[clang][Interp] Diagnose reads from non-const global variables (#71919)

This fixes a long-standing FIXME item. Unfortunately it changes the diagnostic output of the tests added in `cxx23.cpp`, but they were wrong before and are wrong after, so no big deal.
llvm · Jan 13, 2024 · fc2766c · fc2766c
1 parent 33aaad9
commit fc2766c
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Showing 7 changed files with 126 additions and 20 deletions.
diff --git a/clang/lib/AST/Interp/ByteCodeExprGen.cpp b/clang/lib/AST/Interp/ByteCodeExprGen.cpp
@@ -2337,7 +2337,7 @@ bool ByteCodeExprGen<Emitter>::visitDecl(const VarDecl *VD) {
     auto GlobalIndex = P.getGlobal(VD);
     assert(GlobalIndex); // visitVarDecl() didn't return false.
     if (VarT) {
-      if (!this->emitGetGlobal(*VarT, *GlobalIndex, VD))
+      if (!this->emitGetGlobalUnchecked(*VarT, *GlobalIndex, VD))
         return false;
     } else {
       if (!this->emitGetPtrGlobal(*GlobalIndex, VD))

diff --git a/clang/lib/AST/Interp/Interp.cpp b/clang/lib/AST/Interp/Interp.cpp
@@ -53,6 +53,21 @@ static bool Jf(InterpState &S, CodePtr &PC, int32_t Offset) {
   return true;
 }
 
+static void diagnoseNonConstVariable(InterpState &S, CodePtr OpPC,
+                                     const ValueDecl *VD) {
+  if (!S.getLangOpts().CPlusPlus)
+    return;
+
+  const SourceInfo &Loc = S.Current->getSource(OpPC);
+  S.FFDiag(Loc,
+           VD->getType()->isIntegralOrEnumerationType()
+               ? diag::note_constexpr_ltor_non_const_int
+               : diag::note_constexpr_ltor_non_constexpr,
+           1)
+      << VD;
+  S.Note(VD->getLocation(), diag::note_declared_at);
+}
+
 static bool CheckActive(InterpState &S, CodePtr OpPC, const Pointer &Ptr,
                         AccessKinds AK) {
   if (Ptr.isActive())
@@ -171,9 +186,7 @@ bool CheckExtern(InterpState &S, CodePtr OpPC, const Pointer &Ptr) {
 
   if (!S.checkingPotentialConstantExpression() && S.getLangOpts().CPlusPlus) {
     const auto *VD = Ptr.getDeclDesc()->asValueDecl();
-    const SourceInfo &Loc = S.Current->getSource(OpPC);
-    S.FFDiag(Loc, diag::note_constexpr_ltor_non_constexpr, 1) << VD;
-    S.Note(VD->getLocation(), diag::note_declared_at);
+    diagnoseNonConstVariable(S, OpPC, VD);
   }
   return false;
 }
@@ -216,6 +229,24 @@ bool CheckLive(InterpState &S, CodePtr OpPC, const Pointer &Ptr,
   return true;
 }
 
+bool CheckConstant(InterpState &S, CodePtr OpPC, const Descriptor *Desc) {
+  assert(Desc);
+  if (const auto *D = Desc->asValueDecl()) {
+    if (const auto *VD = dyn_cast<VarDecl>(D);
+        VD && VD->hasGlobalStorage() &&
+        !(VD->isConstexpr() || VD->getType().isConstQualified())) {
+      diagnoseNonConstVariable(S, OpPC, VD);
+      return false;
+    }
+  }
+
+  return true;
+}
+
+static bool CheckConstant(InterpState &S, CodePtr OpPC, const Pointer &Ptr) {
+  return CheckConstant(S, OpPC, Ptr.getDeclDesc());
+}
+
 bool CheckDummy(InterpState &S, CodePtr OpPC, const Pointer &Ptr) {
   return !Ptr.isZero() && !Ptr.isDummy();
 }
@@ -304,6 +335,9 @@ bool CheckInitialized(InterpState &S, CodePtr OpPC, const Pointer &Ptr,
 bool CheckLoad(InterpState &S, CodePtr OpPC, const Pointer &Ptr) {
   if (!CheckLive(S, OpPC, Ptr, AK_Read))
     return false;
+  if (!CheckConstant(S, OpPC, Ptr))
+    return false;
+
   if (!CheckDummy(S, OpPC, Ptr))
     return false;
   if (!CheckExtern(S, OpPC, Ptr))
@@ -605,13 +639,7 @@ bool CheckDeclRef(InterpState &S, CodePtr OpPC, const DeclRefExpr *DR) {
     }
   } else if (const auto *VD = dyn_cast<VarDecl>(D)) {
     if (!VD->getType().isConstQualified()) {
-      S.FFDiag(E,
-               VD->getType()->isIntegralOrEnumerationType()
-                   ? diag::note_constexpr_ltor_non_const_int
-                   : diag::note_constexpr_ltor_non_constexpr,
-               1)
-          << VD;
-      S.Note(VD->getLocation(), diag::note_declared_at) << VD->getSourceRange();
+      diagnoseNonConstVariable(S, OpPC, VD);
       return false;
     }
 

