MS ABI: Use the correct this arg when generating implict copy ctor

We assumed that the incoming this argument would be the last argument.

However, this is not true under the MS ABI.

This fixes PR20897.

llvm-svn: 217642

4 files changed, 26 insertions, 4 deletions

diff --git a/clang/lib/CodeGen/CGCXXABI.h b/clang/lib/CodeGen/CGCXXABI.h
index fe331795e91..cf2cccd9910 100644
--- a/clang/lib/CodeGen/CGCXXABI.h
+++ b/clang/lib/CodeGen/CGCXXABI.h
@@ -384,6 +384,9 @@ public:
   virtual void EmitReturnFromThunk(CodeGenFunction &CGF,
                                    RValue RV, QualType ResultType);
 
+  virtual size_t getSrcArgforCopyCtor(const CXXConstructorDecl *,
+                                      FunctionArgList &Args) const = 0;
+
   /// Gets the pure virtual member call function.
   virtual StringRef GetPureVirtualCallName() = 0;
 
diff --git a/clang/lib/CodeGen/CGClass.cpp b/clang/lib/CodeGen/CGClass.cpp
index 1de325feea3..72869d8ca9b 100644
--- a/clang/lib/CodeGen/CGClass.cpp
+++ b/clang/lib/CodeGen/CGClass.cpp
@@ -914,11 +914,12 @@ namespace {
   private:
 
     /// Get source argument for copy constructor. Returns null if not a copy
-    /// constructor. 
-    static const VarDecl* getTrivialCopySource(const CXXConstructorDecl *CD,
+    /// constructor.
+    static const VarDecl *getTrivialCopySource(CodeGenFunction &CGF,
+                                               const CXXConstructorDecl *CD,
                                                FunctionArgList &Args) {
       if (CD->isCopyOrMoveConstructor() && CD->isDefaulted())
-        return Args[Args.size() - 1];
+        return Args[CGF.CGM.getCXXABI().getSrcArgforCopyCtor(CD, Args)];
       return nullptr;
     }
 
@@ -949,7 +950,7 @@ namespace {
   public:
     ConstructorMemcpyizer(CodeGenFunction &CGF, const CXXConstructorDecl *CD,
                           FunctionArgList &Args)
-      : FieldMemcpyizer(CGF, CD->getParent(), getTrivialCopySource(CD, Args)),
+      : FieldMemcpyizer(CGF, CD->getParent(), getTrivialCopySource(CGF, CD, Args)),
         ConstructorDecl(CD),
         MemcpyableCtor(CD->isDefaulted() &&
                        CD->isCopyOrMoveConstructor() &&
diff --git a/clang/lib/CodeGen/ItaniumCXXABI.cpp b/clang/lib/CodeGen/ItaniumCXXABI.cpp
index 25e2715daaf..bcc0f166203 100644
--- a/clang/lib/CodeGen/ItaniumCXXABI.cpp
+++ b/clang/lib/CodeGen/ItaniumCXXABI.cpp
@@ -208,6 +208,12 @@ public:
   llvm::Value *performReturnAdjustment(CodeGenFunction &CGF, llvm::Value *Ret,
                                        const ReturnAdjustment &RA) override;
 
+  size_t getSrcArgforCopyCtor(const CXXConstructorDecl *,
+                              FunctionArgList &Args) const override {
+    assert(!Args.empty() && "expected the arglist to not be empty!");
+    return Args.size() - 1;
+  }
+
   StringRef GetPureVirtualCallName() override { return "__cxa_pure_virtual"; }
   StringRef GetDeletedVirtualCallName() override
     { return "__cxa_deleted_virtual"; }
diff --git a/clang/lib/CodeGen/MicrosoftCXXABI.cpp b/clang/lib/CodeGen/MicrosoftCXXABI.cpp
index 173099a6bba..04b7ea08edc 100644
--- a/clang/lib/CodeGen/MicrosoftCXXABI.cpp
+++ b/clang/lib/CodeGen/MicrosoftCXXABI.cpp
@@ -50,6 +50,18 @@ public:
 
   bool isSRetParameterAfterThis() const override { return true; }
 
+  size_t getSrcArgforCopyCtor(const CXXConstructorDecl *CD,
+                              FunctionArgList &Args) const override {
+    assert(Args.size() >= 2 &&
+           "expected the arglist to have at least two args!");
+    // The 'most_derived' parameter goes second if the ctor is variadic and
+    // has v-bases.
+    if (CD->getParent()->getNumVBases() > 0 &&
+        CD->getType()->castAs<FunctionProtoType>()->isVariadic())
+      return 2;
+    return 1;
+  }
+
   StringRef GetPureVirtualCallName() override { return "_purecall"; }
   // No known support for deleted functions in MSVC yet, so this choice is
   // arbitrary.