commit a51c4077c553c8703832e56ba763428334af8150
author George Burgess IV <george.burgess.iv@gmail.com> Fri Oct 16 01:49:01 2015 +0000
committer George Burgess IV <george.burgess.iv@gmail.com> Fri Oct 16 01:49:01 2015 +0000
tree e29ca4feada7bfa4fc0a294638f304b3f3c74903
parent 59e847f997a4494c695c89068c4db34fb36de3ab

Make __builtin_object_size more conservative

r246877 made __builtin_object_size substantially more aggressive with
unknown bases if Type=1 or Type=3, which causes issues when we encounter
code like this:

struct Foo {
  int a;
  char str[1];
};

const char str[] = "Hello, World!";
struct Foo *f = (struct Foo *)malloc(sizeof(*f) + strlen(str));
strcpy(&f->str, str);

__builtin_object_size(&f->str, 1) would hand back 1, which is
technically correct given the type of Foo, but the type of Foo lies to
us about how many bytes are available in this case.

This patch adds support for this "writing off the end" idiom -- we now
answer conservatively when we're given the address of the very last
member in a struct.

Differential Revision: http://reviews.llvm.org/D12169

llvm-svn: 250488

clang/test/CodeGen/object-size.cpp

diff --git a/clang/test/CodeGen/object-size.cpp b/clang/test/CodeGen/object-size.cpp
index 1c9d1ae..81b44a5 100644
--- a/clang/test/CodeGen/object-size.cpp
+++ b/clang/test/CodeGen/object-size.cpp
@@ -28,3 +28,37 @@
   // CHECK: store i32 4
   gi = __builtin_object_size((char*)(B*)&c, 0);
 }
+
+// CHECK-LABEL: define void @_Z5test2v()
+void test2() {
+  struct A { char buf[16]; };
+  struct B : A {};
+  struct C { int i; B bs[1]; } *c;
+
+  // CHECK: call i64 @llvm.objectsize.i64.p0i8(i8* %{{.*}}, i1 false)
+  gi = __builtin_object_size(&c->bs[0], 0);
+  // CHECK: call i64 @llvm.objectsize.i64.p0i8(i8* %{{.*}}, i1 false)
+  gi = __builtin_object_size(&c->bs[0], 1);
+  // CHECK: call i64 @llvm.objectsize.i64.p0i8(i8* %{{.*}}, i1 true)
+  gi = __builtin_object_size(&c->bs[0], 2);
+  // CHECK: store i32 16
+  gi = __builtin_object_size(&c->bs[0], 3);
+
+  // CHECK: call i64 @llvm.objectsize.i64.p0i8(i8* %{{.*}}, i1 false)
+  gi = __builtin_object_size((A*)&c->bs[0], 0);
+  // CHECK: store i32 16
+  gi = __builtin_object_size((A*)&c->bs[0], 1);
+  // CHECK: call i64 @llvm.objectsize.i64.p0i8(i8* %{{.*}}, i1 true)
+  gi = __builtin_object_size((A*)&c->bs[0], 2);
+  // CHECK: store i32 16
+  gi = __builtin_object_size((A*)&c->bs[0], 3);
+
+  // CHECK: call i64 @llvm.objectsize.i64.p0i8(i8* %{{.*}}, i1 false)
+  gi = __builtin_object_size(&c->bs[0].buf[0], 0);
+  // CHECK: store i32 16
+  gi = __builtin_object_size(&c->bs[0].buf[0], 1);
+  // CHECK: call i64 @llvm.objectsize.i64.p0i8(i8* %{{.*}}, i1 true)
+  gi = __builtin_object_size(&c->bs[0].buf[0], 2);
+  // CHECK: store i32 16
+  gi = __builtin_object_size(&c->bs[0].buf[0], 3);
+}