diff options
Diffstat (limited to 'contrib/gcc/combine.c')
| -rw-r--r-- | contrib/gcc/combine.c | 51 |
1 files changed, 49 insertions, 2 deletions
diff --git a/contrib/gcc/combine.c b/contrib/gcc/combine.c index 57b2e8619bc6..0b64a86a548c 100644 --- a/contrib/gcc/combine.c +++ b/contrib/gcc/combine.c @@ -10834,9 +10834,56 @@ get_last_value (x) return 0; /* If the value was set in a later insn than the ones we are processing, - we can't use it even if the register was only set once. */ + we can't use it even if the register was only set once, but make a quick + check to see if the previous insn set it to something. This is commonly + the case when the same pseudo is used by repeated insns. + + This does not work if there exists an instruction which is temporarily + not on the insn chain. */ + if (INSN_CUID (reg_last_set[regno]) >= subst_low_cuid) - return 0; + { + rtx insn, set; + + /* We can not do anything useful in this case, because there is + an instruction which is not on the insn chain. */ + if (subst_prev_insn) + return 0; + + /* Skip over USE insns. They are not useful here, and they may have + been made by combine, in which case they do not have a INSN_CUID + value. We can't use prev_real_insn, because that would incorrectly + take us backwards across labels. Skip over BARRIERs also, since + they could have been made by combine. If we see one, we must be + optimizing dead code, so it doesn't matter what we do. */ + for (insn = prev_nonnote_insn (subst_insn); + insn && ((GET_CODE (insn) == INSN + && GET_CODE (PATTERN (insn)) == USE) + || GET_CODE (insn) == BARRIER + || INSN_CUID (insn) >= subst_low_cuid); + insn = prev_nonnote_insn (insn)) + ; + + if (insn + && (set = single_set (insn)) != 0 + && rtx_equal_p (SET_DEST (set), x)) + { + value = SET_SRC (set); + + /* Make sure that VALUE doesn't reference X. Replace any + explicit references with a CLOBBER. If there are any remaining + references (rare), don't use the value. */ + + if (reg_mentioned_p (x, value)) + value = replace_rtx (copy_rtx (value), x, + gen_rtx_CLOBBER (GET_MODE (x), const0_rtx)); + + if (reg_overlap_mentioned_p (x, value)) + return 0; + } + else + return 0; + } /* If the value has all its registers valid, return it. */ if (get_last_value_validate (&value, reg_last_set[regno], |