[clang][Interp] Implement __builtin_offsetof

Differential Revision: https://reviews.llvm.org/D156400

clang/lib/AST/Interp/ByteCodeExprGen.cpp

@@ -1453,6 +1453,41 @@ bool ByteCodeExprGen<Emitter>::VisitSourceLocExpr(const SourceLocExpr *E) {
   return true;
 }
 
+template <class Emitter>
+bool ByteCodeExprGen<Emitter>::VisitOffsetOfExpr(const OffsetOfExpr *E) {
+  unsigned N = E->getNumComponents();
+  if (N == 0)
+    return false;
+
+  for (unsigned I = 0; I != N; ++I) {
+    const OffsetOfNode &Node = E->getComponent(I);
+    if (Node.getKind() == OffsetOfNode::Array) {
+      const Expr *ArrayIndexExpr = E->getIndexExpr(Node.getArrayExprIndex());
+      PrimType IndexT = classifyPrim(ArrayIndexExpr->getType());
+
+      if (DiscardResult) {
+        if (!this->discard(ArrayIndexExpr))
+          return false;
+        continue;
+      }
+
+      if (!this->visit(ArrayIndexExpr))
+        return false;
+      // Cast to Sint64.
+      if (IndexT != PT_Sint64) {
+        if (!this->emitCast(IndexT, PT_Sint64, E))
+          return false;
+      }
+    }
+  }
+
+  if (DiscardResult)
+    return true;
+
+  PrimType T = classifyPrim(E->getType());
+  return this->emitOffsetOf(T, E, E);
+}
+
 template <class Emitter> bool ByteCodeExprGen<Emitter>::discard(const Expr *E) {
   if (E->containsErrors())
     return false;

clang/lib/AST/Interp/ByteCodeExprGen.h

@@ -105,6 +105,7 @@ class ByteCodeExprGen : public ConstStmtVisitor<ByteCodeExprGen<Emitter>, bool>,
   bool VisitCXXNoexceptExpr(const CXXNoexceptExpr *E);
   bool VisitCXXConstructExpr(const CXXConstructExpr *E);
   bool VisitSourceLocExpr(const SourceLocExpr *E);
+  bool VisitOffsetOfExpr(const OffsetOfExpr *E);
 
 protected:
   bool visitExpr(const Expr *E) override;

clang/lib/AST/Interp/Interp.h

@@ -181,6 +181,10 @@ bool Interpret(InterpState &S, APValue &Result);
 bool InterpretBuiltin(InterpState &S, CodePtr OpPC, const Function *F,
                       const CallExpr *Call);
 
+/// Interpret an offsetof operation.
+bool InterpretOffsetOf(InterpState &S, CodePtr OpPC, const OffsetOfExpr *E,
+                       llvm::ArrayRef<int64_t> ArrayIndices, int64_t &Result);
+
 enum class ArithOp { Add, Sub };
 
 //===----------------------------------------------------------------------===//
@@ -1839,6 +1843,21 @@ inline bool InvalidCast(InterpState &S, CodePtr OpPC, CastKind Kind) {
   return false;
 }
 
+template <PrimType Name, class T = typename PrimConv<Name>::T>
+inline bool OffsetOf(InterpState &S, CodePtr OpPC, const OffsetOfExpr *E) {
+  llvm::SmallVector<int64_t> ArrayIndices;
+  for (size_t I = 0; I != E->getNumExpressions(); ++I)
+    ArrayIndices.emplace_back(S.Stk.pop<int64_t>());
+
+  int64_t Result;
+  if (!InterpretOffsetOf(S, OpPC, E, ArrayIndices, Result))
+    return false;
+
+  S.Stk.push<T>(T::from(Result));
+
+  return true;
+}
+
 //===----------------------------------------------------------------------===//
 // Read opcode arguments
 //===----------------------------------------------------------------------===//

clang/lib/AST/Interp/InterpBuiltin.cpp

@@ -8,6 +8,7 @@
 #include "Boolean.h"
 #include "Interp.h"
 #include "PrimType.h"
+#include "clang/AST/RecordLayout.h"
 #include "clang/Basic/Builtins.h"
 #include "clang/Basic/TargetInfo.h"
 
