[X86] Output cfi directives for saved XMM registers even if no GPRs are saved

[mstorsjo]

Summary

This makes sure that functions that only clobber xmm registers (on win64) also get the right cfi directives, if dwarf exceptions are enabled. (D39673 will allow users to enable dwarf on x86_64 on clang.)

[rnk]

Ouch, thanks for the fix, looks good.

lib/Target/X86/X86FrameLowering.cpp

     if (!HasFP && NumBytes) {
       // Define the current CFA rule to use the provided offset.
       assert(StackSize);
       BuildCFI(MBB, MBBI, DL, MCCFIInstruction::createDefCfaOffset(
                                   nullptr, -StackSize + stackGrowth));
     }
 
     // Emit DWARF info specifying the offsets of the callee-saved registers.
-    if (PushedRegs)
-      emitCalleeSavedFrameMoves(MBB, MBBI, DL);
+    emitCalleeSavedFrameMoves(MBB, MBBI, DL);
   }
 
   // X86 Interrupt handling function cannot assume anything about the direction
   // flag (DF in EFLAGS register). Clear this flag by creating "cld" instruction
   // in each prologue of interrupt handler function.
   //
   // FIXME: Create "cld" instruction only in these cases:
   // 1. The interrupt handling function uses any of the "rep" instructions.

test/CodeGen/X86/cfi-xmm.ll

+; RUN: llc -mtriple x86_64-w64-windows-gnu -filetype=asm -exception-model=dwarf -o - %s | FileCheck %s
+
+define void @_Z1fv() {
+entry:
+  tail call void asm sideeffect "", "~{xmm10},~{xmm15},~{dirflag},~{fpsr},~{flags}"()
+  ret void
+}
+
+; CHECK-LABEL: _Z1fv:
+; CHECK:   .cfi_startproc
+; CHECK:   subq    $40, %rsp
+; CHECK:   movaps  %xmm15, 16(%rsp)
+; CHECK:   movaps  %xmm10, (%rsp)
+; CHECK:   .cfi_def_cfa_offset 48
+; CHECK:   .cfi_offset %xmm10, -48
+; CHECK:   .cfi_offset %xmm15, -32
+; CHECK:   movaps  (%rsp), %xmm10
+; CHECK:   movaps  16(%rsp), %xmm15
+; CHECK:   addq    $40, %rsp
+; CHECK:   retq
+; CHECK:   .cfi_endproc