diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index f887654193b..7cdd2926f6e 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,11 @@
+2005-08-31  Richard Henderson  <rth@redhat.com>
+
+	* emit-rtl.c (set_mem_attributes_minus_bitpos): Look through
+	component-like references for setting MEM_NOTRAP_P.
+
+	* config/i386/i386.c (ix86_setup_incoming_varargs): Set MEM_NOTRAP_P.
+	* config/alpha/alpha.c (alpha_setup_incoming_varargs): Likewise.
+
 2005-08-31  Richard Henderson  <rth@redhat.com>
 
 	* expr.c (expand_expr_real_1) <VIEW_CONVERT_EXPR>: Force subregs
diff --git a/gcc/config/alpha/alpha.c b/gcc/config/alpha/alpha.c
index f15964fd7f6..808116a158d 100644
--- a/gcc/config/alpha/alpha.c
+++ b/gcc/config/alpha/alpha.c
@@ -6090,6 +6090,7 @@ alpha_setup_incoming_varargs (CUMULATIVE_ARGS *pcum, enum machine_mode mode,
 	  tmp = gen_rtx_MEM (BLKmode,
 			     plus_constant (virtual_incoming_args_rtx,
 					    (cum + 6) * UNITS_PER_WORD));
+	  MEM_NOTRAP_P (tmp) = 1;
 	  set_mem_alias_set (tmp, set);
 	  move_block_from_reg (16 + cum, tmp, count);
 	}
@@ -6099,6 +6100,7 @@ alpha_setup_incoming_varargs (CUMULATIVE_ARGS *pcum, enum machine_mode mode,
 	  tmp = gen_rtx_MEM (BLKmode,
 			     plus_constant (virtual_incoming_args_rtx,
 					    cum * UNITS_PER_WORD));
+	  MEM_NOTRAP_P (tmp) = 1;
 	  set_mem_alias_set (tmp, set);
 	  move_block_from_reg (16 + cum + TARGET_FPREGS*32, tmp, count);
 	}
diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
index e3fd6e7a75d..5f12d1a5f7e 100644
--- a/gcc/config/i386/i386.c
+++ b/gcc/config/i386/i386.c
@@ -3682,6 +3682,7 @@ ix86_setup_incoming_varargs (CUMULATIVE_ARGS *cum, enum machine_mode mode,
     {
       mem = gen_rtx_MEM (Pmode,
 			 plus_constant (save_area, i * UNITS_PER_WORD));
+      MEM_NOTRAP_P (mem) = 1;
       set_mem_alias_set (mem, set);
       emit_move_insn (mem, gen_rtx_REG (Pmode,
 					x86_64_int_parameter_registers[i]));
@@ -3724,6 +3725,7 @@ ix86_setup_incoming_varargs (CUMULATIVE_ARGS *cum, enum machine_mode mode,
 			      plus_constant (save_area,
 					     8 * REGPARM_MAX + 127)));
       mem = gen_rtx_MEM (BLKmode, plus_constant (tmp_reg, -127));
+      MEM_NOTRAP_P (mem) = 1;
       set_mem_alias_set (mem, set);
       set_mem_align (mem, BITS_PER_WORD);
 
diff --git a/gcc/emit-rtl.c b/gcc/emit-rtl.c
index 18c71b14890..d9e253e3ce2 100644
--- a/gcc/emit-rtl.c
+++ b/gcc/emit-rtl.c
@@ -1469,7 +1469,6 @@ set_mem_attributes_minus_bitpos (rtx ref, tree t, int objectp,
   MEM_VOLATILE_P (ref) |= TYPE_VOLATILE (type);
   MEM_IN_STRUCT_P (ref) = AGGREGATE_TYPE_P (type);
   MEM_POINTER (ref) = POINTER_TYPE_P (type);
-  MEM_NOTRAP_P (ref) = TREE_THIS_NOTRAP (t);
 
   /* If we are making an object of this type, or if this is a DECL, we know
      that it is a scalar if the type is not an aggregate.  */
@@ -1500,16 +1499,7 @@ set_mem_attributes_minus_bitpos (rtx ref, tree t, int objectp,
      the expression.  */
   if (! TYPE_P (t))
     {
-      tree base = get_base_address (t);
-      if (base && DECL_P (base)
-	  && TREE_READONLY (base)
-	  && (TREE_STATIC (base) || DECL_EXTERNAL (base)))
-	{
-	  tree base_type = TREE_TYPE (base);
-	  gcc_assert (!(base_type && TYPE_NEEDS_CONSTRUCTING (base_type))
-		      || DECL_ARTIFICIAL (base));
-	  MEM_READONLY_P (ref) = 1;
-	}
+      tree base;
 
       if (TREE_THIS_VOLATILE (t))
 	MEM_VOLATILE_P (ref) = 1;
@@ -1522,6 +1512,36 @@ set_mem_attributes_minus_bitpos (rtx ref, tree t, int objectp,
 	     || TREE_CODE (t) == SAVE_EXPR)
 	t = TREE_OPERAND (t, 0);
 
+      /* We may look through structure-like accesses for the purposes of
+	 examining TREE_THIS_NOTRAP, but not array-like accesses.  */
+      base = t;
+      while (TREE_CODE (base) == COMPONENT_REF
+	     || TREE_CODE (base) == REALPART_EXPR
+	     || TREE_CODE (base) == IMAGPART_EXPR
+	     || TREE_CODE (base) == BIT_FIELD_REF)
+	base = TREE_OPERAND (base, 0);
+
+      if (DECL_P (base))
+	{
+	  if (CODE_CONTAINS_STRUCT (TREE_CODE (base), TS_DECL_WITH_VIS))
+	    MEM_NOTRAP_P (ref) = !DECL_WEAK (base);
+	  else
+	    MEM_NOTRAP_P (ref) = 1;
+	}
+      else
+	MEM_NOTRAP_P (ref) = TREE_THIS_NOTRAP (base);
+
+      base = get_base_address (base);
+      if (base && DECL_P (base)
+	  && TREE_READONLY (base)
+	  && (TREE_STATIC (base) || DECL_EXTERNAL (base)))
+	{
+	  tree base_type = TREE_TYPE (base);
+	  gcc_assert (!(base_type && TYPE_NEEDS_CONSTRUCTING (base_type))
+		      || DECL_ARTIFICIAL (base));
+	  MEM_READONLY_P (ref) = 1;
+	}
+
       /* If this expression uses it's parent's alias set, mark it such
 	 that we won't change it.  */
       if (component_uses_parent_alias_set (t))