@@ -519,5 +520,79 @@ bool InterpretBuiltin(InterpState &S, CodePtr OpPC, const Function *F,
   return false;
 }
 
+bool InterpretOffsetOf(InterpState &S, CodePtr OpPC, const OffsetOfExpr *E,
+                       llvm::ArrayRef<int64_t> ArrayIndices,
+                       int64_t &IntResult) {
+  CharUnits Result;
+  unsigned N = E->getNumComponents();
+  assert(N > 0);
+
+  unsigned ArrayIndex = 0;
+  QualType CurrentType = E->getTypeSourceInfo()->getType();
+  for (unsigned I = 0; I != N; ++I) {
+    const OffsetOfNode &Node = E->getComponent(I);
+    switch (Node.getKind()) {
+    case OffsetOfNode::Field: {
+      const FieldDecl *MemberDecl = Node.getField();
+      const RecordType *RT = CurrentType->getAs<RecordType>();
+      if (!RT)
+        return false;
+      RecordDecl *RD = RT->getDecl();
+      if (RD->isInvalidDecl())
+        return false;
+      const ASTRecordLayout &RL = S.getCtx().getASTRecordLayout(RD);
+      unsigned FieldIndex = MemberDecl->getFieldIndex();
+      assert(FieldIndex < RL.getFieldCount() && "offsetof field in wrong type");
+      Result += S.getCtx().toCharUnitsFromBits(RL.getFieldOffset(FieldIndex));
+      CurrentType = MemberDecl->getType().getNonReferenceType();
+      break;
+    }
+    case OffsetOfNode::Array: {
+      // When generating bytecode, we put all the index expressions as Sint64 on
+      // the stack.
+      int64_t Index = ArrayIndices[ArrayIndex];
+      const ArrayType *AT = S.getCtx().getAsArrayType(CurrentType);
+      if (!AT)
+        return false;
+      CurrentType = AT->getElementType();
+      CharUnits ElementSize = S.getCtx().getTypeSizeInChars(CurrentType);
+      Result += Index * ElementSize;
+      ++ArrayIndex;
+      break;
+    }
+    case OffsetOfNode::Base: {
+      const CXXBaseSpecifier *BaseSpec = Node.getBase();
+      if (BaseSpec->isVirtual())
+        return false;
+
+      // Find the layout of the class whose base we are looking into.
+      const RecordType *RT = CurrentType->getAs<RecordType>();
+      if (!RT)
+        return false;
+      const RecordDecl *RD = RT->getDecl();
+      if (RD->isInvalidDecl())
+        return false;
+      const ASTRecordLayout &RL = S.getCtx().getASTRecordLayout(RD);
+
+      // Find the base class itself.
+      CurrentType = BaseSpec->getType();
+      const RecordType *BaseRT = CurrentType->getAs<RecordType>();
+      if (!BaseRT)
+        return false;
+
+      // Add the offset to the base.
+      Result += RL.getBaseClassOffset(cast<CXXRecordDecl>(BaseRT->getDecl()));
+      break;
+    }
+    case OffsetOfNode::Identifier:
+      llvm_unreachable("Dependent OffsetOfExpr?");
+    }
+  }
+
+  IntResult = Result.getQuantity();
+
+  return true;
+}
+
 } // namespace interp
 } // namespace clang

clang/lib/AST/Interp/Opcodes.td

@@ -53,6 +53,7 @@ def ArgRoundingMode : ArgType { let Name = "llvm::RoundingMode"; }
 def ArgLETD: ArgType { let Name = "const LifetimeExtendedTemporaryDecl *"; }
 def ArgCastKind : ArgType { let Name = "CastKind"; }
 def ArgCallExpr : ArgType { let Name = "const CallExpr *"; }
+def ArgOffsetOfExpr : ArgType { let Name = "const OffsetOfExpr *"; }
 
 //===----------------------------------------------------------------------===//
 // Classes of types instructions operate on.
@@ -198,6 +199,12 @@ def CallPtr : Opcode {
   let Types = [];
 }
 
+def OffsetOf : Opcode {
+  let Types = [IntegerTypeClass];
+  let Args = [ArgOffsetOfExpr];
+  let HasGroup = 1;
+}
+
 //===----------------------------------------------------------------------===//
 // Frame management
 //===----------------------------------------------------------------------===//