path: root/lib/CodeGen/CodeGenFunction.cpp

//===--- CodeGenFunction.cpp - Emit LLVM Code from ASTs for a Function ----===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This coordinates the per-function state used while generating code.
//
//===----------------------------------------------------------------------===//

#include "CodeGenFunction.h"
#include "CodeGenModule.h"
#include "CGDebugInfo.h"
#include "clang/Basic/TargetInfo.h"
#include "clang/AST/APValue.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/Decl.h"
#include "llvm/Support/CFG.h"
using namespace clang;
using namespace CodeGen;

CodeGenFunction::CodeGenFunction(CodeGenModule &cgm) 
  : CGM(cgm), Target(CGM.getContext().Target), SwitchInsn(NULL), 
    CaseRangeBlock(NULL) {
    LLVMIntTy = ConvertType(getContext().IntTy);
    LLVMPointerWidth = Target.getPointerWidth(0);
}

ASTContext &CodeGenFunction::getContext() const {
  return CGM.getContext();
}


llvm::BasicBlock *CodeGenFunction::getBasicBlockForLabel(const LabelStmt *S) {
  llvm::BasicBlock *&BB = LabelMap[S];
  if (BB) return BB;
  
  // Create, but don't insert, the new block.
  return BB = createBasicBlock(S->getName());
}

llvm::Constant *
CodeGenFunction::GetAddrOfStaticLocalVar(const VarDecl *BVD) {
  return cast<llvm::Constant>(LocalDeclMap[BVD]);
}

llvm::Value *CodeGenFunction::GetAddrOfLocalVar(const VarDecl *VD)
{
  return LocalDeclMap[VD];
}

const llvm::Type *CodeGenFunction::ConvertType(QualType T) {
  return CGM.getTypes().ConvertType(T);
}

bool CodeGenFunction::isObjCPointerType(QualType T) {
  // All Objective-C types are pointers.
  return T->isObjCInterfaceType() ||
    T->isObjCQualifiedInterfaceType() || T->isObjCQualifiedIdType();
}

bool CodeGenFunction::hasAggregateLLVMType(QualType T) {
  return !isObjCPointerType(T) &&!T->isRealType() && !T->isPointerLikeType() &&
    !T->isVoidType() && !T->isVectorType() && !T->isFunctionType();
}

void CodeGenFunction::FinishFunction(SourceLocation EndLoc) {
  // Finish emission of indirect switches.
  EmitIndirectSwitches();

  assert(BreakContinueStack.empty() &&
         "mismatched push/pop in break/continue stack!");

  // Emit function epilog (to return). This has the nice side effect
  // of also automatically handling code that falls off the end.
  EmitBlock(ReturnBlock);

  // Emit debug descriptor for function end.
  if (CGDebugInfo *DI = CGM.getDebugInfo()) {
    DI->setLocation(EndLoc);
    DI->EmitRegionEnd(CurFn, Builder);
  }

  EmitFunctionEpilog(FnRetTy, ReturnValue);

  // Remove the AllocaInsertPt instruction, which is just a convenience for us.
  AllocaInsertPt->eraseFromParent();
  AllocaInsertPt = 0;
}

void CodeGenFunction::StartFunction(const Decl *D, QualType RetTy, 
                                    llvm::Function *Fn,
                                    const FunctionArgList &Args,
                                    SourceLocation StartLoc) {
  CurFuncDecl = D;
  FnRetTy = RetTy;
  CurFn = Fn;
  assert(CurFn->isDeclaration() && "Function already has body?");

  llvm::BasicBlock *EntryBB = createBasicBlock("entry", CurFn);

  // Create a marker to make it easy to insert allocas into the entryblock
  // later.  Don't create this with the builder, because we don't want it
  // folded.
  llvm::Value *Undef = llvm::UndefValue::get(llvm::Type::Int32Ty);
  AllocaInsertPt = new llvm::BitCastInst(Undef, llvm::Type::Int32Ty, "allocapt",
                                         EntryBB);

  ReturnBlock = createBasicBlock("return");
  ReturnValue = 0;
  if (!RetTy->isVoidType())
    ReturnValue = CreateTempAlloca(ConvertType(RetTy), "retval");
    
  Builder.SetInsertPoint(EntryBB);
  
  // Emit subprogram debug descriptor.
  // FIXME: The cast here is a huge hack.
  if (CGDebugInfo *DI = CGM.getDebugInfo()) {
    DI->setLocation(StartLoc);
    if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(D)) {
      DI->EmitFunctionStart(FD->getIdentifierName(), RetTy, CurFn, Builder);
    } else {
      // Just use LLVM function name.
      DI->EmitFunctionStart(Fn->getName().c_str(), 
                            RetTy, CurFn, Builder);
    }
  }

