[PATCH] D24359: Win64: Don't use REX prefix for direct tail calls

[David Majnemer via llvm-commits]

majnemer added a comment.

Hmm, looks like we are over REXing there too:

  void __declspec(dllimport) h();
  void f() {
    h();
  }

turns into:

  f:                                      # @f
  .Ltmp0:
  .seh_proc f
  # BB#0:                                 # %entry
  .Ltmp1:
  	.seh_endprologue
  	rex64 jmpq	*__imp_h(%rip)  # TAILCALL
                                          # encoding: [0x48,0xff,0x25,A,A,A,A]
                                          #   fixup A - offset: 3, value: __imp_h-4, kind: reloc_riprel_4byte
  	.seh_handlerdata
  	.text
  .Ltmp2:
  	.seh_endproc

My reading indicates that the unwinder will consider this as a tail call.  If anything, our REX prefix is probably confusing it.

I imagine that MSVC omits it here?


https://reviews.llvm.org/D24359