diff --git a/clang/lib/AST/Interp/Interp.h b/clang/lib/AST/Interp/Interp.h
@@ -77,6 +77,9 @@ bool CheckSubobject(InterpState &S, CodePtr OpPC, const Pointer &Ptr,
 /// Checks if a pointer points to const storage.
 bool CheckConst(InterpState &S, CodePtr OpPC, const Pointer &Ptr);
 
+/// Checks if the Descriptor is of a constexpr or const global variable.
+bool CheckConstant(InterpState &S, CodePtr OpPC, const Descriptor *Desc);
+
 /// Checks if a pointer points to a mutable field.
 bool CheckMutable(InterpState &S, CodePtr OpPC, const Pointer &Ptr);
 
@@ -1004,12 +1007,23 @@ bool SetThisField(InterpState &S, CodePtr OpPC, uint32_t I) {
 template <PrimType Name, class T = typename PrimConv<Name>::T>
 bool GetGlobal(InterpState &S, CodePtr OpPC, uint32_t I) {
   const Block *B = S.P.getGlobal(I);
+
+  if (!CheckConstant(S, OpPC, B->getDescriptor()))
+    return false;
   if (B->isExtern())
     return false;
   S.Stk.push<T>(B->deref<T>());
   return true;
 }
 
+/// Same as GetGlobal, but without the checks.
+template <PrimType Name, class T = typename PrimConv<Name>::T>
+bool GetGlobalUnchecked(InterpState &S, CodePtr OpPC, uint32_t I) {
+  auto *B = S.P.getGlobal(I);
+  S.Stk.push<T>(B->deref<T>());
+  return true;
+}
+
 template <PrimType Name, class T = typename PrimConv<Name>::T>
 bool SetGlobal(InterpState &S, CodePtr OpPC, uint32_t I) {
   // TODO: emit warning.

diff --git a/clang/lib/AST/Interp/Opcodes.td b/clang/lib/AST/Interp/Opcodes.td
@@ -379,6 +379,7 @@ def CheckGlobalCtor : Opcode {}
 
 // [] -> [Value]
 def GetGlobal : AccessOpcode;
+def GetGlobalUnchecked : AccessOpcode;
 // [Value] -> []
 def InitGlobal : AccessOpcode;
 // [Value] -> []

diff --git a/clang/test/AST/Interp/arrays.cpp b/clang/test/AST/Interp/arrays.cpp
@@ -566,3 +566,35 @@ namespace GH69115 {
   static_assert(foo2() == 0, "");
 #endif
 }
+
+namespace NonConstReads {
+#if __cplusplus >= 202002L
+  void *p = nullptr; // ref-note {{declared here}} \
+                     // expected-note {{declared here}}
+
+  int arr[!p]; // ref-error {{not allowed at file scope}} \
+               // expected-error {{not allowed at file scope}} \
+               // ref-warning {{variable length arrays}} \
+               // ref-note {{read of non-constexpr variable 'p'}} \
+               // expected-warning {{variable length arrays}} \
+               // expected-note {{read of non-constexpr variable 'p'}}
+  int z; // ref-note {{declared here}} \
+         // expected-note {{declared here}}
+  int a[z]; // ref-error {{not allowed at file scope}} \
+            // expected-error {{not allowed at file scope}} \
+            // ref-warning {{variable length arrays}} \
+            // ref-note {{read of non-const variable 'z'}} \
+            // expected-warning {{variable length arrays}} \
+            // expected-note {{read of non-const variable 'z'}}
+#else
+  void *p = nullptr;
+  int arr[!p]; // ref-error {{not allowed at file scope}} \
+               // expected-error {{not allowed at file scope}}
+  int z;
+  int a[z]; // ref-error {{not allowed at file scope}} \
+            // expected-error {{not allowed at file scope}}
+#endif
+
+  const int y = 0;
+  int yy[y];
+}
diff --git a/clang/test/AST/Interp/cxx23.cpp b/clang/test/AST/Interp/cxx23.cpp
@@ -25,22 +25,32 @@ constexpr int g(int n) {        // ref20-error {{constexpr function never produc
 }
 