  EmitFunctionProlog(CurFn, FnRetTy, Args);
}

void CodeGenFunction::GenerateCode(const FunctionDecl *FD,
                                   llvm::Function *Fn) {
  FunctionArgList Args;
  if (FD->getNumParams()) {
    const FunctionTypeProto* FProto = FD->getType()->getAsFunctionTypeProto();
    assert(FProto && "Function def must have prototype!");

    for (unsigned i = 0, e = FD->getNumParams(); i != e; ++i)
      Args.push_back(std::make_pair(FD->getParamDecl(i), 
                                    FProto->getArgType(i)));
  }

  StartFunction(FD, FD->getResultType(), Fn, Args,
                cast<CompoundStmt>(FD->getBody())->getLBracLoc());

  EmitStmt(FD->getBody());
  
  const CompoundStmt *S = dyn_cast<CompoundStmt>(FD->getBody());
  if (S) {
    FinishFunction(S->getRBracLoc());
  } else {
    FinishFunction();
  }
}

/// ContainsLabel - Return true if the statement contains a label in it.  If
/// this statement is not executed normally, it not containing a label means
/// that we can just remove the code.
bool CodeGenFunction::ContainsLabel(const Stmt *S, bool IgnoreCaseStmts) {
  // Null statement, not a label!
  if (S == 0) return false;
  
  // If this is a label, we have to emit the code, consider something like:
  // if (0) {  ...  foo:  bar(); }  goto foo;
  if (isa<LabelStmt>(S))
    return true;
  
  // If this is a case/default statement, and we haven't seen a switch, we have
  // to emit the code.
  if (isa<SwitchCase>(S) && !IgnoreCaseStmts)
    return true;
  
  // If this is a switch statement, we want to ignore cases below it.
  if (isa<SwitchStmt>(S))
    IgnoreCaseStmts = true;
  
  // Scan subexpressions for verboten labels.
  for (Stmt::const_child_iterator I = S->child_begin(), E = S->child_end();
       I != E; ++I)
    if (ContainsLabel(*I, IgnoreCaseStmts))
      return true;
  
  return false;
}


/// ConstantFoldsToSimpleInteger - If the sepcified expression does not fold to
/// a constant, or if it does but contains a label, return 0.  If it constant
/// folds to 'true' and does not contain a label, return 1, if it constant folds
/// to 'false' and does not contain a label, return -1.
int CodeGenFunction::ConstantFoldsToSimpleInteger(const Expr *Cond) {
  APValue V;
  
  // FIXME: Rename and handle conversion of other evaluatable things
  // to bool.
  bool isEvaluated;
  if (!Cond->Evaluate(V, getContext(), &isEvaluated) || !V.isInt() ||
      !isEvaluated)
    return 0;  // Not foldable, not integer or not fully evaluatable.
  
  if (CodeGenFunction::ContainsLabel(Cond))
    return 0;  // Contains a label.
  
  return V.getInt().getBoolValue() ? 1 : -1;
}


/// EmitBranchOnBoolExpr - Emit a branch on a boolean condition (e.g. for an if
/// statement) to the specified blocks.  Based on the condition, this might try
/// to simplify the codegen of the conditional based on the branch.
///
void CodeGenFunction::EmitBranchOnBoolExpr(const Expr *Cond,
                                           llvm::BasicBlock *TrueBlock,
                                           llvm::BasicBlock *FalseBlock) {
  if (const ParenExpr *PE = dyn_cast<ParenExpr>(Cond))
    return EmitBranchOnBoolExpr(PE->getSubExpr(), TrueBlock, FalseBlock);
  
  if (const BinaryOperator *CondBOp = dyn_cast<BinaryOperator>(Cond)) {
    // Handle X && Y in a condition.
    if (CondBOp->getOpcode() == BinaryOperator::LAnd) {
      // If we have "1 && X", simplify the code.  "0 && X" would have constant
      // folded if the case was simple enough.
      if (ConstantFoldsToSimpleInteger(CondBOp->getLHS()) == 1) {
        // br(1 && X) -> br(X).
        return EmitBranchOnBoolExpr(CondBOp->getRHS(), TrueBlock, FalseBlock);
      }
      
      // If we have "X && 1", simplify the code to use an uncond branch.
      // "X && 0" would have been constant folded to 0.
      if (ConstantFoldsToSimpleInteger(CondBOp->getRHS()) == 1) {
        // br(X && 1) -> br(X).
        return EmitBranchOnBoolExpr(CondBOp->getLHS(), TrueBlock, FalseBlock);
      }
      
      // Emit the LHS as a conditional.  If the LHS conditional is false, we
      // want to jump to the FalseBlock.
      llvm::BasicBlock *LHSTrue = createBasicBlock("land.lhs.true");
      EmitBranchOnBoolExpr(CondBOp->getLHS(),