MS ABI x64: Pass small objects with dtors but no copy ctors directly

Passing objects directly (in registers or memory) creates a second copy
of the object in the callee.  The callee always destroys its copy, but
we also have to destroy any temporary created in the caller.  In other
words, copy elision of these kinds of objects is impossible.

Objects larger than 8 bytes with non-trivial dtors and trivial copy
ctors are still passed indirectly, and we can still elide copies of
them.

Fixes PR19640.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@207889 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/CGCall.cpp b/lib/CodeGen/CGCall.cpp
index 4428b9631626d8f0d0092d54e7205be468b7573f..da504739836a994345257f5ded66c1e5ae6c698e 100644 (file)
--- a/lib/CodeGen/CGCall.cpp
+++ b/lib/CodeGen/CGCall.cpp
@@ -2289,20 +2289,25 @@ void CodeGenFunction::EmitCallArg(CallArgList &args, const Expr *E,
   if (HasAggregateEvalKind &&
       CGM.getTarget().getCXXABI().areArgsDestroyedLeftToRightInCallee()) {
     // If we're using inalloca, use the argument memory.  Otherwise, use a
-    // temporary.  Either way, the aggregate is destroyed externally in the
-    // callee.
+    // temporary.
     AggValueSlot Slot;
     if (args.isUsingInAlloca())
       Slot = createPlaceholderSlot(*this, type);
     else
       Slot = CreateAggTemp(type, "agg.tmp");
-    Slot.setExternallyDestructed();
+
+    const CXXRecordDecl *RD = type->getAsCXXRecordDecl();
+    bool DestroyedInCallee =
+        RD && RD->hasNonTrivialDestructor() &&
+        CGM.getCXXABI().getRecordArgABI(RD) != CGCXXABI::RAA_Default;
+    if (DestroyedInCallee)
+      Slot.setExternallyDestructed();
+
     EmitAggExpr(E, Slot);
     RValue RV = Slot.asRValue();
     args.add(RV, type);
 
-    const CXXRecordDecl *RD = type->getAsCXXRecordDecl();
-    if (RD && RD->hasNonTrivialDestructor()) {
+    if (DestroyedInCallee) {
       // Create a no-op GEP between the placeholder and the cleanup so we can
       // RAUW it successfully.  It also serves as a marker of the first
       // instruction where the cleanup is active.

diff --git a/lib/CodeGen/MicrosoftCXXABI.cpp b/lib/CodeGen/MicrosoftCXXABI.cpp
index 869734ab4e49dece4babc6f244210a4e39441210..f22b96a6a07601de06d648881b6fb0b289a01d4c 100644 (file)
--- a/lib/CodeGen/MicrosoftCXXABI.cpp
+++ b/lib/CodeGen/MicrosoftCXXABI.cpp
@@ -44,17 +44,7 @@ public:
     return !RD->isPOD();
   }
 
-  RecordArgABI getRecordArgABI(const CXXRecordDecl *RD) const override {
-    if (RD->hasNonTrivialCopyConstructor() || RD->hasNonTrivialDestructor()) {
-      llvm::Triple::ArchType Arch = CGM.getTarget().getTriple().getArch();
-      if (Arch == llvm::Triple::x86)
-        return RAA_DirectInMemory;
-      // On x64, pass non-trivial records indirectly.
-      // FIXME: Test other Windows architectures.
-      return RAA_Indirect;
-    }
-    return RAA_Default;
-  }
+  RecordArgABI getRecordArgABI(const CXXRecordDecl *RD) const override;
 
   StringRef GetPureVirtualCallName() override { return "_purecall"; }
   // No known support for deleted functions in MSVC yet, so this choice is
@@ -407,6 +397,33 @@ private:
 
 }
 
+CGCXXABI::RecordArgABI
+MicrosoftCXXABI::getRecordArgABI(const CXXRecordDecl *RD) const {
+  switch (CGM.getTarget().getTriple().getArch()) {
+  default:
+    // FIXME: Implement for other architectures.
+    return RAA_Default;
+
+  case llvm::Triple::x86:
+    // 32-bit x86 constructs non-trivial objects directly in outgoing argument
+    // slots.  LLVM uses the inalloca attribute to implement this.
+    if (RD->hasNonTrivialCopyConstructor() || RD->hasNonTrivialDestructor())
+      return RAA_DirectInMemory;
+    return RAA_Default;
+
+  case llvm::Triple::x86_64:
+    // Win64 passes objects with non-trivial copy ctors indirectly.
+    if (RD->hasNonTrivialCopyConstructor())
+      return RAA_Indirect;
+    // Win64 passes objects larger than 8 bytes indirectly.
+    if (getContext().getTypeSize(RD->getTypeForDecl()) > 64)
+      return RAA_Indirect;
+    return RAA_Default;
+  }
+
+  llvm_unreachable("invalid enum");
+}
+
 llvm::Value *MicrosoftCXXABI::adjustToCompleteObject(CodeGenFunction &CGF,
                                                      llvm::Value *ptr,
                                                      QualType type) {

