[Target/X86] Don't use callee-saved registers in a Win64 tail call on non-Windows.

[cdavis5x]

Summary

A small bit that I missed when I updated the X86 backend to account for
the Win64 calling convention on non-Windows. Now we don't use dead
non-volatile registers when emitting a Win64 indirect tail call on
non-Windows.

Should fix PR23710.

[rnk]

Nice bug, lgtm. :)

lib/Target/X86/X86RegisterInfo.cpp

case 0: // Normal GPRs.
     if (Subtarget.isTarget64BitLP64())
       return &X86::GR64RegClass;
     return &X86::GR32RegClass;
   case 1: // Normal GPRs except the stack pointer (for encoding reasons).
     if (Subtarget.isTarget64BitLP64())
       return &X86::GR64_NOSPRegClass;
     return &X86::GR32_NOSPRegClass;
   case 2: // Available for tailcall (not callee-saved GPRs).
-    if (IsWin64)
+    const Function *F = MF.getFunction();
+    if (IsWin64 || (F && F->getCallingConv() == CallingConv::X86_64_Win64))
       return &X86::GR64_TCW64RegClass;
     else if (Is64Bit)
       return &X86::GR64_TCRegClass;
 
-    const Function *F = MF.getFunction();
     bool hasHipeCC = (F ? F->getCallingConv() == CallingConv::HiPE : false);
     if (hasHipeCC)
       return &X86::GR32RegClass;
     return &X86::GR32_TCRegClass;
   }
 }
 
 const TargetRegisterClass *

test/CodeGen/X86/sibcall-win64.ll

 ; RUN: llc < %s -mtriple=x86_64-pc-linux | FileCheck %s
 
 declare x86_64_win64cc void @win64_callee(i32)
+declare x86_64_win64cc void (i32)* @win64_indirect()
+declare x86_64_win64cc void @win64_other(i32)
 declare void @sysv_callee(i32)
+declare void (i32)* @sysv_indirect()
+declare void @sysv_other(i32)
 
 define void @sysv_caller(i32 %p1) {
 entry:
   tail call x86_64_win64cc void @win64_callee(i32 %p1)
   ret void
 }
 
 ; CHECK-LABEL: sysv_caller:

 
 define x86_64_win64cc void @win64_matched(i32 %p1) {
   tail call x86_64_win64cc void @win64_callee(i32 %p1)
   ret void
 }
 
 ; CHECK-LABEL: win64_matched:
 ; CHECK: jmp win64_callee # TAILCALL
+
+define x86_64_win64cc void @win64_indirect_caller(i32 %p1) {
+  %1 = call x86_64_win64cc void (i32)* @win64_indirect()
+  call x86_64_win64cc void @win64_other(i32 0)
+  tail call x86_64_win64cc void %1(i32 %p1)
+  ret void
+}
+
+; CHECK-LABEL: win64_indirect_caller:
+; CHECK: jmpq *%{{rax|rcx|rdx|r8|r9|r11}} # TAILCALL
+
+define void @sysv_indirect_caller(i32 %p1) {
+  %1 = call void (i32)* @sysv_indirect()
+  call void @sysv_other(i32 0)
+  tail call void %1(i32 %p1)
+  ret void
+}
+
+; CHECK-LABEL: sysv_indirect_caller:
+; CHECK: jmpq *%{{rax|rcx|rdx|rsi|rdi|r8|r9|r11}} # TAILCALL