Assume `__cxa_allocate_exception` returns an under-aligned memory on

Darwin if the version of libc++abi isn't new enough to include the fix
in r319123

This patch resurrects r264998, which was committed to work around a bug
in libc++abi that was causing _cxa_allocate_exception to return a memory
that wasn't double-word aligned.

http://lists.llvm.org/pipermail/cfe-commits/Week-of-Mon-20160328/154332.html

In addition, this patch makes clang issue a warning if the type of the
thrown object requires an alignment that is larger than the minimum
guaranteed by the target C++ runtime.

rdar://problem/49864414

Differential Revision: https://reviews.llvm.org/D61667

llvm-svn: 360404

2 files changed, 72 insertions, 4 deletions

diff --git a/clang/test/CodeGenCXX/eh.cpp b/clang/test/CodeGenCXX/eh.cpp
index d393ee13b1c..37b3d8faddd 100644
--- a/clang/test/CodeGenCXX/eh.cpp
+++ b/clang/test/CodeGenCXX/eh.cpp
@@ -1,5 +1,5 @@
-// RUN: %clang_cc1 -fcxx-exceptions -fexceptions -triple x86_64-apple-darwin -std=c++11 -emit-llvm %s -o - \
-// RUN:   | FileCheck %s
+// RUN: %clang_cc1 -fcxx-exceptions -fexceptions -triple x86_64-apple-macosx10.13.99 -std=c++11 -emit-llvm -o - %s | FileCheck --check-prefix=CHECK --check-prefix=UNALIGNED %s
+// RUN: %clang_cc1 -fcxx-exceptions -fexceptions -triple x86_64-apple-macosx10.14 -std=c++11 -emit-llvm -o - %s | FileCheck --check-prefix=CHECK --check-prefix=ALIGNED %s
 
 struct test1_D {
   double d;
@@ -13,7 +13,8 @@ void test1() {
 // CHECK:       [[EXNOBJ:%.*]] = call i8* @__cxa_allocate_exception(i64 8)
 // CHECK-NEXT:  [[EXN:%.*]] = bitcast i8* [[EXNOBJ]] to [[DSTAR:%[^*]*\*]]
 // CHECK-NEXT:  [[EXN2:%.*]] = bitcast [[DSTAR]] [[EXN]] to i8*
-// CHECK-NEXT:  call void @llvm.memcpy.p0i8.p0i8.i64(i8* align 16 [[EXN2]], i8* align 8 bitcast ([[DSTAR]] @d1 to i8*), i64 8, i1 false)
+// UNALIGNED-NEXT:  call void @llvm.memcpy.p0i8.p0i8.i64(i8* align 8 [[EXN2]], i8* align 8 bitcast ([[DSTAR]] @d1 to i8*), i64 8, i1 false)
+// ALIGNED-NEXT:  call void @llvm.memcpy.p0i8.p0i8.i64(i8* align 16 [[EXN2]], i8* align 8 bitcast ([[DSTAR]] @d1 to i8*), i64 8, i1 false)
 // CHECK-NEXT:  call void @__cxa_throw(i8* [[EXNOBJ]], i8* bitcast ({ i8*, i8* }* @_ZTI7test1_D to i8*), i8* null) [[NR:#[0-9]+]]
 // CHECK-NEXT:  unreachable
 
@@ -466,7 +467,8 @@ int foo() {
   // CHECK: [[T0:%.*]] = call i8* @__cxa_allocate_exception(i64 16)
   // CHECK-NEXT: [[T1:%.*]] = bitcast i8* [[T0]] to %"class.test17::DerivedException"*
   // CHECK-NEXT: [[T2:%.*]] = bitcast %"class.test17::DerivedException"* [[T1]] to i8*
-  // CHECK-NEXT: call void @llvm.memset.p0i8.i64(i8* align 16 [[T2]], i8 0, i64 16, i1 false)
+  // UNALIGNED-NEXT: call void @llvm.memset.p0i8.i64(i8* align 8 [[T2]], i8 0, i64 16, i1 false)
+  // ALIGNED-NEXT: call void @llvm.memset.p0i8.i64(i8* align 16 [[T2]], i8 0, i64 16, i1 false)
 }
 }
 
