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[PATCH] Optimize DW_OP_{breg{[0-9],[12][0-9],3[01],x},fbreg} followed by DW_OP_plus_uconst


Hi!

When working on the patch I've just posted, I've noticed a lot of
sequences like:
        .byte   0x73    # DW_OP_breg3
        .sleb128 0
        .byte   0x23    # DW_OP_plus_uconst
        .uleb128 0x98
        .byte   0x6     # DW_OP_deref
or
        .byte   0x91    # DW_OP_fbreg
        .sleb128 -1872
        .byte   0x23    # DW_OP_plus_uconst
        .uleb128 0x70
in .debug_info.  We can merge the constant addition with the breg*/fbreg
offset in most cases.  This patch creates a new function for that and
uses it in all places that were deciding if DW_OP_plus_uconst or DW_OP_plus
should be used.

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

2009-04-08  Jakub Jelinek  <jakub@redhat.com>

	* dwarf2out.c (loc_descr_plus_const): New function.
	(build_cfa_aligned_loc, tls_mem_loc_descriptor,
	mem_loc_descriptor, loc_descriptor_from_tree_1,
	descr_info_loc, gen_variable_die): Use it.

--- gcc/dwarf2out.c.jj	2009-04-08 11:10:16.000000000 +0200
+++ gcc/dwarf2out.c	2009-04-08 12:52:16.000000000 +0200
@@ -3890,6 +3890,47 @@ add_loc_descr (dw_loc_descr_ref *list_he
   *d = descr;
 }
 
+/* Add a constant OFFSET to a location expression.  */
+
+static void
+loc_descr_plus_const (dw_loc_descr_ref *list_head, HOST_WIDE_INT offset)
+{
+  dw_loc_descr_ref loc;
+  HOST_WIDE_INT *p;
+
+  gcc_assert (*list_head != NULL);
+
+  if (!offset)
+    return;
+
+  /* Find the end of the chain.  */
+  for (loc = *list_head; loc->dw_loc_next != NULL; loc = loc->dw_loc_next)
+    ;
+
+  p = NULL;
+  if (loc->dw_loc_opc == DW_OP_fbreg
+      || (loc->dw_loc_opc >= DW_OP_breg0 && loc->dw_loc_opc <= DW_OP_breg31))
+    p = &loc->dw_loc_oprnd1.v.val_int;
+  else if (loc->dw_loc_opc == DW_OP_bregx)
+    p = &loc->dw_loc_oprnd2.v.val_int;
+
+  /* If the last operation is fbreg, breg{0..31,x}, optimize by adjusting its
+     offset.  Don't optimize if an signed integer overflow would happen.  */
+  if (p != NULL
+      && ((offset > 0 && *p <= INTTYPE_MAXIMUM (HOST_WIDE_INT) - offset)
+	  || (offset < 0 && *p >= INTTYPE_MINIMUM (HOST_WIDE_INT) - offset)))
+    *p += offset;
+
+  else if (offset > 0)
+    loc->dw_loc_next = new_loc_descr (DW_OP_plus_uconst, offset, 0);
+
+  else
+    {
+      loc->dw_loc_next = int_loc_descriptor (offset);
+      add_loc_descr (&loc->dw_loc_next, new_loc_descr (DW_OP_plus, 0, 0));
+    }
+}
+
 /* Return the size of a location descriptor.  */
 
 static unsigned long
@@ -4409,9 +4450,7 @@ build_cfa_aligned_loc (HOST_WIDE_INT off
       head = new_reg_loc_descr (dwarf_fp, 0);
       add_loc_descr (&head, int_loc_descriptor (alignment));
       add_loc_descr (&head, new_loc_descr (DW_OP_and, 0, 0));
-
-      add_loc_descr (&head, int_loc_descriptor (offset));
-      add_loc_descr (&head, new_loc_descr (DW_OP_plus, 0, 0));
+      loc_descr_plus_const (&head, offset);
     }
   else
     head = new_reg_loc_descr (dwarf_fp, offset);
@@ -9913,7 +9952,7 @@ static dw_loc_descr_ref
 tls_mem_loc_descriptor (rtx mem)
 {
   tree base;
-  dw_loc_descr_ref loc_result, loc_result2;
+  dw_loc_descr_ref loc_result;
 
   if (MEM_EXPR (mem) == NULL_TREE || MEM_OFFSET (mem) == NULL_RTX)
     return NULL;
@@ -9929,21 +9968,7 @@ tls_mem_loc_descriptor (rtx mem)
     return NULL;
 
