Autoinc vs reload and LRA

[Bernd Schmidt <bernds_cb1 at t-online dot de>]

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