[ubsan] Disable bounds-check for flexible array ivars

This eliminates a class of false positives for -fsanitize=array-bounds
on instrumented ObjC projects.

Differential Revision: https://reviews.llvm.org/D22227

llvm-svn: 283249

clang/lib/CodeGen/CGExpr.cpp

@@ -708,6 +708,8 @@ static bool isFlexibleArrayMemberExpr(const Expr *E) {
           DeclContext::decl_iterator(const_cast<FieldDecl *>(FD)));
       return ++FI == FD->getParent()->field_end();
     }
+  } else if (const auto *IRE = dyn_cast<ObjCIvarRefExpr>(E)) {
+    return IRE->getDecl()->getNextIvar() == nullptr;
   }
 
   return false;

clang/test/CodeGenObjC/ubsan-array-bounds.m

@@ -0,0 +1,59 @@
+// RUN: %clang_cc1 -x objective-c -emit-llvm -triple x86_64-apple-macosx10.10.0 -Wno-objc-root-class -fsanitize=array-bounds %s -o - | FileCheck %s
+
+@interface FlexibleArray1 {
+@public
+  char chars[0];
+}
+@end
+@implementation FlexibleArray1
+@end
+
+// CHECK-LABEL: test_FlexibleArray1
+char test_FlexibleArray1(FlexibleArray1 *FA1) {
+  // CHECK-NOT: !nosanitize
+  return FA1->chars[1];
+  // CHECK: }
+}
+
+@interface FlexibleArray2 {
+@public
+  char chars[0];
+}
+@end
+@implementation FlexibleArray2 {
+@public
+  char chars2[0];
+}
+@end
+
+// CHECK-LABEL: test_FlexibleArray2_1
+char test_FlexibleArray2_1(FlexibleArray2 *FA2) {
+  // CHECK: !nosanitize
+  return FA2->chars[1];
+  // CHECK: }
+}
+
+// CHECK-LABEL: test_FlexibleArray2_2
+char test_FlexibleArray2_2(FlexibleArray2 *FA2) {
+  // CHECK-NOT: !nosanitize
+  return FA2->chars2[1];
+  // CHECK: }
+}
+
+@interface FlexibleArray3 {
+@public
+  char chars[0];
+}
+@end
+@implementation FlexibleArray3 {
+@public
+  int i;
+}
+@end
+
+// CHECK-LABEL: test_FlexibleArray3
+char test_FlexibleArray3(FlexibleArray3 *FA3) {
+  // CHECK: !nosanitize
+  return FA3->chars[1];
+  // CHECK: }
+}