re PR tree-optimization/85244 (Bad optimisation with flexible array member (may be...

2018-04-06  Richard Biener  <rguenther@suse.de>

	PR middle-end/85244
	* tree-dfa.c (get_ref_base_and_extent): Reset seen_variable_array_ref
	after seeing a component reference with an adjacent field.  Treat
	refs to arrays at struct end of external decls similar to
	refs to unconstrained commons.

	* gcc.dg/torture/pr85244-1.c: New testcase.
	* gcc.dg/torture/pr85244-2.c: Likewise.

From-SVN: r259168

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 654a0aa28b4ac206b085235c98b6c22004045223..f95365232dcad423e38c5660009826e48fb4813f 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,11 @@
+2018-04-06  Richard Biener  <rguenther@suse.de>
+
+       PR middle-end/85244
+       * tree-dfa.c (get_ref_base_and_extent): Reset seen_variable_array_ref
+       after seeing a component reference with an adjacent field.  Treat
+       refs to arrays at struct end of external decls similar to
+       refs to unconstrained commons.
+
 2018-04-06  Jakub Jelinek  <jakub@redhat.com>
 
        PR sanitizer/85213

diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 60d0484fc6d98db0d61f6c29ffea4b96a15f46a8..e52b67c589c46109b422d53028e317fb5cb0103f 100644 (file)
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,9 @@
+2018-04-06  Richard Biener  <rguenther@suse.de>
+
+       PR middle-end/85244
+       * gcc.dg/torture/pr85244-1.c: New testcase.
+       * gcc.dg/torture/pr85244-2.c: Likewise.
+
 2018-04-06  Jakub Jelinek  <jakub@redhat.com>
 
        PR sanitizer/85213

diff --git a/gcc/testsuite/gcc.dg/torture/pr85244-1.c b/gcc/testsuite/gcc.dg/torture/pr85244-1.c
new file mode 100644 (file)
index 0000000..44716aa
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr85244-1.c
@@ -0,0 +1,19 @@
+/* { dg-do run } */
+/* { dg-additional-sources "pr85244-2.c" } */
+
+struct s {
+ long a;
+ int b;
+ int tab[];
+};
+
+extern const struct s val;
+extern int idx;
+extern void abort (void);
+
+int main()
+{
+  if (val.tab[0] != 42 || val.tab[1] != 1337 || val.tab[idx] != 1337)
+    abort ();
+  return 0;
+}

diff --git a/gcc/testsuite/gcc.dg/torture/pr85244-2.c b/gcc/testsuite/gcc.dg/torture/pr85244-2.c
new file mode 100644 (file)
index 0000000..d57cb71
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr85244-2.c
@@ -0,0 +1,8 @@
+struct s {
+    long a;
+    int b;
+    int tab[];
+};
+
+int idx = 1;
+const struct s val = { 0, 0, { 42, 1337 } };

diff --git a/gcc/tree-dfa.c b/gcc/tree-dfa.c
index b50b9abcd9e5f5573f52c0bb874d58b220837c89..a121b880bb045affa18a7c1101c9de2272f6bb14 100644 (file)
--- a/gcc/tree-dfa.c
+++ b/gcc/tree-dfa.c
@@ -438,7 +438,7 @@ get_ref_base_and_extent (tree exp, poly_int64_pod *poffset,
                   referenced the last field of a struct or a union member
                   then we have to adjust maxsize by the padding at the end
                   of our field.  */
-               if (seen_variable_array_ref && known_size_p (maxsize))
+               if (seen_variable_array_ref)
                  {
                    tree stype = TREE_TYPE (TREE_OPERAND (exp, 0));
                    tree next = DECL_CHAIN (field);
@@ -454,7 +454,7 @@ get_ref_base_and_extent (tree exp, poly_int64_pod *poffset,
                            || ssize == NULL
                            || !poly_int_tree_p (ssize))
                          maxsize = -1;
-                       else
+                       else if (known_size_p (maxsize))
                          {
                            poly_offset_int tem
                              = (wi::to_poly_offset (ssize)
@@ -464,6 +464,11 @@ get_ref_base_and_extent (tree exp, poly_int64_pod *poffset,
                            maxsize += tem;
                          }
                      }
+                   /* An component ref with an adjacent field up in the
+                      structure hierarchy constrains the size of any variable
+                      array ref lower in the access hierarchy.  */
+                   else
+                     seen_variable_array_ref = false;
                  }
              }
            else
@@ -622,7 +627,9 @@ get_ref_base_and_extent (tree exp, poly_int64_pod *poffset,
 
   if (DECL_P (exp))
     {
-      if (flag_unconstrained_commons && VAR_P (exp) && DECL_COMMON (exp))
+      if (VAR_P (exp)
+         && ((flag_unconstrained_commons && DECL_COMMON (exp))
+             || (DECL_EXTERNAL (exp) && seen_variable_array_ref)))
        {
          tree sz_tree = TYPE_SIZE (TREE_TYPE (exp));
          /* If size is unknown, or we have read to the end, assume there