X86: swiftailcc fix csr save list and register mask on i386

rdar://76160189

Author: aschwaighofer

llvm/lib/Target/X86/X86RegisterInfo.cpp

@@ -350,6 +350,8 @@ X86RegisterInfo::getCalleeSavedRegs(const MachineFunction *MF) const {
       return CSR_Win64_NoSSE_SaveList;
     return CSR_Win64_SaveList;
   case CallingConv::SwiftTail:
+    if (!Is64Bit)
+      return CSR_32_SaveList;
     return IsWin64 ? CSR_Win64_SwiftTail_SaveList : CSR_64_SwiftTail_SaveList;
   case CallingConv::X86_64_SysV:
     if (CallsEHReturn)
@@ -468,6 +470,8 @@ X86RegisterInfo::getCallPreservedMask(const MachineFunction &MF,
   case CallingConv::Win64:
     return CSR_Win64_RegMask;
   case CallingConv::SwiftTail:
+    if (!Is64Bit)
+      return CSR_32_RegMask;
     return IsWin64 ? CSR_Win64_SwiftTail_RegMask : CSR_64_SwiftTail_RegMask;
   case CallingConv::X86_64_SysV:
     return CSR_64_RegMask;

llvm/test/CodeGen/X86/swifttail-async-i386.ll

@@ -0,0 +1,12 @@
+; RUN: llc -mtriple=i386-apple-darwin %s -o - | FileCheck %s
+
+declare void @clobber()
+
+declare swifttailcc void @swifttail_callee()
+define swifttailcc void @swifttail() {
+; CHECK-LABEL: swifttail:
+; CHECK-NOT: %rbx
+  call void @clobber()
+  tail call swifttailcc void @swifttail_callee()
+  ret void
+}