diff --git a/clang/test/SemaCXX/warn-overaligned-type-thrown.cpp b/clang/test/SemaCXX/warn-overaligned-type-thrown.cpp
new file mode 100644
index 00000000000..08010177836
--- /dev/null
+++ b/clang/test/SemaCXX/warn-overaligned-type-thrown.cpp
@@ -0,0 +1,66 @@
+// RUN: %clang_cc1 -triple x86_64-apple-macosx10.13.99 -verify -fsyntax-only -std=c++11 -fcxx-exceptions -fexceptions -DUNDERALIGNED %s
+// RUN: %clang_cc1 -triple arm64-apple-ios10 -verify -fsyntax-only -std=c++11 -fcxx-exceptions -fexceptions -DUNDERALIGNED %s
+// RUN: %clang_cc1 -triple arm64-apple-tvos10 -verify -fsyntax-only -std=c++11 -fcxx-exceptions -fexceptions -DUNDERALIGNED %s
+// RUN: %clang_cc1 -triple arm64-apple-watchos4 -verify -fsyntax-only -std=c++11 -fcxx-exceptions -fexceptions -DUNDERALIGNED %s
+// RUN: %clang_cc1 -triple x86_64-apple-macosx10.14 -verify -fsyntax-only -std=c++11 -fcxx-exceptions -fexceptions %s
+// RUN: %clang_cc1 -triple arm64-apple-ios12 -verify -fsyntax-only -std=c++11 -fcxx-exceptions -fexceptions %s
+// RUN: %clang_cc1 -triple arm64-apple-tvos12 -verify -fsyntax-only -std=c++11 -fcxx-exceptions -fexceptions %s
+// RUN: %clang_cc1 -triple arm64-apple-watchos5 -verify -fsyntax-only -std=c++11 -fcxx-exceptions -fexceptions %s
+// RUN: %clang_cc1 -triple arm-linux-gnueabi -verify -fsyntax-only -std=c++11 -fcxx-exceptions -fexceptions %s
+// RUN: %clang_cc1 -triple aarch64-linux-gnueabi -verify -fsyntax-only -std=c++11 -fcxx-exceptions -fexceptions %s
+// RUN: %clang_cc1 -triple mipsel-linux-gnu -verify -fsyntax-only -std=c++11 -fcxx-exceptions -fexceptions %s
+// RUN: %clang_cc1 -triple mips64el-linux-gnu -verify -fsyntax-only -std=c++11 -fcxx-exceptions -fexceptions %s
+// RUN: %clang_cc1 -triple wasm32-unknown-unknown -verify -fsyntax-only -std=c++11 -fcxx-exceptions -fexceptions %s
+// RUN: %clang_cc1 -triple wasm64-unknown-unknown -verify -fsyntax-only -std=c++11 -fcxx-exceptions -fexceptions %s
+// RUN: %clang_cc1 -triple x86_64-apple-macosx10.14 -verify -fsyntax-only -std=c++11 -fcxx-exceptions -fexceptions -Wno-underaligned-exception-object -DNODIAG %s
+// RUN: %clang_cc1 -triple x86_64-windows-msvc -verify -fsyntax-only -std=c++11 -fcxx-exceptions -fexceptions -DNODIAG %s
+
+struct S0 {
+  S0();
+  int m;
+};
+
+struct Overaligned1 {
+  Overaligned1();
+  int __attribute__((aligned(16))) m;
+};
+
+struct __attribute__((aligned(16))) Overaligned2 {
+  Overaligned2();
+  int m;
+};
+
+struct Overaligned3 {
+  Overaligned3();
+  int __attribute__((aligned(64))) m;
+};
+
+void test0() {
+  throw S0();
+}
+
+void test1() {
+  throw Overaligned1();
+}
+
+void test2() {
+  throw Overaligned2();
+}
+
+void test3() {
+  throw Overaligned3();
+}
+
+#if defined(NODIAG)
+// expected-no-diagnostics
+#elif defined(UNDERALIGNED)
+// expected-warning@-14 {{underaligned exception object thrown}}
+// expected-note@-15 {{(16 bytes) is larger than the supported alignment of C++ exception objects on this target (8 bytes)}}
+// expected-warning@-12 {{underaligned exception object thrown}}
+// expected-note@-13 {{(16 bytes) is larger than the supported alignment of C++ exception objects on this target (8 bytes)}}
+// expected-warning@-10 {{underaligned exception object thrown}}
+// expected-note@-11 {{(64 bytes) is larger than the supported alignment of C++ exception objects on this target (8 bytes)}}
+#else
+// expected-warning@-13 {{underaligned exception object thrown}}
+// expected-note@-14 {{(64 bytes) is larger than the supported alignment of C++ exception objects on this target (16 bytes)}}
+#endif