combine.c (get_last_value): If the last set of a register is after subst_low_cuid...

        * combine.c (get_last_value): If the last set of a register
        is after subst_low_cuid, then we can not use it to determine
        the register's last value.

From-SVN: r30062

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 86a27438bafd62ab54617ca092d2387b2e985b07..4bbe8e9b077d9104279f1604a6aadebc4c4d7900 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+Mon Oct 18 01:41:35 1999  Jeffrey A Law  (law@cygnus.com)
+
+       * combine.c (get_last_value): If the last set of a register
+       is after subst_low_cuid, then we can not use it to determine
+       the register's last value.
+
 Sun Oct 17 11:02:52 1999  Mark Mitchell  <mark@codesourcery.com>
 
        * Makefile.in: Back out previous change.

diff --git a/gcc/combine.c b/gcc/combine.c
index 7273e8f237e207b23ee62fe0f2337fc0630ce2e1..4ed1124a3dcb5c318e297c7a268f027f8ca0717e 100644 (file)
--- a/gcc/combine.c
+++ b/gcc/combine.c
@@ -10952,61 +10952,9 @@ 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, 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.  */
-
+     we can't use it even if the register was only set once.  */
   if (INSN_CUID (reg_last_set[regno]) >= subst_low_cuid)
-    {
-      rtx insn, set;
-
-      /* We can't do anything if the value is set in between the insns we are
-        processing.  */
-      if (INSN_CUID (reg_last_set[regno]) <= INSN_CUID (subst_insn))
-       return 0;
-
-      /* 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;
-    }
+    return 0;
 
   /* If the value has all its registers valid, return it.  */
   if (get_last_value_validate (&value, reg_last_set[regno],