Fix .cfi_restore with register numbers > 64

[arichardson]

Summary

DW_CFA_restore can only encode register numbers up to 64 (6 bits unsigned
int). For regsiter numbers > 64 we have to use DW_CFA_restore_extended
instead which uses a ULEB128 value.
I discovered this problem in the out-of-tree CHERI target since we use
DWARF register number 89 for our return capability register.

[JohnReagan]

Ah, thanks for finding this. We were just noticing this on our OpenVMS port since we also use platform-registers way up in the 16352-16383 range.

[dblaikie]

Seems pretty reasonable to me!

llvm/trunk/lib/MC/MCDwarf.cpp

case MCCFIInstruction::OpSameValue: {
     Streamer.EmitIntValue(dwarf::DW_CFA_same_value, 1);
     Streamer.EmitULEB128IntValue(Reg);
     return;
   }
   case MCCFIInstruction::OpRestore: {
     unsigned Reg = Instr.getRegister();
     if (!IsEH)
       Reg = MRI->getDwarfRegNumFromDwarfEHRegNum(Reg);
+    if (Reg < 64) {
       Streamer.EmitIntValue(dwarf::DW_CFA_restore | Reg, 1);
+    } else {
+      Streamer.EmitIntValue(dwarf::DW_CFA_restore_extended, 1);
+      Streamer.EmitULEB128IntValue(Reg);
+    }
     return;
   }
   case MCCFIInstruction::OpGnuArgsSize:
     Streamer.EmitIntValue(dwarf::DW_CFA_GNU_args_size, 1);
     Streamer.EmitULEB128IntValue(Instr.getOffset());
     return;
 
   case MCCFIInstruction::OpEscape:

llvm/trunk/test/MC/ELF/cfi-restore-extended.s

+// RUN: llvm-mc -filetype=obj -triple x86_64-pc-linux-gnu %s -o - | llvm-dwarfdump -debug-frame - | FileCheck %s
+
+// Check that register numbers greater than 63 can be used in .cfi_restore directives
+f:
+  .cfi_startproc
+  nop
+// CHECK: DW_CFA_advance_loc: 1
+  .cfi_restore %rbp
+// CHECK-NEXT: DW_CFA_restore: reg6
+  nop
+// CHECK-NEXT: DW_CFA_advance_loc: 1
+  .cfi_restore 89
+// CHECK-NEXT: DW_CFA_restore_extended: reg89
+// CHECK-NEXT: DW_CFA_nop:
+  nop
+  .cfi_endproc
+