[PATCH] MS ABI: Use the proper type for inalloca args

[David Majnemer]

Hi rnk,

The definition of a type later in a translation unit may change it's
type from {}* to (%struct.foo*)*.  Earlier function definitions may use
the former while more recent definitions might use the later.  This is
fine until they interact with one another (like one calling the other).
In these cases, a bitcast is needed because the inalloca must match the
function call but the store to the lvalue which initializes the argument
slot has to match the rvalue's type.

This technique is along the same lines with what the other,
non-inalloca, codepaths perform.

This fixes PR19287.

http://llvm-reviews.chandlerc.com/D3224

Files:
  lib/CodeGen/CGCall.cpp
  test/CodeGenCXX/microsoft-abi-sret-and-byval.cpp

Index: lib/CodeGen/CGCall.cpp
===================================================================
--- lib/CodeGen/CGCall.cpp
+++ lib/CodeGen/CGCall.cpp
@@ -2603,6 +2603,13 @@
         // Store the RValue into the argument struct.
         llvm::Value *Addr =
             Builder.CreateStructGEP(ArgMemory, ArgInfo.getInAllocaFieldIndex());
+        unsigned AS = Addr->getType()->getPointerAddressSpace();
+        llvm::Type *MemType = ConvertTypeForMem(I->Ty)->getPointerTo(AS);
+        // There are some cases where a trivial bitcast is not avoidable.  The
+        // definition of a type later in a translation unit may change it's type
+        // from {}* to (%struct.foo*)*.
+        if (Addr->getType() != MemType)
+          Addr = Builder.CreateBitCast(Addr, MemType);
         LValue argLV = MakeAddrLValue(Addr, I->Ty, TypeAlign);
         EmitInitStoreOfNonAggregate(*this, RV, argLV);
       }
Index: test/CodeGenCXX/microsoft-abi-sret-and-byval.cpp
===================================================================
--- test/CodeGenCXX/microsoft-abi-sret-and-byval.cpp
+++ test/CodeGenCXX/microsoft-abi-sret-and-byval.cpp
@@ -263,3 +263,23 @@
 // WIN32: }
 
 }
+
+// We would crash here because the later definition of ForwardDeclare1 results
+// in a different IR type for the value we want to store.  However, the alloca's
+// type will use the argument type selected by fn1.
+struct ForwardDeclare1;
+
+typedef void (*FnPtr1)(ForwardDeclare1);
+void fn1(FnPtr1, SmallWithDtor) {}
+
+struct ForwardDeclare1 {};
+
+void fn2() { fn1(0, SmallWithDtor()); };
+// WIN32-LABEL: define void @"\01?fn2@@YAXXZ"
+// WIN32:   %[[argmem:[^ ]*]] = alloca inalloca [[argmem_ty:<{ {}\*, %struct.SmallWithDtor }>]]
+// WIN32:   getelementptr inbounds [[argmem_ty]]* %[[argmem]], i32 0, i32 1
+// WIN32:   call x86_thiscallcc %struct.SmallWithDtor* @"\01??0SmallWithDtor@@QAE at XZ"(%struct.SmallWithDtor* %0)
+// WIN32:   getelementptr inbounds [[argmem_ty]]* %[[argmem]], i32 0, i32 0
+// WIN32:   %[[addr:[^ ]*]] = bitcast {}** %1 to void [[dst_ty:\(%struct.ForwardDeclare1\*\)\*]]*
+// WIN32:   store void [[dst_ty]] null, void [[dst_ty]]* %[[addr]], align 4
+// WIN32:   call void @"\01?fn1@@YAXP6AXUForwardDeclare1@@@ZUSmallWithDtor@@@Z"([[argmem_ty]]* inalloca %[[argmem]])
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