[clang] nonblocking/nonallocating attributes (was: nolock/noalloc) (PR #84983)

[Doug Wyatt via cfe-commits]

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@@ -7963,6 +7968,154 @@ static Attr *getCCTypeAttr(ASTContext &Ctx, ParsedAttr &Attr) {
   llvm_unreachable("unexpected attribute kind!");
 }
 
+std::optional<FunctionEffectMode>
+Sema::ActOnEffectExpression(Expr *CondExpr, StringRef AttributeName) {
+  auto BadExpr = [&]() {
+    Diag(CondExpr->getExprLoc(), diag::err_attribute_argument_type)
+        << ("'" + AttributeName.str() + "'") << AANT_ArgumentIntegerConstant
+        << CondExpr->getSourceRange();
+    return std::nullopt;
+  };
+
+  if (CondExpr->isTypeDependent() || CondExpr->isValueDependent()) {
+    if (CondExpr->containsUnexpandedParameterPack())
+      return BadExpr();
+    return FunctionEffectMode::Dependent;
+  }
+
+  std::optional<llvm::APSInt> ConditionValue =
+      CondExpr->getIntegerConstantExpr(Context);
+  if (!ConditionValue)
+    return BadExpr();
+  return ConditionValue->getExtValue() ? FunctionEffectMode::True
+                                       : FunctionEffectMode::False;
+}
+
+static bool
+handleNonBlockingNonAllocatingTypeAttr(TypeProcessingState &TPState,
+                                       ParsedAttr &PAttr, QualType &QT,
+                                       FunctionTypeUnwrapper &Unwrapped) {
+  // Delay if this is not a function type.
+  if (!Unwrapped.isFunctionType())
+    return false;
+
+  Sema &S = TPState.getSema();
+
+  // Require FunctionProtoType
+  auto *FPT = Unwrapped.get()->getAs<FunctionProtoType>();
+  if (FPT == nullptr) {
+    S.Diag(PAttr.getLoc(), diag::err_func_with_effects_no_prototype)
+        << PAttr.getAttrName()->getName();
+    return true;
+  }
+
+  // Parse the new  attribute.
+  // non/blocking or non/allocating? Or conditional (computed)?
+  const bool IsNonBlocking = PAttr.getKind() == ParsedAttr::AT_NonBlocking ||
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dougsonos wrote:

Not sure I understand the motivation to avoid `const` local variables - to me it reduces complexity for the reader.

https://github.com/llvm/llvm-project/pull/84983