[Clang] FunctionEffects: properly extract the type of a bound member member function from a CallExpr. (llvm#166101)

There's a bug illustrated by this example:

```
template <typename T>
struct Holder {
	T value;
	
	T& operator*() { return value; }
};

struct X {
	using Dispatch = float (X::*)() [[clang::nonblocking]];
    
	void fails(Holder<Dispatch>& holder) [[clang::nonblocking]]
	{
		(this->*(*holder))();   <<< the expression is incorrectly determined not to be nonblocking
	}

	void succeeds(Holder<Dispatch>& holder) [[clang::nonblocking]]
	{
		auto func = *holder;
		(this->*func)();
	}
};
```

In both cases we have a `CXXMemberCallExpr`. In `succeeds`, the
expression refers to a `Decl` (`func`) and gets a useful PTMF type. In
`fails`, the expression does not refer to a `Decl` and its type is
special, printed as `bound member function`. `Expr` provides a method
for extracting the true type so we can use that in this situation.

---------

Co-authored-by: Doug Wyatt <[email protected]>
Co-authored-by: Sirraide <[email protected]>

Author: 3 people

clang/lib/Sema/SemaFunctionEffects.cpp

@@ -1208,8 +1208,16 @@ class Analyzer {
         return true;
       }
 
-      // No Decl, just an Expr. Just check based on its type.
-      checkIndirectCall(Call, CalleeExpr->getType());
+      // No Decl, just an Expr. Just check based on its type. Bound member
+      // functions are a special expression type and need to be specially
+      // unpacked.
+      QualType CalleeExprQT = CalleeExpr->getType();
+      if (CalleeExpr->isBoundMemberFunction(Outer.S.getASTContext())) {
+        QualType QT = Expr::findBoundMemberType(CalleeExpr);
+        if (!QT.isNull())
+          CalleeExprQT = QT;
+      }
+      checkIndirectCall(Call, CalleeExprQT);
 
       return true;
     }

clang/test/Sema/attr-nonblocking-constraints.cpp

@@ -235,16 +235,35 @@ void nb13() [[clang::nonblocking]] { nb12(); }
 // C++ member function pointers
 struct PTMFTester {
 	typedef void (PTMFTester::*ConvertFunction)() [[clang::nonblocking]];
-
-	void convert() [[clang::nonblocking]];
+	typedef void (PTMFTester::*BlockingFunction)();
 
 	ConvertFunction mConvertFunc;
-};
 
-void PTMFTester::convert() [[clang::nonblocking]]
-{
-	(this->*mConvertFunc)();
-}
+	void convert() [[clang::nonblocking]]
+	{
+		(this->*mConvertFunc)(); // This should not generate a warning.
+	}
+
+	template <typename T>
+	struct Holder {
+		T value;
+		
+		T& operator*() { return value; }
+	};
+
+
+	void ptmfInExpr(Holder<ConvertFunction>& holder) [[clang::nonblocking]]
+	{
+		(this->*(*holder))();   // Should not generate a warning.
+		((*this).*(*holder))(); // Should not generate a warning.
+	}
+
+	void ptmfInExpr(Holder<BlockingFunction>& holder) [[clang::nonblocking]]
+	{
+		(this->*(*holder))(); // expected-warning {{function with 'nonblocking' attribute must not call non-'nonblocking' expression}}
+		((*this).*(*holder))(); // expected-warning {{function with 'nonblocking' attribute must not call non-'nonblocking' expression}}
+	}
+};
 
 // Allow implicit conversion from array to pointer.
 void nb14(unsigned idx) [[clang::nonblocking]]