note. */ - if (note && (XEXP (note, 0) != insn)) - { - rtx new_libcall_insn = next_real_insn (insn); - rtx retval_note = find_reg_note (XEXP (note, 0), - REG_RETVAL, NULL_RTX); - /* If the RETVAL and LIBCALL notes would land on the same - insn just remove them. */ - if (XEXP (note, 0) == new_libcall_insn) - remove_note (new_libcall_insn, retval_note); - else - { - REG_NOTES (new_libcall_insn) - = gen_rtx_INSN_LIST (REG_LIBCALL, XEXP (note, 0), - REG_NOTES (new_libcall_insn)); - XEXP (retval_note, 0) = new_libcall_insn; - } - } - - /* If the insn contains a REG_RETVAL note and is dead, but the - libcall as a whole is not dead, then we want to remove the - insn, but not the whole libcall sequence. However, we also - need to remove the dangling REG_LIBCALL note in order to - avoid mismatched notes. We could find a new location for - the REG_RETVAL note, but it hardly seems worth the effort. */ - note = find_reg_note (insn, REG_RETVAL, NULL_RTX); - if (note && (XEXP (note, 0) != insn)) - { - rtx libcall_note - = find_reg_note (XEXP (note, 0), REG_LIBCALL, NULL_RTX); - remove_note (XEXP (note, 0), libcall_note); - } - /* If a pure or const call is deleted, this may make the cfg have unreachable blocks. We rememeber this and call delete_unreachable_blocks at the end. */ @@ -404,43 +294,6 @@ delete_unmarked_insns (void) } -/* Helper function for prescan_insns_for_dce: prescan the entire libcall - sequence starting at INSN and return the insn following the libcall. - NOTE is the REG_LIBCALL note attached to INSN. */ - -static rtx -prescan_libcall_for_dce (rtx insn, rtx note, bool fast) -{ - rtx last = XEXP (note, 0); - - /* A libcall is never necessary on its own but we need to mark the stores - to a non-register destination. */ - while (insn != last && !CALL_P (insn)) - { - if (INSN_P (insn)) - mark_nonreg_stores (PATTERN (insn), insn, fast); - insn = NEXT_INSN (insn); - } - - /* If this is a call that returns a value via an invisible pointer, the - dataflow engine cannot see it so it has to be marked unconditionally. */ - if (CALL_P (insn) && !single_set (insn)) - { - mark_insn (insn, fast); - insn = NEXT_INSN (insn); - } - - while (insn != NEXT_INSN (last)) - { - if (INSN_P (insn)) - mark_nonreg_stores (PATTERN (insn), insn, fast); - insn = NEXT_INSN (insn); - } - - return insn; -} - - /* Go through the instructions and mark those whose necessity is not dependent on inter-instruction information. Make sure all other instructions are not marked. */ @@ -458,10 +311,7 @@ prescan_insns_for_dce (bool fast) FOR_BB_INSNS_SAFE (bb, insn, next) if (INSN_P (insn)) { - rtx note = find_reg_note (insn, REG_LIBCALL, NULL_RTX); - if (note) - next = prescan_libcall_for_dce (insn, note, fast); - else if (deletable_insn_p (insn, fast)) + if (deletable_insn_p (insn, fast)) mark_nonreg_stores (PATTERN (insn), insn, fast); else mark_insn (insn, fast); |