[clang][bytecode] Reject constexpr-unknown pointers from Inc ops (llvm#135548)

We used to accept c++ as a known value here, causing wrong codegen.

Author: tbaederr

clang/lib/AST/ByteCode/Interp.cpp

@@ -307,7 +307,7 @@ bool isConstexprUnknown(const Pointer &P) {
   if (P.isDummy())
     return false;
   const VarDecl *VD = P.block()->getDescriptor()->asVarDecl();
-  return VD && VD->hasLocalStorage();
+  return VD && VD->hasLocalStorage() && !isa<ParmVarDecl>(VD);
 }
 
 bool CheckBCPResult(InterpState &S, const Pointer &Ptr) {

clang/lib/AST/ByteCode/Interp.h

@@ -771,6 +771,11 @@ bool IncDecHelper(InterpState &S, CodePtr OpPC, const Pointer &Ptr,
                   bool CanOverflow) {
   assert(!Ptr.isDummy());
 
+  if (!S.inConstantContext()) {
+    if (isConstexprUnknown(Ptr))
+      return false;
+  }
+
   if constexpr (std::is_same_v<T, Boolean>) {
     if (!S.getLangOpts().CPlusPlus14)
       return Invalid(S, OpPC);

clang/test/AST/ByteCode/codegen.cpp

@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -triple x86_64-linux -emit-llvm -o - %s | FileCheck %s
+// RUN: %clang_cc1 -triple x86_64-linux -emit-llvm -o - %s                                         | FileCheck %s
 // RUN: %clang_cc1 -triple x86_64-linux -emit-llvm -o - %s -fexperimental-new-constant-interpreter | FileCheck %s
 
 #ifdef __SIZEOF_INT128__
@@ -95,3 +95,12 @@ void f(A *a) {
   // CHECK: call void @_ZN1AD1Ev(
   A::E e3 = A().Foo;
 }
+
+int notdead() {
+  auto l = [c=0]() mutable {
+    return  c++ < 5 ? 10 : 12;
+  };
+  return l();
+}
+// CHECK: _ZZ7notdeadvEN3$_0clEv
+// CHECK: ret i32 %cond