[clang][Interp] Support pointer types in compound assignment operations

[tbaeder]

Summary

This was still missing.

[erichkeane]

I'm pretty far behind on reviews of the interpreter, but this one I noticed while looking th rough it.

clang/lib/AST/Interp/ByteCodeExprGen.cpp

697

This is UB here if LT doesn't contain a value. Additionally, it makes line 712 really odd here. It seems that LT isn't really used anywhere in this function. I know classify is meaningful here (and thus needs to run), but I wonder if we want to make this:

assert(LT && *LT == PT_Ptr); and take out the 1st test on 712.

[aaron.ballman]

clang/lib/AST/Interp/ByteCodeExprGen.cpp

714–715

Should this be an early return before we visit anything? Or an assert on the assumption that we should only get here for += and -=?

[tbaeder]

clang/lib/AST/Interp/ByteCodeExprGen.cpp

714–715

Sure, that would work as well.

[tbaeder]

Ping

[aaron.ballman]

LGTM

clang/lib/AST/Interp/ByteCodeExprGen.h

public:
   bool VisitMemberExpr(const MemberExpr *E);
   bool VisitArrayInitIndexExpr(const ArrayInitIndexExpr *E);
   bool VisitOpaqueValueExpr(const OpaqueValueExpr *E);
   bool VisitAbstractConditionalOperator(const AbstractConditionalOperator *E);
   bool VisitStringLiteral(const StringLiteral *E);
   bool VisitCharacterLiteral(const CharacterLiteral *E);
   bool VisitCompoundAssignOperator(const CompoundAssignOperator *E);
   bool VisitFloatCompoundAssignOperator(const CompoundAssignOperator *E);
+  bool VisitPointerCompoundAssignOperator(const CompoundAssignOperator *E);
   bool VisitExprWithCleanups(const ExprWithCleanups *E);
   bool VisitMaterializeTemporaryExpr(const MaterializeTemporaryExpr *E);
 
 protected:
   bool visitExpr(const Expr *E) override;
   bool visitDecl(const VarDecl *VD) override;
 
 protected:

clang/lib/AST/Interp/ByteCodeExprGen.cpp

bool ByteCodeExprGen<Emitter>::VisitFloatCompoundAssignOperator(
   }
 
   if (DiscardResult)
     return this->emitStorePop(*LT, E);
   return this->emitStore(*LT, E);
 }
 
 template <class Emitter>
+bool ByteCodeExprGen<Emitter>::VisitPointerCompoundAssignOperator(
+    const CompoundAssignOperator *E) {
+  BinaryOperatorKind Op = E->getOpcode();
+  const Expr *LHS = E->getLHS();
+  const Expr *RHS = E->getRHS();
+  std::optional<PrimType> LT = classify(LHS->getType());
+  std::optional<PrimType> RT = classify(RHS->getType());
+
+  if (Op != BO_AddAssign && Op != BO_SubAssign)
+    return false;
+
+  if (!LT || !RT)
+    return false;
+  assert(*LT == PT_Ptr);
+
+  if (!visit(LHS))
+    return false;
+
+  if (!this->emitLoadPtr(LHS))
+    return false;
+
+  if (!visit(RHS))
+    return false;
+
+  if (Op == BO_AddAssign)
+    this->emitAddOffset(*RT, E);
+  else
+    this->emitSubOffset(*RT, E);
+
+  if (DiscardResult)
+    return this->emitStorePopPtr(E);
+  return this->emitStorePtr(E);
+}
+
+template <class Emitter>
 bool ByteCodeExprGen<Emitter>::VisitCompoundAssignOperator(
     const CompoundAssignOperator *E) {
 
   // Handle floating point operations separately here, since they
   // require special care.
   if (E->getType()->isFloatingType())
     return VisitFloatCompoundAssignOperator(E);
 
+  if (E->getType()->isPointerType())
+    return VisitPointerCompoundAssignOperator(E);
+
   const Expr *LHS = E->getLHS();
   const Expr *RHS = E->getRHS();
   std::optional<PrimType> LHSComputationT =
       classify(E->getComputationLHSType());
   std::optional<PrimType> LT = classify(LHS->getType());
   std::optional<PrimType> RT = classify(E->getComputationResultType());
   std::optional<PrimType> ResultT = classify(E->getType());
 
   if (!LT || !RT || !ResultT || !LHSComputationT)
     return false;
 
-  assert(!E->getType()->isPointerType() &&
-         "Support pointer arithmethic in compound assignment operators");
-
+  assert(!E->getType()->isPointerType() && "Handled above");
   assert(!E->getType()->isFloatingType() && "Handled above");
 
   // Get LHS pointer, load its value and get RHS value.
   if (!visit(LHS))
     return false;
   if (!this->emitLoad(*LT, E))
     return false;
   // If necessary, cast LHS to its computation type.

clang/test/AST/Interp/literals.cpp

namespace IncDec {
   static_assert(IntMul(2, 2) == 4, "");
   static_assert(IntMul(12, 20) == 240, "");
   static_assert(IntMul(2, 1) == 2, "");
   static_assert(IntMul(9, 7) == 63, "");
   static_assert(IntMul(INT_MAX, 2) == 0, ""); // expected-error {{not an integral constant expression}} \
                                               // expected-note {{in call to 'IntMul}} \
                                               // ref-error {{not an integral constant expression}} \
                                               // ref-note {{in call to 'IntMul}}
+  constexpr int arr[] = {1,2,3};
+  constexpr int ptrInc1() {
+    const int *p = arr;
+    p += 2;
+    return *p;
+  }
+  static_assert(ptrInc1() == 3, "");
+
+  constexpr int ptrInc2() {
+    const int *p = arr;
+    return *(p += 1);
+  }
+  static_assert(ptrInc2() == 2, "");
+
+  constexpr int ptrInc3() { // expected-error {{never produces a constant expression}} \
+                            // ref-error {{never produces a constant expression}}
+    const int *p = arr;
+    p += 12; // expected-note {{cannot refer to element 12 of array of 3 elements}} \
+             // ref-note {{cannot refer to element 12 of array of 3 elements}}
+    return *p;
+  }
+
+  constexpr int ptrIncDec1() {
+    const int *p = arr;
+    p += 2;
+    p -= 1;
+    return *p;
+  }
+  static_assert(ptrIncDec1() == 2, "");
+
+  constexpr int ptrDec1() { // expected-error {{never produces a constant expression}} \
+                        // ref-error {{never produces a constant expression}}
+    const int *p = arr;
+    p -= 1;  // expected-note {{cannot refer to element -1 of array of 3 elements}} \
+             // ref-note {{cannot refer to element -1 of array of 3 elements}}
+    return *p;
+  }
 };
 #endif