re PR rtl-optimization/11210 (optimizer drops conditional with typecast from…

re PR rtl-optimization/11210 (optimizer drops conditional with typecast from signed to unsigned char)

	PR optimization/11210
	* expr.c (handled_component_p) [NOP_EXPR]: Add ??? note
	about the behaviour with regard to bitfields.
	* fold-const (decode_field_reference): Record outermost type in
	case the expression is a NOP. Strip all NOPs. Set the signedness
	to that of the outermost type (if any) when the bitsize is equal
	to the size of the type.

From-SVN: r68823

gcc/ChangeLog

+2003-07-02  Eric Botcazou  <ebotcazou@libertysurf.fr>
+
+	PR optimization/11210
+	* expr.c (handled_component_p) [NOP_EXPR]: Add ??? note
+	about the behaviour with regard to bitfields.
+	* fold-const (decode_field_reference): Record outermost type in
+	case the expression is a NOP. Strip all NOPs. Set the signedness
+	to that of the outermost type (if any) when the bitsize is equal
+	to the size of the type.
+
 2003-07-02  Richard Sandiford  <rsandifo@redhat.com>
 
 	* config/mips/mips.md (addsi3): Remove workaround for adds of -32768.

gcc/expr.c

@@ -5903,6 +5903,9 @@ handled_component_p (tree t)
     case VIEW_CONVERT_EXPR:
       return 1;
 
+    /* ??? Sure they are handled, but get_inner_reference may return
+       a different PBITSIZE, depending upon whether the expression is
+       wrapped up in a NOP_EXPR or not, e.g. for bitfields.  */
     case NOP_EXPR:
     case CONVERT_EXPR:
       return (TYPE_MODE (TREE_TYPE (t))

gcc/fold-const.c

@@ -2625,6 +2625,7 @@ decode_field_reference (tree exp, HOST_WIDE_INT *pbitsize, HOST_WIDE_INT *pbitpo
 			enum machine_mode *pmode, int *punsignedp, int *pvolatilep,
 			tree *pmask, tree *pand_mask)
 {
+  tree outer_type = 0;
   tree and_mask = 0;
   tree mask, inner, offset;
   tree unsigned_type;
@@ -2636,6 +2637,13 @@ decode_field_reference (tree exp, HOST_WIDE_INT *pbitsize, HOST_WIDE_INT *pbitpo
   if (! INTEGRAL_TYPE_P (TREE_TYPE (exp)))
     return 0;
 
+  /* We are interested in the bare arrangement of bits, so strip everything
+     that doesn't affect the machine mode.  However, record the type of the
+     outermost expression if it may matter below.  */
+  if (TREE_CODE (exp) == NOP_EXPR
+      || TREE_CODE (exp) == CONVERT_EXPR
+      || TREE_CODE (exp) == NON_LVALUE_EXPR)
+    outer_type = TREE_TYPE (exp);
   STRIP_NOPS (exp);
 
   if (TREE_CODE (exp) == BIT_AND_EXPR)
@@ -2654,6 +2662,12 @@ decode_field_reference (tree exp, HOST_WIDE_INT *pbitsize, HOST_WIDE_INT *pbitpo
       || TREE_CODE (inner) == PLACEHOLDER_EXPR)
     return 0;
 
+  /* If the number of bits in the reference is the same as the bitsize of
+     the outer type, then the outer type gives the signedness. Otherwise
+     (in case of a small bitfield) the signedness is unchanged.  */
+  if (outer_type && *pbitsize == tree_low_cst (TYPE_SIZE (outer_type), 1))
+    *punsignedp = TREE_UNSIGNED (outer_type);
+
   /* Compute the mask to access the bitfield.  */
   unsigned_type = (*lang_hooks.types.type_for_size) (*pbitsize, 1);
   precision = TYPE_PRECISION (unsigned_type);