path: root/lib/CodeGen/CGExprConstant.cpp

//===--- CGExprConstant.cpp - Emit LLVM Code from Constant Expressions ----===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This contains code to emit Constant Expr nodes as LLVM code.
//
//===----------------------------------------------------------------------===//

#include "CodeGenFunction.h"
#include "CodeGenModule.h"
#include "CGObjCRuntime.h"
#include "clang/AST/APValue.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/RecordLayout.h"
#include "clang/AST/StmtVisitor.h"
#include "clang/Basic/Builtins.h"
#include "llvm/Constants.h"
#include "llvm/Function.h"
#include "llvm/GlobalVariable.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Target/TargetData.h"
using namespace clang;
using namespace CodeGen;

namespace  {

class VISIBILITY_HIDDEN ConstStructBuilder {
  CodeGenModule &CGM;
  CodeGenFunction *CGF;

  bool Packed;  

  unsigned NextFieldOffsetInBytes;
  
  std::vector<llvm::Constant *> Elements;

  ConstStructBuilder(CodeGenModule &CGM, CodeGenFunction *CGF)
    : CGM(CGM), CGF(CGF), Packed(false), NextFieldOffsetInBytes(0) { }

  bool AppendField(const FieldDecl *Field, uint64_t FieldOffset, 
                   const Expr *InitExpr) {
    uint64_t FieldOffsetInBytes = FieldOffset / 8;
    
    assert(NextFieldOffsetInBytes <= FieldOffsetInBytes 
           && "Field offset mismatch!");
    
    // Emit the field.
    llvm::Constant *C = CGM.EmitConstantExpr(InitExpr, Field->getType(), CGF);
    if (!C)
      return false;

    unsigned FieldAlignment = getAlignment(C);
    
    // Round up the field offset to the alignment of the field type.
    uint64_t AlignedNextFieldOffsetInBytes = 
      llvm::RoundUpToAlignment(NextFieldOffsetInBytes, FieldAlignment);
    
    if (AlignedNextFieldOffsetInBytes > FieldOffsetInBytes) {
      std::vector<llvm::Constant *> PackedElements;
      
      assert(!Packed && "Alignment is wrong even with a packed struct!");
      
      // Convert the struct to a packed struct.
      uint64_t ElementOffsetInBytes = 0;
      
      for (unsigned i = 0, e = Elements.size(); i != e; ++i) {
        llvm::Constant *C = Elements[i];
        
        unsigned ElementAlign = 
          CGM.getTargetData().getABITypeAlignment(C->getType());
        uint64_t AlignedElementOffsetInBytes = 
          llvm::RoundUpToAlignment(ElementOffsetInBytes, ElementAlign);
        
        if (AlignedElementOffsetInBytes > ElementOffsetInBytes) {
          // We need some padding.
          uint64_t NumBytes = 
            AlignedElementOffsetInBytes - ElementOffsetInBytes;
          
          const llvm::Type *Ty = llvm::Type::Int8Ty;
          if (NumBytes > 1) 
            Ty = llvm::ArrayType::get(Ty, NumBytes);
          
          llvm::Constant *Padding = llvm::Constant::getNullValue(Ty);
          PackedElements.push_back(Padding);
          ElementOffsetInBytes += getSizeInBytes(Padding);
        }
        
        PackedElements.push_back(C);
        ElementOffsetInBytes += getSizeInBytes(C);
      }

      assert(ElementOffsetInBytes == NextFieldOffsetInBytes &&
             "Packing the struct changed its size!");

      Elements = PackedElements;
      Packed = true;
      AlignedNextFieldOffsetInBytes = NextFieldOffsetInBytes;
    }

    if (AlignedNextFieldOffsetInBytes < FieldOffsetInBytes) {
      // We need to append padding.
      AppendPadding(FieldOffsetInBytes - NextFieldOffsetInBytes);
      
      assert(NextFieldOffsetInBytes == FieldOffsetInBytes &&
             "Did not add enough padding!");
      
      AlignedNextFieldOffsetInBytes = NextFieldOffsetInBytes;
    }
    
    // Add the field.
    Elements.push_back(C);
    NextFieldOffsetInBytes = AlignedNextFieldOffsetInBytes + getSizeInBytes(C);

    return true;
  }
  
  bool AppendBitField(const FieldDecl *Field, uint64_t FieldOffset, 
                      const Expr *InitExpr) {
    llvm::ConstantInt *CI = 
      cast_or_null<llvm::ConstantInt>(CGM.EmitConstantExpr(InitExpr, 
                                                           Field->getType(), 
                                                           CGF));
    // FIXME: Can this ever happen?
    if (!CI)
      return false;
    
    if (FieldOffset > NextFieldOffsetInBytes * 8) {
      // We need to add padding.
      uint64_t NumBytes = 
        llvm::RoundUpToAlignment(FieldOffset - 
                                 NextFieldOffsetInBytes * 8, 8) / 8;
      
      AppendPadding(NumBytes);
    }

    uint64_t FieldSize = 
      Field->getBitWidth()->EvaluateAsInt(CGM.getContext()).getZExtValue();

    llvm::APInt FieldValue = CI->getValue();
    
    // Promote the size of FieldValue if necessary
    // FIXME: This should never occur, but currently it can because initializer
    // constants are cast to bool, and because clang is not enforcing bitfield
    // width limits.
    if (FieldSize > FieldValue.getBitWidth