MS ABI: Ensure 'this' is first for byval+sret methods

Previously we were building up the inalloca struct in the usual pattern
of return type followed by arguments.  However, on Windows, 'this'
always precedes the 'sret' parameter, so we need to insert it into the
struct first as a special case.

llvm-svn: 213990

1 files changed, 34 insertions, 21 deletions

diff --git a/clang/lib/CodeGen/TargetInfo.cpp b/clang/lib/CodeGen/TargetInfo.cpp
index 40fc51146aa..1a1ac8bd925 100644
--- a/clang/lib/CodeGen/TargetInfo.cpp
+++ b/clang/lib/CodeGen/TargetInfo.cpp
@@ -1002,6 +1002,26 @@ X86_32ABIInfo::addFieldToArgStruct(SmallVector<llvm::Type *, 6> &FrameFields,
   }
 }
 
+static bool isArgInAlloca(const ABIArgInfo &Info) {
+  // Leave ignored and inreg arguments alone.
+  switch (Info.getKind()) {
+  case ABIArgInfo::InAlloca:
+    return true;
+  case ABIArgInfo::Indirect:
+    assert(Info.getIndirectByVal());
+    return true;
+  case ABIArgInfo::Ignore:
+    return false;
+  case ABIArgInfo::Direct:
+  case ABIArgInfo::Extend:
+  case ABIArgInfo::Expand:
+    if (Info.getInReg())
+      return false;
+    return true;
+  }
+  llvm_unreachable("invalid enum");
+}
+
 void X86_32ABIInfo::rewriteWithInAlloca(CGFunctionInfo &FI) const {
   assert(IsWin32StructABI && "inalloca only supported on win32");
 
@@ -1009,9 +1029,19 @@ void X86_32ABIInfo::rewriteWithInAlloca(CGFunctionInfo &FI) const {
   SmallVector<llvm::Type *, 6> FrameFields;
 
   unsigned StackOffset = 0;
+  CGFunctionInfo::arg_iterator I = FI.arg_begin(), E = FI.arg_end();
 
-  // Put the sret parameter into the inalloca struct if it's in memory.
+  // Put 'this' into the struct before 'sret', if necessary.
+  bool IsThisCall =
+      FI.getCallingConvention() == llvm::CallingConv::X86_ThisCall;
   ABIArgInfo &Ret = FI.getReturnInfo();
+  if (Ret.isIndirect() && Ret.isSRetAfterThis() && !IsThisCall &&
+      isArgInAlloca(I->info)) {
+    addFieldToArgStruct(FrameFields, StackOffset, I->info, I->type);
+    ++I;
+  }
+
+  // Put the sret parameter into the inalloca struct if it's in memory.
   if (Ret.isIndirect() && !Ret.getInReg()) {
     CanQualType PtrTy = getContext().getPointerType(FI.getReturnType());
     addFieldToArgStruct(FrameFields, StackOffset, Ret, PtrTy);
@@ -1020,30 +1050,13 @@ void X86_32ABIInfo::rewriteWithInAlloca(CGFunctionInfo &FI) const {
   }
 
   // Skip the 'this' parameter in ecx.
-  CGFunctionInfo::arg_iterator I = FI.arg_begin(), E = FI.arg_end();
-  if (FI.getCallingConvention() == llvm::CallingConv::X86_ThisCall)
+  if (IsThisCall)
     ++I;
 
   // Put arguments passed in memory into the struct.
   for (; I != E; ++I) {
-
-    // Leave ignored and inreg arguments alone.
-    switch (I->info.getKind()) {
-    case ABIArgInfo::Indirect:
-      assert(I->info.getIndirectByVal());
-      break;
-    case ABIArgInfo::Ignore:
-      continue;
-    case ABIArgInfo::Direct:
-    case ABIArgInfo::Extend:
-      if (I->info.getInReg())
-        continue;
-      break;
-    default:
-      break;
-    }
-
-    addFieldToArgStruct(FrameFields, StackOffset, I->info, I->type);
+    if (isArgInAlloca(I->info))
+      addFieldToArgStruct(FrameFields, StackOffset, I->info, I->type);
   }
 
   FI.setArgStruct(llvm::StructType::get(getVMContext(), FrameFields,