[clang] [PAC] Add support for __ptrauth type qualifier (PR #100830)

[Daniil Kovalev via cfe-commits]

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@@ -166,6 +193,92 @@ CGPointerAuthInfo CodeGenModule::getPointerAuthInfoForType(QualType T) {
   return ::getPointerAuthInfoForType(*this, T);
 }
 
+static std::pair<llvm::Value *, CGPointerAuthInfo>
+emitLoadOfOrigPointerRValue(CodeGenFunction &CGF, const LValue &LV,
+                            SourceLocation Loc) {
+  auto *Value = CGF.EmitLoadOfScalar(LV, Loc);
+  CGPointerAuthInfo AuthInfo;
+  if (PointerAuthQualifier PtrAuth = LV.getQuals().getPointerAuth()) {
+    AuthInfo = CGF.EmitPointerAuthInfo(PtrAuth, LV.getAddress());
+  } else {
+    AuthInfo = getPointerAuthInfoForType(CGF.CGM, LV.getType());
+  }
+  return {Value, AuthInfo};
+}
+
+/// Retrieve a pointer rvalue and its ptrauth info. When possible, avoid
+/// needlessly resigning the pointer.
+std::pair<llvm::Value *, CGPointerAuthInfo>
+CodeGenFunction::EmitOrigPointerRValue(const Expr *E) {
+  assert(E->getType()->isSignableType());
+
+  E = E->IgnoreParens();
+  if (auto *Load = dyn_cast<ImplicitCastExpr>(E)) {
+    if (Load->getCastKind() == CK_LValueToRValue) {
+      E = Load->getSubExpr()->IgnoreParens();
+
+      // We're semantically required to not emit loads of certain DREs naively.
+      if (auto *RefExpr = dyn_cast<DeclRefExpr>(const_cast<Expr *>(E))) {
----------------
kovdan01 wrote:

I do not think that having a `const_cast` here is a good idea. I was able to transform this into

```suggestion
      if (const auto *RefExpr = dyn_cast<DeclRefExpr>(E)) {
```

by introducing the following changes:
- `CodeGenFunction::tryEmitAsConstant`: add `const` qualifier for `DeclRefExpr *` argument (and also add `const` inside the function where needed)
- `getReferenceLValue`: add `const` qualifier for `Expr *` argument

https://github.com/llvm/llvm-project/pull/100830