[AArch64] Add test for DWARF return address signing

[pbarrio]

Summary

Patch by LukeCheeseman and pbarrio

[keith.walker.arm]

LGTM. Good to add missing tests for features that have been committed.

llvm/test/CodeGen/AArch64/sign-return-address-cfi-negate-ra-state.ll

+; RUN: llc -mtriple=aarch64-none-eabi < %s | FileCheck --check-prefixes CHECK,CHECK-V8A %s
+; RUN: llc -mtriple=aarch64-none-eabi -mattr=v8.3a < %s | FileCheck --check-prefixes CHECK,CHECK-V83A %s
+; RUN: llc -mtriple=aarch64-none-eabi -filetype=obj -o - <%s | llvm-dwarfdump -v - | FileCheck --check-prefix=CHECK-DUMP %s
+
+@.str = private unnamed_addr constant [15 x i8] c"some exception\00", align 1
+@_ZTIPKc = external dso_local constant i8*
+
+; CHECK: @_Z3fooi
+; CHECK-V8A: hint #25
+; CHECK-V83A: paciasp
+; CHECK-NEXT: .cfi_negate_ra_state
+; CHECK-NOT: .cfi_negate_ra_state
+define dso_local i32 @_Z3fooi(i32 %x) #0 {
+entry:
+  %retval = alloca i32, align 4
+  %x.addr = alloca i32, align 4
+  store i32 %x, i32* %x.addr, align 4
+  %exception = call i8* @__cxa_allocate_exception(i64 8) #1
+  %0 = bitcast i8* %exception to i8**
+  store i8* getelementptr inbounds ([15 x i8], [15 x i8]* @.str, i32 0, i32 0), i8** %0, align 16
+  call void @__cxa_throw(i8* %exception, i8* bitcast (i8** @_ZTIPKc to i8*), i8* null) #2
+  unreachable
+
+return:                                           ; No predecessors!
+  %1 = load i32, i32* %retval, align 4
+  ret i32 %1
+}
+
+declare dso_local i8* @__cxa_allocate_exception(i64)
+
+declare dso_local void @__cxa_throw(i8*, i8*, i8*)
+
+attributes #0 = { "sign-return-address"="all" }
+
+;CHECK-DUMP: DW_CFA_AARCH64_negate_ra_state