   if (INTVAL (MEM_OFFSET (mem)))
-    {
-      if (INTVAL (MEM_OFFSET (mem)) >= 0)
-	add_loc_descr (&loc_result,
-		       new_loc_descr (DW_OP_plus_uconst,
-				      INTVAL (MEM_OFFSET (mem)), 0));
-      else
-	{
-	  loc_result2 = mem_loc_descriptor (MEM_OFFSET (mem), GET_MODE (mem),
-					    VAR_INIT_STATUS_INITIALIZED);
-	  if (loc_result2 == 0)
-	    return NULL;
-	  add_loc_descr (&loc_result, loc_result2);
-	  add_loc_descr (&loc_result, new_loc_descr (DW_OP_plus, 0, 0));
-	}
-    }
+    loc_descr_plus_const (&loc_result, INTVAL (MEM_OFFSET (mem)));
 
   return loc_result;
 }
@@ -10108,11 +10133,8 @@ mem_loc_descriptor (rtx rtl, enum machin
 	  if (mem_loc_result == 0)
 	    break;
 
-	  if (GET_CODE (XEXP (rtl, 1)) == CONST_INT
-	      && INTVAL (XEXP (rtl, 1)) >= 0)
-	    add_loc_descr (&mem_loc_result,
-			   new_loc_descr (DW_OP_plus_uconst,
-					  INTVAL (XEXP (rtl, 1)), 0));
+	  if (GET_CODE (XEXP (rtl, 1)) == CONST_INT)
+	    loc_descr_plus_const (&mem_loc_result, INTVAL (XEXP (rtl, 1)));
 	  else
 	    {
 	      dw_loc_descr_ref mem_loc_result2
@@ -10526,13 +10548,7 @@ loc_descriptor_from_tree_1 (tree loc, in
 	  }
 
 	bytepos = bitpos / BITS_PER_UNIT;
-	if (bytepos > 0)
-	  add_loc_descr (&ret, new_loc_descr (DW_OP_plus_uconst, bytepos, 0));
-	else if (bytepos < 0)
-	  {
-	    add_loc_descr (&ret, int_loc_descriptor (bytepos));
-	    add_loc_descr (&ret, new_loc_descr (DW_OP_plus, 0, 0));
-	  }
+	loc_descr_plus_const (&ret, bytepos);
 
 	have_address = 1;
 	break;
@@ -10616,11 +10632,7 @@ loc_descriptor_from_tree_1 (tree loc, in
 	  if (ret == 0)
 	    return 0;
 
-	  add_loc_descr (&ret,
-			 new_loc_descr (DW_OP_plus_uconst,
-					tree_low_cst (TREE_OPERAND (loc, 1),
-						      0),
-					0));
+	  loc_descr_plus_const (&ret, tree_low_cst (TREE_OPERAND (loc, 1), 0));
 	  break;
 	}
 
@@ -13001,10 +13013,7 @@ descr_info_loc (tree val, tree base_decl
 	  loc = descr_info_loc (TREE_OPERAND (val, 0), base_decl);
 	  if (!loc)
 	    break;
-	  add_loc_descr (&loc,
-			 new_loc_descr (DW_OP_plus_uconst,
-					tree_low_cst (TREE_OPERAND (val, 1),
-						      1), 0));
+	  loc_descr_plus_const (&loc, tree_low_cst (TREE_OPERAND (val, 1), 0));
 	}
       else
 	{
@@ -13920,9 +13929,7 @@ gen_variable_die (tree decl, tree origin
 			loc->dw_loc_oprnd1.v.val_addr
 			  = plus_constant (loc->dw_loc_oprnd1.v.val_addr, off);
 			else
-			  add_loc_descr (&loc,
-					 new_loc_descr (DW_OP_plus_uconst,
-							off, 0));
+			  loc_descr_plus_const (&loc, off);
 		    }
 		  add_AT_loc (var_die, DW_AT_location, loc);
 		  remove_AT (var_die, DW_AT_declaration);
@@ -13985,8 +13992,7 @@ gen_variable_die (tree decl, tree origin
 		loc->dw_loc_oprnd1.v.val_addr
 		  = plus_constant (loc->dw_loc_oprnd1.v.val_addr, off);
 	      else
-		add_loc_descr (&loc, new_loc_descr (DW_OP_plus_uconst,
-						    off, 0));
+		loc_descr_plus_const (&loc, off);
 	    }
 	  add_AT_loc (var_die, DW_AT_location, loc);
 	}

	Jakub


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