[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, 23 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/MachineModuleInfoImpls.cpp b/llvm/lib/CodeGen/MachineModuleInfoImpls.cpp
index 9c3b31935f6d..f114f1ecc0ba 100644
--- a/llvm/lib/CodeGen/MachineModuleInfoImpls.cpp
+++ b/llvm/lib/CodeGen/MachineModuleInfoImpls.cpp
@@ -13,6 +13,7 @@
 
 #include "llvm/CodeGen/MachineModuleInfoImpls.h"
 #include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/STLExtras.h"
 #include "llvm/MC/MCSymbol.h"
 
 using namespace llvm;
@@ -41,3 +42,25 @@ MachineModuleInfoImpl::SymbolListTy MachineModuleInfoImpl::getSortedStubs(
   Map.clear();
   return List;
 }
+
+template <typename MachineModuleInfoTarget>
+static typename MachineModuleInfoTarget::AuthStubListTy getAuthGVStubListHelper(
+    DenseMap<MCSymbol *, typename MachineModuleInfoTarget::AuthStubInfo>
+        &AuthPtrStubs) {
+  typename MachineModuleInfoTarget::AuthStubListTy List(AuthPtrStubs.begin(),
+                                                        AuthPtrStubs.end());
+
+  if (!List.empty())
+    llvm::sort(List.begin(), List.end(),
+               [](const typename MachineModuleInfoTarget::AuthStubPairTy &LHS,
+                  const typename MachineModuleInfoTarget::AuthStubPairTy &RHS) {
+                 return LHS.first->getName() < RHS.first->getName();
+               });
+
+  AuthPtrStubs.clear();
+  return List;
+}
+
+MachineModuleInfoELF::AuthStubListTy MachineModuleInfoELF::getAuthGVStubList() {
+  return getAuthGVStubListHelper<MachineModuleInfoELF>(AuthPtrStubs);
+}