[llvm] [AArch64][PAC] Don't skip global legalization for AUTH_TCRETURN (PR #182513)

[Anatoly Trosinenko via llvm-commits]

================
@@ -0,0 +1,16 @@
+; RUN: llc --mattr=+pauth -filetype=asm < %s | FileCheck %s
+
+; CHECK:         adrp    x0, global
+; CHECK-NEXT:    add x0, x0, :lo12:global
+; CHECK-NEXT:    braaz   x0
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128-Fn32"
+target triple = "aarch64-unknown-linux-pauthtest"
+
+ at global = dso_local local_unnamed_addr global ptr null
+
+define dso_local void @foo() local_unnamed_addr {
+entry:
+  tail call void @global() [ "ptrauth"(i32 0, i64 0) ]
+  ret void
+}
----------------
atrosinenko wrote:

This test case looks over-reduced: if I understand the intention correctly, it looks like a rather strange way to express the following

```llvm
declare void @global()

define dso_local void @foo() local_unnamed_addr {
entry:
  tail call void @global() [ "ptrauth"(i32 0, i64 0) ]
  ret void
}
```

Though the latter is rejected by the verifier in the first place as a direct authenticated call:

```
Direct call cannot have a ptrauth bundle
  tail call void @global() [ "ptrauth"(i32 0, i64 0) ]
llc: error: '<stdin>': input module cannot be verified
```

https://github.com/llvm/llvm-project/pull/182513