Teach Expr::HasSideEffects about all the Expr types, and fix a bug where it

was mistakenly classifying dynamic_casts which might throw as having no side
effects.

Switch it from a visitor to a switch, so it is kept up-to-date as future Expr
nodes are added. Move it from ExprConstant.cpp to Expr.cpp, since it's not
really related to constant expression evaluation.

Since we use HasSideEffect to determine whether to emit an unused global with
internal linkage, this has the effect of suppressing emission of globals in
some cases.

I've left many of the Objective-C cases conservatively assuming that the
expression has side-effects. I'll leave it to someone with better knowledge
of Objective-C than mine to improve them.

llvm-svn: 161388

1 files changed, 82 insertions, 13 deletions

diff --git a/clang/test/CodeGenCXX/global-init.cpp b/clang/test/CodeGenCXX/global-init.cpp
index 8e6ef775cad..da5467ac3f4 100644
--- a/clang/test/CodeGenCXX/global-init.cpp
+++ b/clang/test/CodeGenCXX/global-init.cpp
@@ -70,17 +70,17 @@ namespace test3 {
   const char *test() { return var; }
 }
 
-namespace test6 {
+namespace test4 {
   struct A {
     A();
   };
   extern int foo();
 
   // This needs an initialization function and guard variables.
-  // CHECK: load i8* bitcast (i64* @_ZGVN5test61xE
-  // CHECK: [[CALL:%.*]] = call i32 @_ZN5test63fooEv
-  // CHECK-NEXT: store i32 [[CALL]], i32* @_ZN5test61xE
-  // CHECK-NEXT: store i64 1, i64* @_ZGVN5test61xE
+  // CHECK: load i8* bitcast (i64* @_ZGVN5test41xE
+  // CHECK: [[CALL:%.*]] = call i32 @_ZN5test43fooEv
+  // CHECK-NEXT: store i32 [[CALL]], i32* @_ZN5test41xE
+  // CHECK-NEXT: store i64 1, i64* @_ZGVN5test41xE
   __attribute__((weak)) int x = foo();
 }
 
@@ -95,14 +95,6 @@ namespace PR5974 {
   A* a = &c;
   B* b = &c;
 }
-// CHECK:      define internal void [[TEST1_Z_INIT:@.*]]()
-// CHECK:        load i32* @_ZN5test1L1yE
-// CHECK-NEXT:   xor
-// CHECK-NEXT:   store i32 {{.*}}, i32* @_ZN5test1L1zE
-// CHECK:      define internal void [[TEST1_Y_INIT:@.*]]()
-// CHECK:        load i32* @_ZN5test1L1xE
-// CHECK-NEXT:   sub
-// CHECK-NEXT:   store i32 {{.*}}, i32* @_ZN5test1L1yE
 
 // PR9570: the indirect field shouldn't crash IR gen.
 namespace test5 {
@@ -111,9 +103,86 @@ namespace test5 {
   };
 }
 
+namespace std { struct type_info; }
+
+namespace test6 {
+  struct A { virtual ~A(); };
+  struct B : A {};
+  extern A *p;
+
+  // We must emit a dynamic initializer for 'q', because it could throw.
+  B *const q = &dynamic_cast<B&>(*p);
+  // CHECK: call void @__cxa_bad_cast()
+  // CHECK: store {{.*}} @_ZN5test6L1qE
+
+  // We don't need to emit 'r' at all, because it has internal linkage, is
+  // unused, and its initialization has no side-effects.
+  B *const r = dynamic_cast<B*>(p);
+  // CHECK-NOT: call void @__cxa_bad_cast()
+  // CHECK-NOT: store {{.*}} @_ZN5test6L1rE
+
+  // This can throw, so we need to emit it.
+  const std::type_info *const s = &typeid(*p);
+  // CHECK: store {{.*}} @_ZN5test6L1sE
+
+  // This can't throw, so we don't.
+  const std::type_info *const t = &typeid(p);
+  // CHECK-NOT: @_ZN5test6L1tE
+
+  namespace {
+    int a = int();
+    volatile int b = int();
+    int c = a;
+    int d = b;
+    // CHECK-NOT: store {{.*}} @_ZN5test6{{[A-Za-z0-9_]*}}1aE
+    // CHECK-NOT: store {{.*}} @_ZN5test6{{[A-Za-z0-9_]*}}1bE
+    // CHECK-NOT: store {{.*}} @_ZN5test6{{[A-Za-z0-9_]*}}1cE
+    // CHECK: load volatile {{.*}} @_ZN5test6{{[A-Za-z0-9_]*}}1bE
+    // CHECK: store {{.*}} @_ZN5test6{{[A-Za-z0-9_]*}}1dE
+  }
+}
+
+namespace test7 {
+  struct A { A(); };
+  struct B { ~B(); int n; };
+  struct C { C() = default; C(const C&); };
+  struct D {};
+
+  // CHECK: call void @_ZN5test71AC1Ev({{.*}}@_ZN5test7L1aE)
+  const A a = A();
+
+  // CHECK: call i32 @__cxa_atexit({{.*}} @_ZN5test71BD1Ev{{.*}} @_ZN5test7L2b1E
+  // CHECK: call i32 @__cxa_atexit({{.*}} @_ZN5test71BD1Ev{{.*}} @_ZGRN5test72b2E
+  // CHECK: call void @_ZN5test71BD1Ev(
+  // CHECK: store {{.*}} @_ZN5test7L2b3E
+  const B b1 = B();
+  const B &b2 = B();
+  const int b3 = B().n;
+
+  // CHECK-NOT: @_ZN5test7L2c1E
+  // CHECK: @_ZN5test7L2c2E
+  const C c1 = C(); // elidable copy
+  const C c2 = static_cast<C&&>(C()); // non-elidable copy
+
+  // CHECK-NOT: @_ZN5test7L1dE
+  const D d = D();
+
+  // CHECK: store {{.*}} @_ZN5test71eE
+  int f(), e = f();
+}
+
 
 // At the end of the file, we check that y is initialized before z.
 
+// CHECK:      define internal void [[TEST1_Z_INIT:@.*]]()
+// CHECK:        load i32* @_ZN5test1L1yE
+// CHECK-NEXT:   xor
+// CHECK-NEXT:   store i32 {{.*}}, i32* @_ZN5test1L1zE
+// CHECK:      define internal void [[TEST1_Y_INIT:@.*]]()
+// CHECK:        load i32* @_ZN5test1L1xE
+// CHECK-NEXT:   sub
+// CHECK-NEXT:   store i32 {{.*}}, i32* @_ZN5test1L1yE
+
 // CHECK: define internal void @_GLOBAL__I_a() section "__TEXT,__StaticInit,regular,pure_instructions" {
 // CHECK:   call void [[TEST1_Y_INIT]]
 // CHECK:   call void [[TEST1_Z_INIT]]