Fix .cfi_restore with register numbers > 64

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.

Reviewers: probinson, dblaikie, aprantl, espindola

Reviewed By: dblaikie

Subscribers: JohnReagan, emaste, JDevlieghere, llvm-commits

Differential Revision: https://reviews.llvm.org/D54420

llvm-svn: 346751

Author: arichardson

llvm/lib/MC/MCDwarf.cpp

@@ -1418,7 +1418,12 @@ void FrameEmitterImpl::EmitCFIInstruction(const MCCFIInstruction &Instr) {
     unsigned Reg = Instr.getRegister();
     if (!IsEH)
       Reg = MRI->getDwarfRegNumFromDwarfEHRegNum(Reg);
-    Streamer.EmitIntValue(dwarf::DW_CFA_restore | Reg, 1);
+    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:

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

@@ -0,0 +1,17 @@
+// 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
+