re PR c/83801 ([avr] String constant in __flash not put into .progmem)

	PR c/83801
	* c-tree.h (decl_constant_value_1): Add a bool argument.
	* c-typeck.c (decl_constant_value_1): Add IN_INIT argument, allow
	returning a CONSTRUCTOR if it is true.  Use error_operand_p.
	(decl_constant_value): Adjust caller.
	* c-fold.c (c_fully_fold_internal): If in_init, pass true to
	decl_constant_value_1 as IN_INIT.  Otherwise, punt if
	decl_constant_value returns initializer that has BLKmode or
	array type.
	(c_fully_fold_internal) <case COMPONENT_REF>: Fold if !lval.

	* gcc.dg/pr83801.c: New test.

From-SVN: r256608

gcc/c/ChangeLog

+2018-01-13  Jakub Jelinek  <jakub@redhat.com>
+
+	PR c/83801
+	* c-tree.h (decl_constant_value_1): Add a bool argument.
+	* c-typeck.c (decl_constant_value_1): Add IN_INIT argument, allow
+	returning a CONSTRUCTOR if it is true.  Use error_operand_p.
+	(decl_constant_value): Adjust caller.
+	* c-fold.c (c_fully_fold_internal): If in_init, pass true to
+	decl_constant_value_1 as IN_INIT.  Otherwise, punt if
+	decl_constant_value returns initializer that has BLKmode or
+	array type.
+	(c_fully_fold_internal) <case COMPONENT_REF>: Fold if !lval.
+
 2018-01-03  Richard Sandiford  <richard.sandiford@linaro.org>
 	    Alan Hayward  <alan.hayward@arm.com>
 	    David Sherwood  <david.sherwood@arm.com>

gcc/c/c-fold.c

@@ -168,9 +168,15 @@ c_fully_fold_internal (tree expr, bool in_init, bool *maybe_const_operands,
       if (VAR_P (expr) && !lval && (optimize || in_init))
 	{
 	  if (in_init)
-	    ret = decl_constant_value_1 (expr);
+	    ret = decl_constant_value_1 (expr, true);
 	  else
-	    ret = decl_constant_value (expr);
+	    {
+	      ret = decl_constant_value (expr);
+	      if (ret != expr
+		  && (TYPE_MODE (TREE_TYPE (ret)) == BLKmode
+		      || TREE_CODE (TREE_TYPE (ret)) == ARRAY_TYPE))
+		return expr;
+	    }
 	  /* Avoid unwanted tree sharing between the initializer and current
 	     function's body where the tree can be modified e.g. by the
 	     gimplifier.  */
@@ -264,6 +270,8 @@ c_fully_fold_internal (tree expr, bool in_init, bool *maybe_const_operands,
 	  TREE_READONLY (ret) = TREE_READONLY (expr);
 	  TREE_THIS_VOLATILE (ret) = TREE_THIS_VOLATILE (expr);
 	}
+      if (!lval)
+	ret = fold (ret);
       goto out;
 
     case ARRAY_REF:

gcc/c/c-tree.h

@@ -640,7 +640,7 @@ extern struct c_expr default_function_array_read_conversion (location_t,
 							     struct c_expr);
 extern struct c_expr convert_lvalue_to_rvalue (location_t, struct c_expr,
 					       bool, bool);
-extern tree decl_constant_value_1 (tree);
+extern tree decl_constant_value_1 (tree, bool);
 extern void mark_exp_read (tree);
 extern tree composite_type (tree, tree);
 extern tree build_component_ref (location_t, tree, tree, location_t);

gcc/c/c-typeck.c

@@ -1832,20 +1832,20 @@ c_size_in_bytes (const_tree type)
 /* Return either DECL or its known constant value (if it has one).  */
 
 tree
-decl_constant_value_1 (tree decl)
+decl_constant_value_1 (tree decl, bool in_init)
 {
   if (/* Note that DECL_INITIAL isn't valid for a PARM_DECL.  */
       TREE_CODE (decl) != PARM_DECL
       && !TREE_THIS_VOLATILE (decl)
       && TREE_READONLY (decl)
       && DECL_INITIAL (decl) != NULL_TREE
-      && TREE_CODE (DECL_INITIAL (decl)) != ERROR_MARK
+      && !error_operand_p (DECL_INITIAL (decl))
       /* This is invalid if initial value is not constant.
 	 If it has either a function call, a memory reference,
 	 or a variable, then re-evaluating it could give different results.  */
       && TREE_CONSTANT (DECL_INITIAL (decl))
       /* Check for cases where this is sub-optimal, even though valid.  */
-      && TREE_CODE (DECL_INITIAL (decl)) != CONSTRUCTOR)
+      && (in_init || TREE_CODE (DECL_INITIAL (decl)) != CONSTRUCTOR))
     return DECL_INITIAL (decl);
   return decl;
 }
@@ -1858,7 +1858,7 @@ decl_constant_value (tree decl)
 {
   /* Don't change a variable array bound or initial value to a constant
      in a place where a variable is invalid.  */
-  return current_function_decl ? decl_constant_value_1 (decl) : decl;
+  return current_function_decl ? decl_constant_value_1 (decl, false) : decl;
 }
 
 /* Convert the array expression EXP to a pointer.  */

gcc/testsuite/ChangeLog

+2018-01-13  Jakub Jelinek  <jakub@redhat.com>
+
+	PR c/83801
+	* gcc.dg/pr83801.c: New test.
+
 2018-01-13  Paul Thomas  <pault@gcc.gnu.org>
 
 	PR fortran/52162

gcc/testsuite/gcc.dg/pr83801.c

+/* PR c/83801 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-original" } */
+
+static const char a[] = "01234567890123456789012345678901234567890123456789012345678901234567890123456789";
+static const char b = a[27];
+struct S { const char c[30]; const char d[30]; };
+static const struct S e[] = { { "01234567890123456789012345678", "90123456789012345678901234567" },
+                              { "89012345678901234567890123456", "78901234567890123456789012345" } };
+static const char f = e[1].c[4];
+
+char
+foo (int i)
+{
+  return a[i];
+}
+
+char
+bar (int i)
+{
+  return e[0].d[i];
+}
+
+/* { dg-final { scan-tree-dump {a\[i]} "original" } } */
+/* { dg-final { scan-tree-dump-not {"01234567890123456789012345678901234567890123456789012345678901234567890123456789"\[i]} "original" } } */
+/* { dg-final { scan-tree-dump {e\[0]\.d\[i]} "original" } } */
+/* { dg-final { scan-tree-dump-not {"90123456789012345678901234567"\[i]} "original" } } */