X86: Assembly files with .cfi_cfa_def shouldn't hit llvm_unreachable()

On darwin, when trying to create compact unwind info, a .cfi_cfa_def
directive would case an llvm_unreachable() to be hit. Back off when we
see this directive and generate the regular DWARF style eh_frame.

rdar://15406518

llvm-svn: 194285

lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp

@@ -450,7 +450,9 @@ protected:
 
       switch (Inst.getOperation()) {
       default:
-        llvm_unreachable("cannot handle CFI directive for compact unwind!");
+        // Any other CFI directives indicate a frame that we aren't prepared
+        // to represent via compact unwind, so just bail out.
+        return 0;
       case MCCFIInstruction::OpDefCfaRegister: {
         // Defines a frame pointer. E.g.
         //

test/MC/X86/cfi_def_cfa-crash.s

@@ -0,0 +1,73 @@
+// RUN: llvm-mc -triple x86_64-apple-darwin -filetype=obj %s -o - | macho-dump | FileCheck %s
+
+// We were trying to generate compact unwind info for assembly like this.
+// The .cfi_def_cfa directive, however, throws a wrench into that and was
+// causing an llvm_unreachable() failure. Make sure the assembler can handle
+// the input. The actual eh_frames created using these directives are checked
+// elsewhere. This test is a simpler "does the code assemble" check.
+
+// rdar://15406518
+
+.macro SaveRegisters
+
+ push %rbp
+ .cfi_def_cfa_offset 16
+ .cfi_offset rbp, -16
+
+ mov %rsp, %rbp
+ .cfi_def_cfa_register rbp
+
+ sub $$0x80+8, %rsp
+
+ movdqa %xmm0, -0x80(%rbp)
+ push %rax
+ movdqa %xmm1, -0x70(%rbp)
+ push %rdi
+ movdqa %xmm2, -0x60(%rbp)
+ push %rsi
+ movdqa %xmm3, -0x50(%rbp)
+ push %rdx
+ movdqa %xmm4, -0x40(%rbp)
+ push %rcx
+ movdqa %xmm5, -0x30(%rbp)
+ push %r8
+ movdqa %xmm6, -0x20(%rbp)
+ push %r9
+ movdqa %xmm7, -0x10(%rbp)
+
+.endmacro
+.macro RestoreRegisters
+
+ movdqa -0x80(%rbp), %xmm0
+ pop %r9
+ movdqa -0x70(%rbp), %xmm1
+ pop %r8
+ movdqa -0x60(%rbp), %xmm2
+ pop %rcx
+ movdqa -0x50(%rbp), %xmm3
+ pop %rdx
+ movdqa -0x40(%rbp), %xmm4
+ pop %rsi
+ movdqa -0x30(%rbp), %xmm5
+ pop %rdi
+ movdqa -0x20(%rbp), %xmm6
+ pop %rax
+ movdqa -0x10(%rbp), %xmm7
+
+ leave
+ .cfi_def_cfa rsp, 8
+ .cfi_same_value rbp
+
+.endmacro
+
+_foo:
+.cfi_startproc
+  SaveRegisters
+
+  RestoreRegisters
+  ret
+ .cfi_endproc
+
+
+
+// CHECK: 'section_name', '__eh_frame\x00