 constexpr int c_thread_local(int n) { // ref20-error {{constexpr function never produces a constant expression}} \
-                                      // ref23-error {{constexpr function never produces a constant expression}}
+                                      // ref23-error {{constexpr function never produces a constant expression}} \
+                                      // expected20-error {{constexpr function never produces a constant expression}} \
+                                      // expected23-error {{constexpr function never produces a constant expression}}
   static _Thread_local int m = 0;     // ref20-note {{control flows through the definition of a thread_local variable}} \
                                       // ref20-warning {{is a C++23 extension}} \
                                       // ref23-note {{control flows through the definition of a thread_local variable}} \
-                                      // expected20-warning {{is a C++23 extension}}
-  return m;
+                                      // expected20-warning {{is a C++23 extension}} \
+                                      // expected20-note {{declared here}} \
+                                      // expected23-note {{declared here}}
+  return m; // expected20-note {{read of non-const variable}} \
+            // expected23-note {{read of non-const variable}}
 }
 
 
 constexpr int gnu_thread_local(int n) { // ref20-error {{constexpr function never produces a constant expression}} \
-                                        // ref23-error {{constexpr function never produces a constant expression}}
+                                        // ref23-error {{constexpr function never produces a constant expression}} \
+                                        // expected20-error {{constexpr function never produces a constant expression}} \
+                                        // expected23-error {{constexpr function never produces a constant expression}}
   static __thread int m = 0;            // ref20-note {{control flows through the definition of a thread_local variable}} \
                                         // ref20-warning {{is a C++23 extension}} \
                                         // ref23-note {{control flows through the definition of a thread_local variable}} \
-                                        // expected20-warning {{is a C++23 extension}}
-  return m;
+                                        // expected20-warning {{is a C++23 extension}} \
+                                        // expected20-note {{declared here}} \
+                                        // expected23-note {{declared here}}
+  return m; // expected20-note {{read of non-const variable}} \
+            // expected23-note {{read of non-const variable}}
 }
 
 constexpr int h(int n) {  // ref20-error {{constexpr function never produces a constant expression}} \

diff --git a/clang/test/AST/Interp/literals.cpp b/clang/test/AST/Interp/literals.cpp
@@ -1181,8 +1181,29 @@ namespace InvalidDeclRefs {
                           // expected-error {{not an integral constant expression}} \
                           // expected-note {{initializer of 'b02' is unknown}}
 
-  /// FIXME: This should also be diagnosed in the new interpreter.
-  int b03 = 3; // ref-note {{declared here}}
+  int b03 = 3; // ref-note {{declared here}} \
+               // expected-note {{declared here}}
   static_assert(b03, ""); // ref-error {{not an integral constant expression}} \
-                          // ref-note {{read of non-const variable}}
+                          // ref-note {{read of non-const variable}} \
+                          // expected-error {{not an integral constant expression}} \
+                          // expected-note {{read of non-const variable}}
+}
+
+namespace NonConstReads {
+  void *p = nullptr; // ref-note {{declared here}} \
+                     // expected-note {{declared here}}
+  static_assert(!p, ""); // ref-error {{not an integral constant expression}} \
+                         // ref-note {{read of non-constexpr variable 'p'}} \
+                         // expected-error {{not an integral constant expression}} \
+                         // expected-note {{read of non-constexpr variable 'p'}}
+
+  int arr[!p]; // ref-error {{variable length array}} \
+               // expected-error {{variable length array}}
+
+  int z; // ref-note {{declared here}} \
+         // expected-note {{declared here}}
+  static_assert(z == 0, ""); // ref-error {{not an integral constant expression}} \
+                             // ref-note {{read of non-const variable 'z'}} \
+                             // expected-error {{not an integral constant expression}} \
+                             // expected-note {{read of non-const variable 'z'}}
 }