[patch] Fix problematic debug info for parameters at -O0

[Eric Botcazou]

Hi,

the fix for PR middle-end/61268:
  https://gcc.gnu.org/viewcvs/gcc?view=revision&revision=213002
changed validize_mem to modify its argument in-place, which in turns means 
that emit_move_insn can do it too.  That's a little surprising, but I guess 
not really problematic in the end, except when the RTX is shared with the 
DECL_RTL of a DECL node, because this DECL_RTL is also used for the debug info 
at -O0; it's typically a MEM based on VIRTUAL_STACK_VARS_REGNUM initially but 
it can be changed into a MEM based on a pseudo which then can be assigned a 
volatile register by RA, in which case the debug info would be based on this 
volatile register instead of the frame pointer, which can break backtraces.

The attached patch fixes one of those cases in assign_parm_setup_reg, which 
results in broken backtraces for Visium and PowerPC/EABI for some testcase.

Tested on x86_64-suse-linux, OK for the mainline?  What about the release 
branches (5 & 6 are affected), is the issue worth fixing there too?


2016-06-22  Eric Botcazou  <ebotca...@adacore.com>

        * function.c (assign_parm_setup_reg): Prevent sharing in another case.

-- 
Eric Botcazou
Index: function.c
===================================================================
--- function.c	(revision 237677)
+++ function.c	(working copy)
@@ -3314,6 +3314,8 @@ assign_parm_setup_reg (struct assign_par
 	  set_mem_attributes (parmreg, parm, 1);
 	}
 
+      /* We need to preserve an address based on VIRTUAL_STACK_VARS_REGNUM for
+	 the debug info in case it is not legitimate.  */
       if (GET_MODE (parmreg) != GET_MODE (rtl))
 	{
 	  rtx tempreg = gen_reg_rtx (GET_MODE (rtl));
@@ -3323,7 +3325,8 @@ assign_parm_setup_reg (struct assign_par
 			     all->last_conversion_insn);
 	  emit_move_insn (tempreg, rtl);
 	  tempreg = convert_to_mode (GET_MODE (parmreg), tempreg, unsigned_p);
-	  emit_move_insn (parmreg, tempreg);
+	  emit_move_insn (MEM_P (parmreg) ? copy_rtx (parmreg) : parmreg,
+			  tempreg);
 	  all->first_conversion_insn = get_insns ();
 	  all->last_conversion_insn = get_last_insn ();
 	  end_sequence ();
@@ -3331,7 +3334,7 @@ assign_parm_setup_reg (struct assign_par
 	  did_conversion = true;
 	}
       else
-	emit_move_insn (parmreg, rtl);
+	emit_move_insn (MEM_P (parmreg) ? copy_rtx (parmreg) : parmreg, rtl);
 
       rtl = parmreg;