re PR c++/80129 (wrong code with ternary struct assignment to const)

PR c++/80129
	* gimplify.c (gimplify_modify_expr_rhs) <case COND_EXPR>: Clear
	TREE_READONLY on result if writing it more than once.

	* g++.dg/torture/pr80129.C: New test.

From-SVN: r246401

gcc/ChangeLog

@@ -1,5 +1,9 @@
 2017-03-22  Jakub Jelinek  <jakub@redhat.com>
 
+	PR c++/80129
+	* gimplify.c (gimplify_modify_expr_rhs) <case COND_EXPR>: Clear
+	TREE_READONLY on result if writing it more than once.
+
 	PR sanitizer/80110
 	* doc/invoke.texi (-fsanitize=thread): Document that with
 	-fnon-call-exceptions atomics are not able to throw

gcc/gimplify.c

@@ -5098,6 +5098,14 @@ gimplify_modify_expr_rhs (tree *expr_p, tree *from_p, tree *to_p,
 	      if (ret != GS_ERROR)
 		ret = GS_OK;
 
+	      /* If we are going to write RESULT more than once, clear
+		 TREE_READONLY flag, otherwise we might incorrectly promote
+		 the variable to static const and initialize it at compile
+		 time in one of the branches.  */
+	      if (VAR_P (result)
+		  && TREE_TYPE (TREE_OPERAND (cond, 1)) != void_type_node
+		  && TREE_TYPE (TREE_OPERAND (cond, 2)) != void_type_node)
+		TREE_READONLY (result) = 0;
 	      if (TREE_TYPE (TREE_OPERAND (cond, 1)) != void_type_node)
 		TREE_OPERAND (cond, 1)
 		  = build2 (code, void_type_node, result,

gcc/testsuite/ChangeLog

@@ -1,5 +1,8 @@
 2017-03-22  Jakub Jelinek  <jakub@redhat.com>
 
+	PR c++/80129
+	* g++.dg/torture/pr80129.C: New test.
+
 	PR sanitizer/80110
 	* g++.dg/tsan/pr80110.C: New test.
 

gcc/testsuite/g++.dg/torture/pr80129.C

@@ -0,0 +1,14 @@
+// PR c++/80129
+// { dg-do run }
+// { dg-options "-std=c++11" }
+
+struct A { bool a; int b; };
+
+int
+main ()
+{
+  bool c = false;
+  const A x = c ? A {true, 1} : A {false, 0};
+  if (x.a)
+    __builtin_abort ();
+}