[c++17] P0135R1: Guaranteed copy elision.

When an object of class type is initialized from a prvalue of the same type
(ignoring cv qualifications), use the prvalue to initialize the object directly
instead of inserting a redundant elidable call to a copy constructor.

llvm-svn: 288866

1 files changed, 81 insertions, 0 deletions

diff --git a/clang/test/CodeGenCXX/cxx1z-copy-omission.cpp b/clang/test/CodeGenCXX/cxx1z-copy-omission.cpp
new file mode 100644
index 00000000000..234e4b12589
--- /dev/null
+++ b/clang/test/CodeGenCXX/cxx1z-copy-omission.cpp
@@ -0,0 +1,81 @@
+// RUN: %clang_cc1 -std=c++1z -emit-llvm -triple x86_64-linux-gnu -o - %s | FileCheck %s
+
+struct A {
+  A(int);
+  A(A&&);
+  A(const A&);
+  ~A();
+
+  int arr[10];
+};
+
+A f();
+void h();
+
+// CHECK-LABEL: define {{.*}} @_Z1gv(
+void g() {
+  // CHECK: %[[A:.*]] = alloca
+  // CHECK-NOT: alloca
+  // CHECK-NOT: call
+  // CHECK: call {{.*}} @_Z1fv({{.*}}* sret %[[A]])
+  A a = A( A{ f() } );
+  // CHECK-NOT: call
+
+  // CHECK: call void @_Z1hv(
+  h();
+  // CHECK-NOT: call
+
+  // CHECK: call void @_ZN1AD1Ev({{.*}}* %[[A]])
+  // CHECK-NOT: call
+  // CHECK-LABEL: }
+}
+
+void f(A);
+
+// CHECK-LABEL: define {{.*}} @_Z1hv(
+void h() {
+  // CHECK: %[[A:.*]] = alloca
+  // CHECK-NOT: alloca
+  // CHECK-NOT: call
+
+  // CHECK: call {{.*}} @_Z1fv({{.*}}* sret %[[A]])
+  // CHECK-NOT: call
+  // CHECK: call {{.*}} @_Z1f1A({{.*}}* %[[A]])
+  f(f());
+  // CHECK-NOT: call
+  // CHECK: call void @_ZN1AD1Ev({{.*}}* %[[A]])
+
+  // CHECK: call void @_Z1hv(
+  h();
+
+  // CHECK-NOT: call
+  // CHECK-LABEL: }
+}
+
+// We still pass classes with trivial copy/move constructors and destructors in
+// registers, even if the copy is formally omitted.
+struct B {
+  B(int);
+  int n;
+};
+
+B fB();
+void fB(B);
+
+// CHECK-LABEL: define {{.*}} @_Z1iv(
+void i() {
+  // CHECK: %[[B:.*]] = alloca
+  // CHECK-NOT: alloca
+  // CHECK-NOT: call
+
+  // CHECK: %[[B_N:.*]] = call i32 @_Z2fBv()
+  // CHECK-NOT: call
+  // CHECK: store i32 %[[B_N]],
+  // CHECK-NOT: call
+  // CHECK: %[[B_N:.*]] = load i32
+  // CHECK-NOT: call
+  // CHECK: call void @_Z2fB1B(i32 %[[B_N]])
+  fB(fB());
+
+  // CHECK-LABEL: }
+}