[clang][Interp] Implement add and sub compound assign operators

[aaron.ballman]

clang/test/AST/Interp/literals.cpp

415

I'd also like some test cases where the result of the operation is discarded. e.g.,

constexpr int func() {
  int i = 12;
  i += 10;
  return i;
}
static_assert(func() == 22);

and a test with a float-point type (okay for it to fail for the moment):

constexpr float func() {
  float f = 1.0f;
  f += 10.0f;
  return f;
}
static_assert(func() == 11.0f);

429

We also need tests for failure situations:

constexpr int func() {
  int i = __INT_MAX__;
  i += 1; // oops
  return i;
}

constexpr int another() {
  int i = __INT_MIN__;
  i -= 1; // oops
  return i;
}

[tbaeder]

clang/test/AST/Interp/literals.cpp

429

woops, I was sure I added this but it was for the ++/-- patch it seems.

[aaron.ballman]

LGTM!

clang/lib/AST/Interp/ByteCodeExprGen.h

public:
   bool VisitConstantExpr(const ConstantExpr *E);
   bool VisitUnaryExprOrTypeTraitExpr(const UnaryExprOrTypeTraitExpr *E);
   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);
 
 protected:
   bool visitExpr(const Expr *E) override;
   bool visitDecl(const VarDecl *VD) override;
 
 protected:
   /// Emits scope cleanup instructions.
   void emitCleanup();

clang/lib/AST/Interp/ByteCodeExprGen.cpp

 }
 
 template <class Emitter>
 bool ByteCodeExprGen<Emitter>::VisitCharacterLiteral(
     const CharacterLiteral *E) {
   return this->emitConst(E, E->getValue());
 }
 
+template <class Emitter>
+bool ByteCodeExprGen<Emitter>::VisitCompoundAssignOperator(
+    const CompoundAssignOperator *E) {
+  const Expr *LHS = E->getLHS();
+  const Expr *RHS = E->getRHS();
+  Optional<PrimType> LT = classify(E->getLHS()->getType());
+  Optional<PrimType> RT = classify(E->getRHS()->getType());
+
+  if (!LT || !RT)
+    return false;
+
+  assert(!E->getType()->isPointerType() &&
+         "Support pointer arithmethic in compound assignment operators");
+
+  // Get LHS pointer, load its value and get RHS value.
+  if (!visit(LHS))
+    return false;
+  if (!this->emitLoad(*LT, E))
+    return false;
+  if (!visit(RHS))
+    return false;
+
+  // Perform operation.
+  switch (E->getOpcode()) {
+  case BO_AddAssign:
+    if (!this->emitAdd(*LT, E))
+      return false;
+    break;
+  case BO_SubAssign:
+    if (!this->emitSub(*LT, E))
+      return false;
+    break;
+
+  case BO_MulAssign:
+  case BO_DivAssign:
+  case BO_RemAssign:
+  case BO_ShlAssign:
+  case BO_ShrAssign:
+  case BO_AndAssign:
+  case BO_XorAssign:
+  case BO_OrAssign:
+  default:
+    llvm_unreachable("Unimplemented compound assign operator");
+  }
+
+  // And store the result in LHS.
+  if (DiscardResult)
+    return this->emitStorePop(*LT, E);
+  return this->emitStore(*LT, E);
+}
+
 template <class Emitter> bool ByteCodeExprGen<Emitter>::discard(const Expr *E) {
   OptionScope<Emitter> Scope(this, /*NewDiscardResult=*/true);
   return this->Visit(E);
 }
 
 template <class Emitter>
 bool ByteCodeExprGen<Emitter>::visit(const Expr *E) {
   OptionScope<Emitter> Scope(this, /*NewDiscardResult=*/false);

clang/test/AST/Interp/literals.cpp

namespace IncDec {
 
   constexpr int UnderFlow() { // ref-error {{never produces a constant expression}}
     int a = INT_MIN;
     --a; // ref-note 2{{is outside the range}} \
          // expected-note {{is outside the range}}
     return -1;
   }
   static_assert(UnderFlow() == -1, "");  // expected-error {{not an integral constant expression}} \
                                          // expected-note {{in call to 'UnderFlow()'}} \
                                          // ref-error {{not an integral constant expression}} \
                                          // ref-note {{in call to 'UnderFlow()'}}
+
+  constexpr int getTwo() {
+    int i = 1;
+    return (i += 1);
+  }
+  static_assert(getTwo() == 2, "");
+
+  constexpr int sub(int a) {
+    return (a -= 2);
+  }
+  static_assert(sub(7) == 5, "");
+
+  constexpr int add(int a, int b) {
+    a += b; // expected-note {{is outside the range of representable values}} \
+            // ref-note {{is outside the range of representable values}} 
+    return a;
+  }
+  static_assert(add(1, 2) == 3, "");
+  static_assert(add(INT_MAX, 1) == 0, ""); // expected-error {{not an integral constant expression}} \
+                                           // expected-note {{in call to 'add}} \
+                                           // ref-error {{not an integral constant expression}} \
+                                           // ref-note {{in call to 'add}}
+
+  constexpr int sub(int a, int b) {
+    a -= b; // expected-note {{is outside the range of representable values}} \
+            // ref-note {{is outside the range of representable values}} 
+    return a;
+  }
+  static_assert(sub(10, 20) == -10, "");
+  static_assert(sub(INT_MIN, 1) == 0, ""); // expected-error {{not an integral constant expression}} \
+                                           // expected-note {{in call to 'sub}} \
+                                           // ref-error {{not an integral constant expression}} \
+                                           // ref-note {{in call to 'sub}}
+
+  constexpr int subAll(int a) {
+    return (a -= a);
+  }
+  static_assert(subAll(213) == 0, "");
 };
 #endif