Report error when a musttail call is made to a function marked with the not_tail_called attribute

Author: MillePlateaux

clang/docs/ReleaseNotes.rst

@@ -325,6 +325,9 @@ Improvements to Clang's diagnostics
 - Now correctly diagnose a tentative definition of an array with static
   storage duration in pedantic mode in C. (#GH50661)
 
+- The ``-err-musttail-mismatch`` error is emitted when a musttail call is made to a function marked with the not_tail_called attribute.(#133509).
+
+
 Improvements to Clang's time-trace
 ----------------------------------
 

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -3134,9 +3134,7 @@ def warn_function_attribute_ignored_in_stmt : Warning<
   "use '%0' on statements">,
   InGroup<IgnoredAttributes>;
 
-def err_musttail_conflicts_with_not_tail_called : Error<
-  "%0 musttail conflicts with not tail called"
-  >;
+
 def err_musttail_needs_trivial_args : Error<
   "tail call requires that the return value, all parameters, and any "
   "temporaries created by the expression are trivially destructible">;

clang/lib/Sema/SemaStmt.cpp

@@ -717,12 +717,11 @@ bool Sema::checkMustTailAttr(const Stmt *St, const Attr &MTA) {
     return false;
   }
 
-  if (const FunctionDecl *CalleeDecl = CE->getDirectCallee()) {
-    if (CalleeDecl->hasAttr<NotTailCalledAttr>()) {
-      Diag(St->getBeginLoc(), diag::err_musttail_conflicts_with_not_tail_called)
-          << &MTA;
-      return false;
-    }
+  if (const FunctionDecl *CalleeDecl = CE->getDirectCallee();
+     CalleeDecl && CalleeDecl->hasAttr<NotTailCalledAttr>()) {
+      Diag(St->getBeginLoc(), diag::err_musttail_mismatch)
+      << &MTA;
+     return false;
   }
 
   if (const auto *EWC = dyn_cast<ExprWithCleanups>(E)) {

clang/test/Sema/attr-musttail.cpp

@@ -0,0 +1,16 @@
+// RUN: %clang_cc1 -verify -fsyntax-only %s
+
+int __attribute__((not_tail_called)) foo1(int a) {
+    return a + 1;  
+}
+
+
+int foo2(int a) {
+    [[clang::musttail]] 
+    return foo1(a);  // expected-error{{cannot perform a tail call to function'musttail' because its signature is incompatible with the calling function}}
+}
+
+int main() {
+    int result = foo2(10);      
+    return 0;
+}