2 files changed, 6 insertions, 12 deletions
diff --git a/llvm/lib/IR/Verifier.cpp b/llvm/lib/IR/Verifier.cpp
index eb4e5bde3df..0df257da4a4 100644
--- a/llvm/lib/IR/Verifier.cpp
+++ b/llvm/lib/IR/Verifier.cpp
@@ -1055,20 +1055,19 @@ void Verifier::visitFunction(const Function &F) {
           "Attribute 'builtin' can only be applied to a callsite.", &F);
 
   // Check that this function meets the restrictions on this calling convention.
+  // Sometimes varargs is used for perfectly forwarding thunks, so some of these
+  // restrictions can be lifted.
   switch (F.getCallingConv()) {
   default:
-    break;
   case CallingConv::C:
     break;
   case CallingConv::Fast:
   case CallingConv::Cold:
-  case CallingConv::X86_FastCall:
-  case CallingConv::X86_ThisCall:
   case CallingConv::Intel_OCL_BI:
   case CallingConv::PTX_Kernel:
   case CallingConv::PTX_Device:
-    Assert1(!F.isVarArg(),
-            "Varargs functions must have C calling conventions!", &F);
+    Assert1(!F.isVarArg(), "Calling convention does not support varargs or "
+                           "perfect forwarding!", &F);
     break;
   }
 
diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 7c0bfeef947..0972a034d90 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -3605,23 +3605,18 @@ bool X86::isOffsetSuitableForCodeModel(int64_t Offset, CodeModel::Model M,
 /// own arguments. Callee pop is necessary to support tail calls.
 bool X86::isCalleePop(CallingConv::ID CallingConv,
                       bool is64Bit, bool IsVarArg, bool TailCallOpt) {
-  if (IsVarArg)
-    return false;
-
   switch (CallingConv) {
   default:
     return false;
   case CallingConv::X86_StdCall:
-    return !is64Bit;
   case CallingConv::X86_FastCall:
-    return !is64Bit;
   case CallingConv::X86_ThisCall:
     return !is64Bit;
   case CallingConv::Fast:
-    return TailCallOpt;
   case CallingConv::GHC:
-    return TailCallOpt;
   case CallingConv::HiPE:
+    if (IsVarArg)
+      return false;
     return TailCallOpt;
   }
 }