musttail: Only set the inreg flag for fastcall and vectorcall

Otherwise we'll attempt to forward ECX, EDX, and EAX for cdecl and
stdcall thunks, leaving us with no scratch registers for indirect call
targets.

Fixes PR22052.

llvm-svn: 225729

1 files changed, 16 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/CallingConvLower.cpp b/llvm/lib/CodeGen/CallingConvLower.cpp
index fbe8b7c10e6..034ffb34b9c 100644
--- a/llvm/lib/CodeGen/CallingConvLower.cpp
+++ b/llvm/lib/CodeGen/CallingConvLower.cpp
@@ -181,15 +181,28 @@ void CCState::AnalyzeCallResult(MVT VT, CCAssignFn Fn) {
   }
 }
 
+static bool isValueTypeInRegForCC(CallingConv::ID CC, MVT VT) {
+  if (VT.isVector())
+    return true; // Assume -msse-regparm might be in effect.
+  if (!VT.isInteger())
+    return false;
+  if (CC == CallingConv::X86_VectorCall || CC == CallingConv::X86_FastCall)
+    return true;
+  return false;
+}
+
 void CCState::getRemainingRegParmsForType(SmallVectorImpl<MCPhysReg> &Regs,
                                           MVT VT, CCAssignFn Fn) {
   unsigned SavedStackOffset = StackOffset;
   unsigned NumLocs = Locs.size();
 
-  // Allocate something of this value type repeatedly with just the inreg flag
-  // set until we get assigned a location in memory.
+  // Set the 'inreg' flag if it is used for this calling convention.
   ISD::ArgFlagsTy Flags;
-  Flags.setInReg();
+  if (isValueTypeInRegForCC(CallingConv, VT))
+    Flags.setInReg();
+
+  // Allocate something of this value type repeatedly until we get assigned a
+  // location in memory.
   bool HaveRegParm = true;
   while (HaveRegParm) {
     if (Fn(0, VT, VT, CCValAssign::Full, Flags, *this)) {