[PAC][AArch64] Lower ptrauth constants in code (#96879)

This re-applies #94241 after fixing buildbot failure, see
https://lab.llvm.org/buildbot/#/builders/51/builds/570

According to standard, `constexpr` variables and `const` variables
initialized with constant expressions can be used in lambdas w/o
capturing - see https://en.cppreference.com/w/cpp/language/lambda.
However, MSVC used on buildkite seems to ignore that rule and does not
allow using such uncaptured variables in lambdas: we have "error C3493:
'Mask16' cannot be implicitly captured because no default capture mode
has been specified" - see
https://buildkite.com/llvm-project/github-pull-requests/builds/73238

Explicitly capturing such a variable, however, makes buildbot fail with
"error: lambda capture 'Mask16' is not required to be captured for this
use [-Werror,-Wunused-lambda-capture]" - see
https://lab.llvm.org/buildbot/#/builders/51/builds/570.

Fix both cases by using `0xffff` value directly instead of giving a name
to it.

Original PR description below.

Depends on #94240.

Define the following pseudos for lowering ptrauth constants in code:

- non-`extern_weak`:
  - no GOT load needed: `MOVaddrPAC` - similar to `MOVaddr`, with added
PAC;
  - GOT load needed: `LOADgotPAC` - similar to `LOADgot`, with added PAC;
- `extern_weak`: `LOADauthptrstatic` - similar to `LOADgot`, but use a
special stub slot named `sym$auth_ptr$key$disc` filled by dynamic linker
during relocation resolving instead of a GOT slot.

---------

Co-authored-by: Ahmed Bougacha <ahmed@bougacha.org>

1 files changed, 6 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/MachineVerifier.cpp b/llvm/lib/CodeGen/MachineVerifier.cpp
index 9ea238c..0c8a0f2 100644
--- a/llvm/lib/CodeGen/MachineVerifier.cpp
+++ b/llvm/lib/CodeGen/MachineVerifier.cpp
@@ -2066,6 +2066,12 @@ void MachineVerifier::verifyPreISelGenericInstruction(const MachineInstr *MI) {
       report("Dst operand 0 must be a pointer", MI);
     break;
   }
+  case TargetOpcode::G_PTRAUTH_GLOBAL_VALUE: {
+    const MachineOperand &AddrOp = MI->getOperand(1);
+    if (!AddrOp.isReg() || !MRI->getType(AddrOp.getReg()).isPointer())
+      report("addr operand must be a pointer", &AddrOp, 1);
+    break;
+  }
   default:
     break;
   }