[PATCH v2 4/4] tree-object-size: Fall back to wholesize for non-const offset

[Siddhesh Poyarekar]

Don't bail out early if the offset to a pointer in __builtin_object_size
is a variable, return the wholesize instead since that is a better
fallback for maximum estimate.  This should keep checks in place for
fortified functions to constrain overflows to at lesat some extent.

gcc/ChangeLog:

        PR middle-end/77608
        * tree-object-size.cc (plus_stmt_object_size): Drop check for
        constant offset.
        * testsuite/gcc.dg/builtin-object-size-1.c (test14): New test.

Signed-off-by: Siddhesh Poyarekar <siddh...@gotplt.org>
---
 gcc/testsuite/gcc.dg/builtin-object-size-1.c | 19 +++++++++++++++++++
 gcc/tree-object-size.cc                      |  7 ++++---
 2 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/gcc/testsuite/gcc.dg/builtin-object-size-1.c 
b/gcc/testsuite/gcc.dg/builtin-object-size-1.c
index 6ffe12be683..5a24087ae1e 100644
--- a/gcc/testsuite/gcc.dg/builtin-object-size-1.c
+++ b/gcc/testsuite/gcc.dg/builtin-object-size-1.c
@@ -791,6 +791,25 @@ test13 (unsigned cond)
 #endif
 }
 
+void
+__attribute__ ((noinline))
+test14 (unsigned off)
+{
+  char *buf2 = malloc (10);
+  char *p;
+  size_t t;
+
+  p = &buf2[off];
+
+#ifdef __builtin_object_size
+  if (__builtin_object_size (p, 0) != 10 - off)
+    FAIL ();
+#else
+  if (__builtin_object_size (p, 0) != 10)
+    FAIL ();
+#endif
+}
+
 int
 main (void)
 {
diff --git a/gcc/tree-object-size.cc b/gcc/tree-object-size.cc
index 1b569c3d12b..ebd2a4650aa 100644
--- a/gcc/tree-object-size.cc
+++ b/gcc/tree-object-size.cc
@@ -1595,8 +1595,7 @@ plus_stmt_object_size (struct object_size_info *osi, tree 
var, gimple *stmt)
     op1 = try_collapsing_offset (op1, NULL_TREE, NOP_EXPR, object_size_type);
 
   /* Handle PTR + OFFSET here.  */
-  if (size_valid_p (op1, object_size_type)
-      && (TREE_CODE (op0) == SSA_NAME || TREE_CODE (op0) == ADDR_EXPR))
+  if ((TREE_CODE (op0) == SSA_NAME || TREE_CODE (op0) == ADDR_EXPR))
     {
       if (TREE_CODE (op0) == SSA_NAME)
        {
@@ -1621,7 +1620,9 @@ plus_stmt_object_size (struct object_size_info *osi, tree 
var, gimple *stmt)
       if (size_unknown_p (bytes, 0))
        ;
       else if ((object_size_type & OST_DYNAMIC)
-              || bytes != wholesize || compare_tree_int (op1, offset_limit) <= 
0)
+              || bytes != wholesize
+              || (size_valid_p (op1, object_size_type)
+                  && compare_tree_int (op1, offset_limit) <= 0))
        bytes = size_for_offset (bytes, op1, wholesize);
       /* In the static case, with a negative offset, the best estimate for
         minimum size is size_unknown but for maximum size, the wholesize is a
-- 
2.45.1