re PR tree-optimization/49079 (Bogus constant folding)

2011-05-20  Richard Guenther  <rguenther@suse.de>

	PR tree-optimization/49079
	* tree-dfa.c (get_ref_base_and_extent): Handle view-converting
	MEM_REFs correctly for the trailing array access detection.
	Special case constants the same way as decls for overall size
	constraining.

	* gcc.dg/torture/pr49079.c: New testcase.

From-SVN: r173954

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index a14e54f3978aaae7609800fcc4f175b019ba899d..821c0dd18ce9b2a8f5249148eb80fc3e621eb584 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,11 @@
+2011-05-20  Richard Guenther  <rguenther@suse.de>
+
+       PR tree-optimization/49079
+       * tree-dfa.c (get_ref_base_and_extent): Handle view-converting
+       MEM_REFs correctly for the trailing array access detection.
+       Special case constants the same way as decls for overall size
+       constraining.
+
 2011-05-20  Uros Bizjak  <ubizjak@gmail.com>
 
        * config/i386/mingw32.h (OUTPUT_QUOTED_STRING): Fix macro

diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 5e2bffedcc67920f59d6c7e8303962f07e6c6cd1..2bdb809c11f6796790484aacef3e2b358ee85208 100644 (file)
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2011-05-20  Richard Guenther  <rguenther@suse.de>
+
+       PR tree-optimization/49079
+       * gcc.dg/torture/pr49079.c: New testcase.
+
 2011-05-20  Jakub Jelinek  <jakub@redhat.com>
 
        PR tree-optimization/49073

diff --git a/gcc/testsuite/gcc.dg/torture/pr49079.c b/gcc/testsuite/gcc.dg/torture/pr49079.c
new file mode 100644 (file)
index 0000000..1b53d3c
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr49079.c
@@ -0,0 +1,31 @@
+/* { dg-do run } */
+
+extern void abort (void);
+
+struct Ustr
+{
+  unsigned char data[1];
+};
+
+static unsigned int
+ustr_xi__embed_val_get(const unsigned char *data)
+{
+  return (unsigned int)data[0];
+}
+
+int __attribute__((noinline)) zero(void) { return 0; }
+
+static unsigned int
+ustr_len(const struct Ustr *s1)
+{
+  return ustr_xi__embed_val_get(s1->data + 1 + zero());
+}
+
+int
+main()
+{
+  if (ustr_len (((struct Ustr *) "\x01" "\x0002" "s2")) != 2)
+    abort ();
+
+  return 0;
+}

diff --git a/gcc/tree-dfa.c b/gcc/tree-dfa.c
index 70e3c1d35cdfc7dd0cccda6f5af5216f12af6622..9791bccecae676aa4575bdce43bb9329b21d5257 100644 (file)
--- a/gcc/tree-dfa.c
+++ b/gcc/tree-dfa.c
@@ -714,6 +714,7 @@ get_ref_base_and_extent (tree exp, HOST_WIDE_INT *poffset,
   tree size_tree = NULL_TREE;
   HOST_WIDE_INT bit_offset = 0;
   bool seen_variable_array_ref = false;
+  tree base_type;
 
   /* First get the final access size from just the outermost expression.  */
   if (TREE_CODE (exp) == COMPONENT_REF)
@@ -744,6 +745,8 @@ get_ref_base_and_extent (tree exp, HOST_WIDE_INT *poffset,
      and find the ultimate containing object.  */
   while (1)
     {
+      base_type = TREE_TYPE (exp);
+
       switch (TREE_CODE (exp))
        {
        case BIT_FIELD_REF:
@@ -931,9 +934,16 @@ get_ref_base_and_extent (tree exp, HOST_WIDE_INT *poffset,
      the array.  The simplest way to conservatively deal with this
      is to punt in the case that offset + maxsize reaches the
      base type boundary.  This needs to include possible trailing padding
-     that is there for alignment purposes.
+     that is there for alignment purposes.  */
+
+  if (seen_variable_array_ref
+      && maxsize != -1
+      && (!host_integerp (TYPE_SIZE (base_type), 1)
+         || (bit_offset + maxsize
+             == (signed) TREE_INT_CST_LOW (TYPE_SIZE (base_type)))))
+    maxsize = -1;
 
-     That is of course only true if the base object is not a decl.  */
+  /* In case of a decl or constant base object we can do better.  */
 
   if (DECL_P (exp))
     {
@@ -943,12 +953,14 @@ get_ref_base_and_extent (tree exp, HOST_WIDE_INT *poffset,
          && host_integerp (DECL_SIZE (exp), 1))
        maxsize = TREE_INT_CST_LOW (DECL_SIZE (exp)) - bit_offset;
     }
-  else if (seen_variable_array_ref
-          && maxsize != -1
-          && (!host_integerp (TYPE_SIZE (TREE_TYPE (exp)), 1)
-              || (bit_offset + maxsize
-                  == (signed) TREE_INT_CST_LOW (TYPE_SIZE (TREE_TYPE (exp))))))
-    maxsize = -1;
+  else if (CONSTANT_CLASS_P (exp))
+    {
+      /* If maxsize is unknown adjust it according to the size of the
+         base type constant.  */
+      if (maxsize == -1
+         && host_integerp (TYPE_SIZE (TREE_TYPE (exp)), 1))
+       maxsize = TREE_INT_CST_LOW (TYPE_SIZE (TREE_TYPE (exp))) - bit_offset;
+    }
 
   /* ???  Due to negative offsets in ARRAY_REF we can end up with
      negative bit_offset here.  We might want to store a zero offset