[PATCH] For mem_loc_descriptor prefer avoid_constant_pool_reference (PR debug/50191)

[Jakub Jelinek]

Hi!

On PowerPC64 PR50191 testcase when linked together with other code
results in linker crash.  The problem is that a reference
to a constant pool stays in the .debug_loc section.  During var-tracking
adjust_insn doesn't successfully avoid_constant_pool_reference it
because instead of a REG it uses a DEBUG_EXPR (as the register is no
longer live at that point), and rs6000_delegitimize_address checks
only for REGs in that part of the TOCREL expression.  And in dwarf2out.c
we were prefering DW_OP_deref* over avoid_constant_pool_reference,
performed the latter only if mem_loc_descriptor on the address failed.

The following patch changes it to prefer avoid_constant_pool_reference.
I think we can do this in mem_loc_descriptor, because MEMs handled
by that routine are otherwise DW_OP_deref*, i.e. DWARF expression rvalues
anyway.  I'm not changing loc_descriptor, because there we want to
prefer getting a REG or MEM which can be changed.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

2011-09-05  Jakub Jelinek  <jakub@redhat.com>

	PR debug/50191
	* dwarf2out.c (mem_loc_descriptor) <case MEM>: Try
	avoid_constant_pool_reference first instead of last.

--- gcc/dwarf2out.c.jj	2011-07-29 17:07:20.000000000 +0200
+++ gcc/dwarf2out.c	2011-09-05 09:59:41.000000000 +0200
@@ -11695,12 +11695,22 @@ mem_loc_descriptor (rtx rtl, enum machin
       break;
 
     case MEM:
+      {
+	rtx new_rtl = avoid_constant_pool_reference (rtl);
+	if (new_rtl != rtl)
+	  {
+	    mem_loc_result = mem_loc_descriptor (new_rtl, mode, mem_mode,
+						 initialized);
+	    if (mem_loc_result != NULL)
+	      return mem_loc_result;
+	  }
+      }
       mem_loc_result = mem_loc_descriptor (XEXP (rtl, 0),
 					   get_address_mode (rtl), mode,
 					   VAR_INIT_STATUS_INITIALIZED);
       if (mem_loc_result == NULL)
 	mem_loc_result = tls_mem_loc_descriptor (rtl);
-      if (mem_loc_result != 0)
+      if (mem_loc_result != NULL)
 	{
 	  if (GET_MODE_SIZE (mode) > DWARF2_ADDR_SIZE
 	      || GET_MODE_CLASS (mode) != MODE_INT)
@@ -11728,12 +11738,6 @@ mem_loc_descriptor (rtx rtl, enum machin
 			   new_loc_descr (DW_OP_deref_size,
 					  GET_MODE_SIZE (mode), 0));
 	}
-      else
-	{
-	  rtx new_rtl = avoid_constant_pool_reference (rtl);
-	  if (new_rtl != rtl)
-	    return mem_loc_descriptor (new_rtl, mode, mem_mode, initialized);
-	}
       break;
 
     case LO_SUM:

	Jakub