Omit arguments of __builtin_object_size from the CFG.

This builtin does not actually evaluate its arguments for side effects,
so we shouldn't include them in the CFG. In the analyzer, rely on the
constant expression evaluator to get the proper semantics, at least for
now. (In the future, we could get ambitious and try to provide path-
sensitive size values.)

In theory, this does pose a problem for liveness analysis: a variable can
be used within the __builtin_object_size argument expression but not show
up as live. However, it is very unlikely that such a value would be used
to compute the object size and not used to access the object in some way.

<rdar://problem/14760817>

llvm-svn: 188679

1 files changed, 18 insertions, 1 deletions

diff --git a/clang/test/Analysis/builtin-functions.cpp b/clang/test/Analysis/builtin-functions.cpp
index 5c18665d0fd..72d5ad23b16 100644
--- a/clang/test/Analysis/builtin-functions.cpp
+++ b/clang/test/Analysis/builtin-functions.cpp
@@ -2,6 +2,23 @@
 
 void clang_analyzer_eval(bool);
 
-void test(int x) {
+void testAddressof(int x) {
   clang_analyzer_eval(&x == __builtin_addressof(x)); // expected-warning{{TRUE}}
 }
+
+void testSize() {
+  struct {
+    int x;
+    int y;
+    char z;
+  } object;
+  clang_analyzer_eval(__builtin_object_size(&object.y, 0) == sizeof(object) - sizeof(int)); // expected-warning{{TRUE}}
+
+  // Clang can't actually evaluate these builtin "calls", but importantly they don't actually evaluate the argument expression either.
+  int i = 0;
+  char buf[10];
+  clang_analyzer_eval(__builtin_object_size(&buf[i++], 0) == sizeof(buf)); // expected-warning{{FALSE}}
+  clang_analyzer_eval(__builtin_object_size(&buf[++i], 0) == sizeof(buf) - 1); // expected-warning{{FALSE}}
+
+  clang_analyzer_eval(i == 0); // expected-warning{{TRUE}}
+}