[clang][bytecode] Diagnose dereferencing a null pointer (llvm#149330)

Author: tbaederr

clang/lib/AST/ByteCode/Compiler.cpp

@@ -6375,6 +6375,9 @@ bool Compiler<Emitter>::VisitUnaryOperator(const UnaryOperator *E) {
     if (!this->visit(SubExpr))
       return false;
 
+    if (!this->emitCheckNull(E))
+      return false;
+
     if (classifyPrim(SubExpr) == PT_Ptr)
       return this->emitNarrowPtr(E);
     return true;

clang/lib/AST/ByteCode/Interp.h

@@ -1885,6 +1885,16 @@ inline bool Dump(InterpState &S, CodePtr OpPC) {
   return true;
 }
 
+inline bool CheckNull(InterpState &S, CodePtr OpPC) {
+  const auto &Ptr = S.Stk.peek<Pointer>();
+  if (Ptr.isZero()) {
+    S.FFDiag(S.Current->getSource(OpPC),
+             diag::note_constexpr_dereferencing_null);
+    return S.noteUndefinedBehavior();
+  }
+  return true;
+}
+
 inline bool VirtBaseHelper(InterpState &S, CodePtr OpPC, const RecordDecl *Decl,
                            const Pointer &Ptr) {
   Pointer Base = Ptr;

clang/lib/AST/ByteCode/Opcodes.td

@@ -865,6 +865,7 @@ def CheckNewTypeMismatchArray : Opcode {
 
 def IsConstantContext: Opcode;
 def CheckAllocations : Opcode;
+def CheckNull : Opcode;
 
 def BitCastTypeClass : TypeClass {
   let Types = [Uint8, Sint8, Uint16, Sint16, Uint32, Sint32, Uint64, Sint64,

clang/test/AST/ByteCode/complex.cpp

@@ -396,10 +396,9 @@ namespace ComplexConstexpr {
                                     // both-note {{cannot refer to element 3 of array of 2 elements}}
   constexpr _Complex float *p = 0;
   constexpr float pr = __real *p; // both-error {{constant expr}} \
-                                  // expected-note {{read of dereferenced null pointer}} \
-                                  // ref-note {{dereferencing a null pointer}}
+                                  // both-note {{dereferencing a null pointer}}
   constexpr float pi = __imag *p; // both-error {{constant expr}} \
-                                  // ref-note {{dereferencing a null pointer}}
+                                  // both-note {{dereferencing a null pointer}}
   constexpr const _Complex double *q = &test3 + 1;
   constexpr double qr = __real *q; // ref-error {{constant expr}} \
                                    // ref-note {{cannot access real component of pointer past the end}}

clang/test/AST/ByteCode/const-eval.c

@@ -180,6 +180,9 @@ typedef __INTPTR_TYPE__ intptr_t;
 const intptr_t A = (intptr_t)(((int*) 0) + 1);
 const intptr_t B = (intptr_t)(((char*)0) + 3);
 _Static_assert(A > B, "");
+int * GH149500_p = &(*(int *)0x400);
+static const void *GH149500_q = &(*(const struct sysrq_key_op *)0);
+
 #else
 #error :(
 #endif

clang/test/AST/ByteCode/cxx11.cpp

@@ -39,9 +39,8 @@ struct S {
 constexpr S s = { 5 };
 constexpr const int *p = &s.m + 1;
 
-constexpr const int *np2 = &(*(int(*)[4])nullptr)[0];
-// ref-error@-1 {{constexpr variable 'np2' must be initialized by a constant expression}} \
-// ref-note@-1  {{dereferencing a null pointer is not allowed in a constant expression}}
+constexpr const int *np2 = &(*(int(*)[4])nullptr)[0]; // both-error {{constexpr variable 'np2' must be initialized by a constant expression}} \
+                                                      // both-note  {{dereferencing a null pointer is not allowed in a constant expression}}
 
 constexpr int preDec(int x) { // both-error {{never produces a constant expression}}
   return --x;                 // both-note {{subexpression}}

clang/test/AST/ByteCode/records.cpp

@@ -1660,11 +1660,9 @@ namespace NullptrCast {
   constexpr A *na = nullptr;
   constexpr B *nb = nullptr;
   constexpr A &ra = *nb; // both-error {{constant expression}} \
-                         // ref-note {{dereferencing a null pointer}} \
-                         // expected-note {{cannot access base class of null pointer}}
+                         // both-note {{dereferencing a null pointer}}
   constexpr B &rb = (B&)*na; // both-error {{constant expression}} \
-                             // ref-note {{dereferencing a null pointer}} \
-                             // expected-note {{cannot access derived class of null pointer}}
+                             // both-note {{dereferencing a null pointer}}
   constexpr bool test() {
     auto a = (A*)(B*)nullptr;
 

clang/test/CXX/drs/cwg14xx.cpp

@@ -6,6 +6,14 @@
 // RUN: %clang_cc1 -std=c++23 %s -verify=expected,since-cxx11,since-cxx14,since-cxx20 -fexceptions -fcxx-exceptions -pedantic-errors
 // RUN: %clang_cc1 -std=c++2c %s -verify=expected,since-cxx11,since-cxx14,since-cxx20 -fexceptions -fcxx-exceptions -pedantic-errors
 
+// RUN: %clang_cc1 -std=c++98 %s -verify=expected -fexceptions -fcxx-exceptions -pedantic-errors -fexperimental-new-constant-interpreter
+// RUN: %clang_cc1 -std=c++11 %s -verify=expected,cxx11-17,since-cxx11, -fexceptions -fcxx-exceptions -pedantic-errors -fexperimental-new-constant-interpreter
+// RUN: %clang_cc1 -std=c++14 %s -verify=expected,cxx14-17,cxx11-17,since-cxx11,since-cxx14 -fexceptions -fcxx-exceptions -pedantic-errors -fexperimental-new-constant-interpreter
+// RUN: %clang_cc1 -std=c++17 %s -verify=expected,cxx14-17,cxx11-17,since-cxx11,since-cxx14 -fexceptions -fcxx-exceptions -pedantic-errors -fexperimental-new-constant-interpreter
+// RUN: %clang_cc1 -std=c++20 %s -verify=expected,since-cxx11,since-cxx14,since-cxx20 -fexceptions -fcxx-exceptions -pedantic-errors -fexperimental-new-constant-interpreter
+// RUN: %clang_cc1 -std=c++23 %s -verify=expected,since-cxx11,since-cxx14,since-cxx20 -fexceptions -fcxx-exceptions -pedantic-errors -fexperimental-new-constant-interpreter
+// RUN: %clang_cc1 -std=c++2c %s -verify=expected,since-cxx11,since-cxx14,since-cxx20 -fexceptions -fcxx-exceptions -pedantic-errors -fexperimental-new-constant-interpreter
+
 namespace cwg1413 { // cwg1413: 12
   template<int> struct Check {
     typedef int type;