[clang][Interp] Fix function pointer callexpr eval order (#101821)

We need to evaluate the callee before the arguments.

Author: tbaederr

clang/lib/AST/Interp/Compiler.cpp

@@ -4003,6 +4003,13 @@ bool Compiler<Emitter>::VisitCallExpr(const CallExpr *E) {
     } else if (!this->visit(MC->getImplicitObjectArgument())) {
       return false;
     }
+  } else if (!FuncDecl) {
+    const Expr *Callee = E->getCallee();
+    CalleeOffset = this->allocateLocalPrimitive(Callee, PT_FnPtr, true, false);
+    if (!this->visit(Callee))
+      return false;
+    if (!this->emitSetLocal(PT_FnPtr, *CalleeOffset, E))
+      return false;
   }
 
   llvm::BitVector NonNullArgs = collectNonNullArgs(FuncDecl, Args);
@@ -4071,22 +4078,19 @@ bool Compiler<Emitter>::VisitCallExpr(const CallExpr *E) {
     for (unsigned I = 0, N = E->getNumArgs(); I != N; ++I)
       ArgSize += align(primSize(classify(E->getArg(I)).value_or(PT_Ptr)));
 
-    // Get the callee, either from a member pointer saved in CalleeOffset,
-    // or by just visiting the Callee expr.
-    if (CalleeOffset) {
+    // Get the callee, either from a member pointer or function pointer saved in
+    // CalleeOffset.
+    if (isa<CXXMemberCallExpr>(E) && CalleeOffset) {
       if (!this->emitGetLocal(PT_MemberPtr, *CalleeOffset, E))
         return false;
       if (!this->emitGetMemberPtrDecl(E))
         return false;
-      if (!this->emitCallPtr(ArgSize, E, E))
-        return false;
     } else {
-      if (!this->visit(E->getCallee()))
-        return false;
-
-      if (!this->emitCallPtr(ArgSize, E, E))
+      if (!this->emitGetLocal(PT_FnPtr, *CalleeOffset, E))
         return false;
     }
+    if (!this->emitCallPtr(ArgSize, E, E))
+      return false;
   }
 
   // Cleanup for discarded return values.

clang/test/AST/Interp/eval-order.cpp

@@ -45,7 +45,7 @@ namespace EvalOrder {
     }
     template <typename T> constexpr T &&b(T &&v) {
       if (!done_a)
-        throw "wrong"; // expected-note 5{{not valid}}
+        throw "wrong"; // expected-note 4{{not valid}}
       done_b = true;
       return (T &&)v;
     }
@@ -75,8 +75,7 @@ namespace EvalOrder {
   SEQ(A(&ud)->*B(&UserDefined::n));
 
   // Rule 4: a(b1, b2, b3)
-  SEQ(A(f)(B(1), B(2), B(3))); // expected-error {{not an integral constant expression}} FIXME \
-                               // expected-note 2{{in call to}}
+  SEQ(A(f)(B(1), B(2), B(3)));
 
   // Rule 5: b = a, b @= a
   SEQ(B(lvalue<int>().get()) = A(0)); // expected-error {{not an integral constant expression}} FIXME \