2013-02-08  Jeff Law  <law@redhat.com>

	PR debug/53948
	* emit-rtl.c (reg_is_parm_p): New function.
	* regs.h (reg_is_parm_p): New prototype.
	* ira-conflicts.c (ira_build_conflicts): Allow parameters in
	callee-clobbered registers.

	* gcc.dg/debug/dwarf2/pr53948.c: New test.

--- gcc/emit-rtl.c
+++ gcc/emit-rtl.c
@@ -919,6 +919,18 @@ gen_reg_rtx (enum machine_mode mode)
   return val;
 }
 
+/* Return TRUE if REG is a PARM_DECL, FALSE otherwise.  */
+
+bool
+reg_is_parm_p (rtx reg)
+{
+  tree decl;
+
+  gcc_assert (REG_P (reg));
+  decl = REG_EXPR (reg);
+  return (decl && TREE_CODE (decl) == PARM_DECL);
+}
+
 /* Update NEW with the same attributes as REG, but with OFFSET added
    to the REG_OFFSET.  */
 
--- gcc/ira-conflicts.c
+++ gcc/ira-conflicts.c
@@ -895,8 +895,12 @@ ira_build_conflicts (void)
 
 	  if ((! flag_caller_saves && ALLOCNO_CALLS_CROSSED_NUM (a) != 0)
 	      /* For debugging purposes don't put user defined variables in
-		 callee-clobbered registers.  */
-	      || (optimize == 0 && REG_USERVAR_P (allocno_reg)))
+		 callee-clobbered registers.  However, do allow parameters
+		 in callee-clobbered registers to improve debugging.  This
+		 is a bit of a fragile hack.  */
+	      || (optimize == 0
+		  && REG_USERVAR_P (allocno_reg)
+		  && ! reg_is_parm_p (allocno_reg)))
 	    {
 	      IOR_HARD_REG_SET (OBJECT_TOTAL_CONFLICT_HARD_REGS (obj),
 				call_used_reg_set);
--- gcc/regs.h
+++ gcc/regs.h
@@ -89,6 +89,8 @@ REG_N_SETS (int regno)
 #define SET_REG_N_SETS(N,V) (regstat_n_sets_and_refs[N].sets = V)
 #define INC_REG_N_SETS(N,V) (regstat_n_sets_and_refs[N].sets += V)
 
+/* Given a REG, return TRUE if the reg is a PARM_DECL, FALSE otherwise.  */
+extern bool reg_is_parm_p (rtx);
 
 /* Functions defined in regstat.c.  */
 extern void regstat_init_n_sets_and_refs (void);
--- gcc/testsuite/gcc.dg/debug/dwarf2/pr53948.c	2012-11-17 15:43:17.572007394 +0100
+++ gcc/testsuite/gcc.dg/debug/dwarf2/pr53948.c	2013-02-08 19:10:23.000000000 +0100
@@ -0,0 +1,10 @@
+/* Test that we emit a .line directive for the line
+   with local variable initializations.  */
+/* { dg-options "-O0 -g -dA" } */
+/* { dg-final { scan-assembler ".loc 1 8 0|# line 8" } } */
+
+
+int f (register int a, register int b) {
+  register int x = b, y = a;
+  return x + y; }
+