[Xtensa] Catch more unaligned loops

[Sterling Augustine <sterling at tensilica dot com>]

I have committed the attached patch which catches more unaligned loop 
instructions than the previous code. In particular, in ensures that the 
second loop in the the illogical, but legal, "loop aX, foo\nloop aY, 
bar" construct is aligned.

Sterling

2010-02-10  Sterling Augustine  <sterling@tensilica.com>

	* config/tc-xtensa.c (xtensa_find_unaligned_loops): Rewrite.

Index: config/tc-xtensa.c
===================================================================
RCS file: /cvs/src/src/gas/config/tc-xtensa.c,v
retrieving revision 1.120
diff -u -p -r1.120 tc-xtensa.c
--- config/tc-xtensa.c	8 Feb 2010 18:45:05 -0000	1.120
+++ config/tc-xtensa.c	9 Feb 2010 19:26:22 -0000
@@ -4649,6 +4649,12 @@ next_frag_is_loop_target (const fragS *f
 }
 
 
+/* As specified in the relaxation table, when a loop instruction is
+   relaxed, there are 24 bytes between the loop instruction itself and
+   the first instruction in the loop.  */
+
+#define RELAXED_LOOP_INSN_BYTES 24
+
 static addressT
 next_frag_pre_opcode_bytes (const fragS *fragp)
 {
@@ -4671,7 +4677,7 @@ next_frag_pre_opcode_bytes (const fragS 
      been relaxed.  Note that we can assume that the LOOP
      instruction is in slot 0 because loops aren't bundleable.  */
   if (next_fragp->tc_frag_data.slot_subtypes[0] > RELAX_IMMED)
-      return get_expanded_loop_offset (next_opcode);
+      return get_expanded_loop_offset (next_opcode) + RELAXED_LOOP_INSN_BYTES;
 
   return 0;
 }
@@ -7401,9 +7407,36 @@ xtensa_mark_zcl_first_insns (void)
 		    || fragP->fr_subtype == RELAX_CHECK_ALIGN_NEXT_OPCODE))
 	      {
 		/* Find the loop frag.  */
-		fragS *targ_frag = next_non_empty_frag (fragP);
+		fragS *loop_frag = next_non_empty_frag (fragP);
 		/* Find the first insn frag.  */
-		targ_frag = next_non_empty_frag (targ_frag);
+		fragS *targ_frag = next_non_empty_frag (loop_frag);
+
+	      /* Handle a corner case that comes up in hardware
+		 diagnostics.  The original assembly looks like this:
+		 
+		 loop aX, LabelA
+		 <empty_frag>--not found by next_non_empty_frag
+		 loop aY, LabelB
+
+		 Depending on the start address, the assembler may or
+		 may not change it to look something like this:
+
+		 loop aX, LabelA
+		 nop--frag isn't empty anymore
+		 loop aY, LabelB
+
+		 So set up to check the alignment of the nop if it
+		 exists  */
+		while (loop_frag != targ_frag)
+		  {
+		    if (loop_frag->fr_type == rs_machine_dependent
+			&& (loop_frag->fr_subtype == RELAX_ALIGN_NEXT_OPCODE
+			    || loop_frag->fr_subtype 
+			    == RELAX_CHECK_ALIGN_NEXT_OPCODE))
+		      targ_frag = loop_frag;
+		    else
+		      loop_frag = loop_frag->fr_next;
+		  }
 
 		/* Of course, sometimes (mostly for toy test cases) a
 		   zero-cost loop instruction is the last in a section.  */