diff --git a/test/CodeGenCXX/microsoft-abi-arg-order.cpp b/test/CodeGenCXX/microsoft-abi-arg-order.cpp
index d26a515c85e59bf93d7846f253d4d0c9dab9b477..b47508b302d1c84a867494e44944281790fddb89 100644 (file)
--- a/test/CodeGenCXX/microsoft-abi-arg-order.cpp
+++ b/test/CodeGenCXX/microsoft-abi-arg-order.cpp
@@ -3,6 +3,7 @@
 
 struct A {
   A(int a);
+  A(const A &o);
   ~A();
   int a;
 };

diff --git a/test/CodeGenCXX/microsoft-abi-sret-and-byval.cpp b/test/CodeGenCXX/microsoft-abi-sret-and-byval.cpp
index bc937491a57635a077261538bd99422c777bdc06..1e333664c8b946192d259f21abe81eda4c635365 100644 (file)
--- a/test/CodeGenCXX/microsoft-abi-sret-and-byval.cpp
+++ b/test/CodeGenCXX/microsoft-abi-sret-and-byval.cpp
@@ -47,6 +47,12 @@ struct Big {
   int a, b, c, d, e, f;
 };
 
+struct BigWithDtor {
+  BigWithDtor();
+  ~BigWithDtor();
+  int a, b, c, d, e, f;
+};
+
 // WIN32: declare void @"{{.*take_bools_and_chars.*}}"
 // WIN32:       (<{ i8, [3 x i8], i8, [3 x i8], %struct.SmallWithDtor,
 // WIN32:           i8, [3 x i8], i8, [3 x i8], i32, i8, [3 x i8] }>* inalloca)
@@ -114,15 +120,43 @@ void small_arg_with_dtor(SmallWithDtor s) {}
 // WIN32: define void @"\01?small_arg_with_dtor@@YAXUSmallWithDtor@@@Z"(<{ %struct.SmallWithDtor }>* inalloca) {{.*}} {
 // WIN32:   call x86_thiscallcc void @"\01??1SmallWithDtor@@QAE@XZ"
 // WIN32: }
-// WIN64: define void @"\01?small_arg_with_dtor@@YAXUSmallWithDtor@@@Z"(%struct.SmallWithDtor* %s) {{.*}} {
+// WIN64: define void @"\01?small_arg_with_dtor@@YAXUSmallWithDtor@@@Z"(i32 %s.coerce) {{.*}} {
 // WIN64:   call void @"\01??1SmallWithDtor@@QEAA@XZ"
 // WIN64: }
 
+void call_small_arg_with_dtor() {
+  small_arg_with_dtor(SmallWithDtor());
+}
+// The temporary is copied, so it's destroyed in the caller as well as the
+// callee.
+// WIN64-LABEL: define void @"\01?call_small_arg_with_dtor@@YAXXZ"()
+// WIN64:   call %struct.SmallWithDtor* @"\01??0SmallWithDtor@@QEAA@XZ"
+// WIN64:   call void @"\01?small_arg_with_dtor@@YAXUSmallWithDtor@@@Z"(i32 %{{.*}})
+// WIN64:   call void @"\01??1SmallWithDtor@@QEAA@XZ"
+// WIN64:   ret void
+
 // Test that references aren't destroyed in the callee.
 void ref_small_arg_with_dtor(const SmallWithDtor &s) { }
 // WIN32: define void @"\01?ref_small_arg_with_dtor@@YAXABUSmallWithDtor@@@Z"(%struct.SmallWithDtor* %s) {{.*}} {
 // WIN32-NOT:   call x86_thiscallcc void @"\01??1SmallWithDtor@@QAE@XZ"
 // WIN32: }
+// WIN64-LABEL: define void @"\01?ref_small_arg_with_dtor@@YAXAEBUSmallWithDtor@@@Z"(%struct.SmallWithDtor* %s)
+
+void big_arg_with_dtor(BigWithDtor s) {}
+// WIN64-LABEL: define void @"\01?big_arg_with_dtor@@YAXUBigWithDtor@@@Z"(%struct.BigWithDtor* %s)
+// WIN64:   call void @"\01??1BigWithDtor@@QEAA@XZ"
+// WIN64: }
+
+void call_big_arg_with_dtor() {
+  big_arg_with_dtor(BigWithDtor());
+}
+// We can elide the copy of the temporary in the caller, because this object is
+// larger than 8 bytes and is passed indirectly.
+// WIN64-LABEL: define void @"\01?call_big_arg_with_dtor@@YAXXZ"()
+// WIN64:   call %struct.BigWithDtor* @"\01??0BigWithDtor@@QEAA@XZ"
+// WIN64:   call void @"\01?big_arg_with_dtor@@YAXUBigWithDtor@@@Z"(%struct.BigWithDtor* %{{.*}})
+// WIN64-NOT: call void @"\01??1BigWithDtor@@QEAA@XZ"
+// WIN64:   ret void
 
 // Test that temporaries passed by reference are destroyed in the caller.
 void temporary_ref_with_dtor() {