[ms-cxxabi] Use inalloca on win32 when passing non-trivial C++ objects

When a non-trivial parameter is present, clang now gathers up all the
parameters that lack inreg and puts them into a packed struct.  MSVC
always aligns each parameter to 4 bytes and no more, so this is a pretty
simple struct to lay out.

On win64, non-trivial records are passed indirectly.  Prior to this
change, clang was incorrectly using byval on win64.

I'm able to self-host a working clang with this change and additional
LLVM patches.

Reviewers: rsmith

Differential Revision: http://llvm-reviews.chandlerc.com/D2636

llvm-svn: 200597

1 files changed, 21 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/CGCall.h b/clang/lib/CodeGen/CGCall.h
index 532cb59c62e..c51f06fdcd2 100644
--- a/clang/lib/CodeGen/CGCall.h
+++ b/clang/lib/CodeGen/CGCall.h
@@ -56,6 +56,8 @@ namespace CodeGen {
   class CallArgList :
     public SmallVector<CallArg, 16> {
   public:
+    CallArgList() : StackBase(0), StackBaseMem(0) {}
+
     struct Writeback {
       /// The original argument.  Note that the argument l-value
       /// is potentially null.
@@ -113,6 +115,14 @@ namespace CodeGen {
       return CleanupsToDeactivate;
     }
 
+    void allocateArgumentMemory(CodeGenFunction &CGF);
+    llvm::Instruction *getStackBase() const { return StackBase; }
+    void freeArgumentMemory(CodeGenFunction &CGF) const;
+
+    /// \brief Returns if we're using an inalloca struct to pass arguments in
+    /// memory.
+    bool isUsingInAlloca() const { return StackBase; }
+
   private:
     SmallVector<Writeback, 1> Writebacks;
 
@@ -120,6 +130,17 @@ namespace CodeGen {
     /// is used to cleanup objects that are owned by the callee once the call
     /// occurs.
     SmallVector<CallArgCleanup, 1> CleanupsToDeactivate;
+
+    /// The stacksave call.  It dominates all of the argument evaluation.
+    llvm::CallInst *StackBase;
+
+    /// The alloca holding the stackbase.  We need it to maintain SSA form.
+    llvm::AllocaInst *StackBaseMem;
+
+    /// The iterator pointing to the stack restore cleanup.  We manually run and
+    /// deactivate this cleanup after the call in the unexceptional case because
+    /// it doesn't run in the normal order.
+    EHScopeStack::stable_iterator StackCleanup;
   };
 
   /// FunctionArgList - Type for representing both the decl and type