[clang][Interp] Only diagnose null field access in constant contexts (#69223)

Looks like this should work as long as we don't dereference the value.

Author: tbaederr

clang/lib/AST/Interp/Interp.cpp

@@ -216,7 +216,7 @@ bool CheckLive(InterpState &S, CodePtr OpPC, const Pointer &Ptr,
 }
 
 bool CheckDummy(InterpState &S, CodePtr OpPC, const Pointer &Ptr) {
-  return !Ptr.isDummy();
+  return !Ptr.isZero() && !Ptr.isDummy();
 }
 
 bool CheckNull(InterpState &S, CodePtr OpPC, const Pointer &Ptr,

clang/lib/AST/Interp/Interp.h

@@ -1155,7 +1155,7 @@ inline bool GetPtrGlobal(InterpState &S, CodePtr OpPC, uint32_t I) {
 /// 2) Pushes Pointer.atField(Off) on the stack
 inline bool GetPtrField(InterpState &S, CodePtr OpPC, uint32_t Off) {
   const Pointer &Ptr = S.Stk.pop<Pointer>();
-  if (!CheckNull(S, OpPC, Ptr, CSK_Field))
+  if (S.inConstantContext() && !CheckNull(S, OpPC, Ptr, CSK_Field))
     return false;
   if (!CheckExtern(S, OpPC, Ptr))
     return false;

clang/lib/AST/Interp/Pointer.h

@@ -199,7 +199,10 @@ class Pointer {
   bool isField() const { return Base != 0 && Base != RootPtrMark; }
 
   /// Accessor for information about the declaration site.
-  const Descriptor *getDeclDesc() const { return Pointee->Desc; }
+  const Descriptor *getDeclDesc() const {
+    assert(Pointee);
+    return Pointee->Desc;
+  }
   SourceLocation getDeclLoc() const { return getDeclDesc()->getLocation(); }
 
   /// Returns a pointer to the object of which this pointer is a field.
@@ -296,11 +299,17 @@ class Pointer {
   bool isUnion() const;
 
   /// Checks if the storage is extern.
-  bool isExtern() const { return Pointee->isExtern(); }
+  bool isExtern() const { return Pointee && Pointee->isExtern(); }
   /// Checks if the storage is static.
-  bool isStatic() const { return Pointee->isStatic(); }
+  bool isStatic() const {
+    assert(Pointee);
+    return Pointee->isStatic();
+  }
   /// Checks if the storage is temporary.
-  bool isTemporary() const { return Pointee->isTemporary(); }
+  bool isTemporary() const {
+    assert(Pointee);
+    return Pointee->isTemporary();
+  }
   /// Checks if the storage is a static temporary.
   bool isStaticTemporary() const { return isStatic() && isTemporary(); }
 
@@ -323,7 +332,10 @@ class Pointer {
   }
 
   /// Returns the declaration ID.
-  std::optional<unsigned> getDeclID() const { return Pointee->getDeclID(); }
+  std::optional<unsigned> getDeclID() const {
+    assert(Pointee);
+    return Pointee->getDeclID();
+  }
 
   /// Returns the byte offset from the start.
   unsigned getByteOffset() const {
@@ -351,6 +363,8 @@ class Pointer {
 
   /// Checks if the index is one past end.
   bool isOnePastEnd() const {
+    if (!Pointee)
+      return false;
     return isElementPastEnd() || getSize() == getOffset();
   }
 
@@ -360,6 +374,7 @@ class Pointer {
   /// Dereferences the pointer, if it's live.
   template <typename T> T &deref() const {
     assert(isLive() && "Invalid pointer");
+    assert(Pointee);
     if (isArrayRoot())
       return *reinterpret_cast<T *>(Pointee->rawData() + Base +
                                     sizeof(InitMapPtr));
@@ -370,6 +385,7 @@ class Pointer {
   /// Dereferences a primitive element.
   template <typename T> T &elem(unsigned I) const {
     assert(I < getNumElems());
+    assert(Pointee);
     return reinterpret_cast<T *>(Pointee->data() + sizeof(InitMapPtr))[I];
   }
 
@@ -431,12 +447,14 @@ class Pointer {
   /// Returns a descriptor at a given offset.
   InlineDescriptor *getDescriptor(unsigned Offset) const {
     assert(Offset != 0 && "Not a nested pointer");
+    assert(Pointee);
     return reinterpret_cast<InlineDescriptor *>(Pointee->rawData() + Offset) -
            1;
   }
 
   /// Returns a reference to the InitMapPtr which stores the initialization map.
   InitMapPtr &getInitMap() const {
+    assert(Pointee);
     return *reinterpret_cast<InitMapPtr *>(Pointee->rawData() + Base);
   }
 

clang/test/AST/Interp/c.c

@@ -3,6 +3,8 @@
 // RUN: %clang_cc1 -verify=ref -std=c11 %s
 // RUN: %clang_cc1 -pedantic -verify=pedantic-ref -std=c11 %s
 
+typedef __INTPTR_TYPE__ intptr_t;
+
 _Static_assert(1, "");
 _Static_assert(0 != 1, "");
 _Static_assert(1.0 == 1.0, ""); // pedantic-ref-warning {{not an integer constant expression}} \
@@ -67,3 +69,15 @@ _Static_assert(&Test50 != (void*)0, ""); // ref-warning {{always true}} \
                                          // expected-warning {{always true}} \
                                          // pedantic-expected-warning {{always true}} \
                                          // pedantic-expected-warning {{is a GNU extension}}
+
+struct y {int x,y;};
+int a2[(intptr_t)&((struct y*)0)->y]; // expected-warning {{folded to constant array}} \
+                                      // pedantic-expected-warning {{folded to constant array}} \
+                                      // ref-warning {{folded to constant array}} \
+                                      // pedantic-ref-warning {{folded to constant array}}
+
+const struct y *yy = (struct y*)0;
+const intptr_t L = (intptr_t)(&(yy->y)); // expected-error {{not a compile-time constant}} \
+                                         // pedantic-expected-error {{not a compile-time constant}} \
+                                         // ref-error {{not a compile-time constant}} \
+                                         // pedantic-ref-error {{not a compile-time constant}}

clang/test/AST/Interp/records.cpp

@@ -1102,3 +1102,36 @@ namespace DelegatingConstructors {
   static_assert(d4.a == 10, "");
   static_assert(d4.b == 12, "");
 }
+
+namespace AccessOnNullptr {
+  struct F {
+    int a;
+  };
+
+  constexpr int a() { // expected-error {{never produces a constant expression}} \
+                      // ref-error {{never produces a constant expression}}
+    F *f = nullptr;
+
+    f->a = 0; // expected-note 2{{cannot access field of null pointer}} \
+              // ref-note 2{{cannot access field of null pointer}}
+    return f->a;
+  }
+  static_assert(a() == 0, ""); // expected-error {{not an integral constant expression}} \
+                               // expected-note {{in call to 'a()'}} \
+                               // ref-error {{not an integral constant expression}} \
+                               // ref-note {{in call to 'a()'}}
+
+  constexpr int a2() { // expected-error {{never produces a constant expression}} \
+                      // ref-error {{never produces a constant expression}}
+    F *f = nullptr;
+
+
+    const int *a = &(f->a); // expected-note 2{{cannot access field of null pointer}} \
+                            // ref-note 2{{cannot access field of null pointer}}
+    return f->a;
+  }
+  static_assert(a2() == 0, ""); // expected-error {{not an integral constant expression}} \
+                               // expected-note {{in call to 'a2()'}} \
+                               // ref-error {{not an integral constant expression}} \
+                               // ref-note {{in call to 'a2()'}}
+}