So I was curious what would happen if I turned on LRA for m68k. It turns out my autoinc patches from the cc0 patch set expose a bug in how LRA handles autoincrement. While it copies the logic from reload's inc_for_reload, it appears to be missing the find_reloads_address code to ensure an autoinc address is reloaded entirely if it is part of a jump. LRA can reload just the register inside a POST_INC, which leads to creating an output reload.
Hence, a new version of the autoinc changes, below. Since reload is known to work, we allow autoinc in jumps unless targetm.lra_p. One part of the patch is a fix for the earlier combine patch which was already checked in, the other part is a new version of the auto-inc-dec patch. Bootstrapped and tested on the gcc135 machine (powerpc64le-unknown-linux-gnu). OK? Bernd
* auto-inc-dec.c (merge_in_block): Allow autoinc in jumps unless LRA is enabled. * combine.c (can_combine_p): Disallow autoinc in jumps unless LRA is disabled. diff --git a/gcc/auto-inc-dec.c b/gcc/auto-inc-dec.c index bdb6efab520..1b224cc9777 100644 --- a/gcc/auto-inc-dec.c +++ b/gcc/auto-inc-dec.c @@ -1441,10 +1441,9 @@ merge_in_block (int max_reg, basic_block bb) continue; } - /* This continue is deliberate. We do not want the uses of the - jump put into reg_next_use because it is not considered safe to - combine a preincrement with a jump. */ - if (JUMP_P (insn)) + /* Reload should handle auto-inc within a jump correctly, while LRA + is known to have issues with autoinc. */ + if (JUMP_P (insn) && targetm.lra_p ()) continue; if (dump_file) diff --git a/gcc/combine.c b/gcc/combine.c index 2e21459f504..3fbd84fcb80 100644 --- a/gcc/combine.c +++ b/gcc/combine.c @@ -2117,12 +2117,16 @@ can_combine_p (rtx_insn *insn, rtx_insn *i3, rtx_insn *pred ATTRIBUTE_UNUSED, /* If INSN contains an autoincrement or autodecrement, make sure that register is not used between there and I3, and not already used in - I3 either. Neither must it be used in PRED or SUCC, if they exist. */ + I3 either. Neither must it be used in PRED or SUCC, if they exist. + Also insist that I3 not be a jump if using LRA; if it were one + and the incremented register were spilled, we would lose. + Reload handles this correctly. */ if (AUTO_INC_DEC) for (link = REG_NOTES (insn); link; link = XEXP (link, 1)) if (REG_NOTE_KIND (link) == REG_INC - && (reg_used_between_p (XEXP (link, 0), insn, i3) + && ((JUMP_P (i3) && targetm.lra_p ()) + || reg_used_between_p (XEXP (link, 0), insn, i3) || (pred != NULL_RTX && reg_overlap_mentioned_p (XEXP (link, 0), PATTERN (pred))) || (pred2 != NULL_RTX