PR tree-optimization/35468

	* tree-ssa-ccp.c (fold_stmt_r): Don't fold reads from constant
	string on LHS.

	* gcc.dg/pr35468.c: New test.
	* gcc.c-torture/compile/pr35468.c: New test.


git-svn-id: https://gcc.gnu.org/svn/gcc/trunk@142598 138bc75d-0d04-0410-961f-82ee72b054a4

5 files changed, 36 insertions, 2 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index ae10870ed4f..9c9ad1f199b 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+2008-12-09  Jakub Jelinek  <jakub@redhat.com>
+
+	PR tree-optimization/35468
+	* tree-ssa-ccp.c (fold_stmt_r): Don't fold reads from constant
+	string on LHS.
+
 2008-12-09  Richard Guenther  <rguenther@suse.de>
 
 	PR tree-optimization/38445
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 07c5eb0c8ef..7cb6b4f2679 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,9 @@
+2008-12-09  Jakub Jelinek  <jakub@redhat.com>
+
+	PR tree-optimization/35468
+	* gcc.dg/pr35468.c: New test.
+	* gcc.c-torture/compile/pr35468.c: New test.
+
 2008-12-08  Jason Merrill  <jason@redhat.com>
 
 	PR c++/38410
diff --git a/gcc/testsuite/gcc.c-torture/compile/pr35468.c b/gcc/testsuite/gcc.c-torture/compile/pr35468.c
new file mode 100644
index 00000000000..16d064b6222
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/compile/pr35468.c
@@ -0,0 +1,7 @@
+/* PR tree-optimization/35468 */
+
+void
+foo (void)
+{
+  *(char *) "c" = 'x';
+}
diff --git a/gcc/testsuite/gcc.dg/pr35468.c b/gcc/testsuite/gcc.dg/pr35468.c
new file mode 100644
index 00000000000..085c073070c
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr35468.c
@@ -0,0 +1,10 @@
+/* PR tree-optimization/35468 */
+/* { dg-do compile  }*/
+/* { dg-options "-O2 -fno-tree-dce" } */
+
+char *const f(void)
+{
+  char *const line = "/dev/ptyXX";
+  line[8] = 1;
+  return line;
+}
diff --git a/gcc/tree-ssa-ccp.c b/gcc/tree-ssa-ccp.c
index 82933f81914..0908d546f00 100644
--- a/gcc/tree-ssa-ccp.c
+++ b/gcc/tree-ssa-ccp.c
@@ -2191,6 +2191,9 @@ fold_stmt_r (tree *expr_p, int *walk_subtrees, void *data)
 
       t = maybe_fold_stmt_indirect (expr, TREE_OPERAND (expr, 0),
 				    integer_zero_node);
+      /* Avoid folding *"abc" = 5 into 'a' = 5.  */
+      if (wi->is_lhs && t && TREE_CODE (t) == INTEGER_CST)
+	t = NULL_TREE;
       if (!t
 	  && TREE_CODE (TREE_OPERAND (expr, 0)) == ADDR_EXPR)
 	/* If we had a good reason for propagating the address here,
@@ -2219,8 +2222,10 @@ fold_stmt_r (tree *expr_p, int *walk_subtrees, void *data)
 	 Otherwise we'd be wasting time.  */
     case ARRAY_REF:
       /* If we are not processing expressions found within an
-	 ADDR_EXPR, then we can fold constant array references.  */
-      if (!*inside_addr_expr_p)
+	 ADDR_EXPR, then we can fold constant array references.
+	 Don't fold on LHS either, to avoid folding "abc"[0] = 5
+	 into 'a' = 5.  */
+      if (!*inside_addr_expr_p && !wi->is_lhs)
 	t = fold_read_from_constant_string (expr);
       else
 	t = NULL;