[3/3 patch, nios2] clean up prologue/epilogue detection code, v2

[Sandra Loosemore <sandra@codesourcery.com>]

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This part of the revised Nios II prologue/epilogue refactoring patch 
fixes the prologue analyzer to handle the multiple stack adjustment 
instructions that GCC may now emit in some cases.  It replaces the test 
that caused analysis to terminate when a second adjustment is found with 
more specific tests that can distinguish between prologue-ish and 
epilogue-ish adjustments.

OK to commit on top of part 1?

-Sandra

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2014-11-24  Sandra Loosemore  <sandra@codesourcery.com>

	gdb/
	* nios2-tdep.c (nios2_analyze_prologue): Replace restriction
	that there can be only one stack adjustment in the prologue
	with tests to detect specific disallowed stack adjustments.

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diff -u b/gdb/nios2-tdep.c b/gdb/nios2-tdep.c
--- b/gdb/nios2-tdep.c
+++ b/gdb/nios2-tdep.c
@@ -842,6 +842,11 @@
 	      cache->reg_saved[NIOS2_SP_REGNUM].addr = -4;
 	    }
 
+	  else if (rc == NIOS2_SP_REGNUM && ra == NIOS2_FP_REGNUM)
+	    /* This is setting SP from FP.  This only happens in the
+	       function epilogue.  */
+	    break;
+
 	  else if (rc != 0)
 	    {
 	      if (value[rb].reg == 0)
@@ -853,13 +858,21 @@
 	      value[rc].offset = value[ra].offset + value[rb].offset;
 	    }
 
-	  prologue_end = pc;
+	  /* The add/move is only considered a prologue instruction
+	     if the destination is SP or FP.  */
+	  if (rc == NIOS2_SP_REGNUM || rc == NIOS2_FP_REGNUM)
+	    prologue_end = pc;
 	}
       
       else if (nios2_match_sub (insn, op, mach, &ra, &rb, &rc))
 	{
 	  /* SUB   rc, ra, rb */
-	  if (rc != 0)
+	  if (rc == NIOS2_SP_REGNUM && rb == NIOS2_SP_REGNUM
+	      && value[rc].reg != 0)
+	    /* If we are decrementing the SP by a non-constant amount,
+	       this is alloca, not part of the prologue.  */
+	    break;
+	  else if (rc != 0)
 	    {
 	      if (value[rb].reg == 0)
 		value[rc].reg = value[ra].reg;
@@ -873,12 +886,13 @@
 	{
 	  /* ADDI    rb, ra, imm */
 
-	  /* The first stack adjustment is part of the prologue.
-	     Any subsequent stack adjustments are either down to
-	     alloca or the epilogue so stop analysing when we hit
-	     them.  */
+	  /* A positive stack adjustment has to be part of the epilogue.  */
 	  if (rb == NIOS2_SP_REGNUM
-	      && (value[rb].offset != 0 || value[ra].reg != NIOS2_SP_REGNUM))
+	      && (imm > 0 || value[ra].reg != NIOS2_SP_REGNUM))
+	    break;
+
+	  /* Likewise restoring SP from FP.  */
+	  else if (rb == NIOS2_SP_REGNUM && ra == NIOS2_FP_REGNUM)
 	    break;
 
 	  if (rb != 0)
@@ -887,7 +901,10 @@
 	      value[rb].offset = value[ra].offset + imm;
 	    }
 
-	  prologue_end = pc;
+	  /* The add is only considered a prologue instruction
+	     if the destination is SP or FP.  */
+	  if (rb == NIOS2_SP_REGNUM || rb == NIOS2_FP_REGNUM)
+	    prologue_end = pc;
 	}
 
       else if (nios2_match_orhi (insn, op, mach, &ra, &rb, &uimm))