path: root/CodeGen/CGStmt.cpp

//===--- CGStmt.cpp - Emit LLVM Code from Statements ----------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file was developed by Chris Lattner and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This contains code to emit Stmt nodes as LLVM code.
//
//===----------------------------------------------------------------------===//

#include "CodeGenFunction.h"
#include "clang/AST/AST.h"
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Function.h"
using namespace clang;
using namespace CodeGen;

//===----------------------------------------------------------------------===//
//                              Statement Emission
//===----------------------------------------------------------------------===//

void CodeGenFunction::EmitStmt(const Stmt *S) {
  assert(S && "Null statement?");
  
  switch (S->getStmtClass()) {
  default:
    // Must be an expression in a stmt context.  Emit the value (to get
    // side-effects) and ignore the result.
    if (const Expr *E = dyn_cast<Expr>(S)) {
      if (!hasAggregateLLVMType(E->getType()))
        EmitScalarExpr(E);
      else if (E->getType()->isComplexType())
        EmitComplexExpr(E);
      else
        EmitAggExpr(E, 0, false);
    } else {
      WarnUnsupported(S, "statement");
    }
    break;
  case Stmt::NullStmtClass: break;
  case Stmt::CompoundStmtClass: EmitCompoundStmt(cast<CompoundStmt>(*S)); break;
  case Stmt::LabelStmtClass:    EmitLabelStmt(cast<LabelStmt>(*S));       break;
  case Stmt::GotoStmtClass:     EmitGotoStmt(cast<GotoStmt>(*S));         break;

  case Stmt::IfStmtClass:       EmitIfStmt(cast<IfStmt>(*S));             break;
  case Stmt::WhileStmtClass:    EmitWhileStmt(cast<WhileStmt>(*S));       break;
  case Stmt::DoStmtClass:       EmitDoStmt(cast<DoStmt>(*S));             break;
  case Stmt::ForStmtClass:      EmitForStmt(cast<ForStmt>(*S));           break;
    
  case Stmt::ReturnStmtClass:   EmitReturnStmt(cast<ReturnStmt>(*S));     break;
  case Stmt::DeclStmtClass:     EmitDeclStmt(cast<DeclStmt>(*S));         break;
      
  case Stmt::BreakStmtClass:    EmitBreakStmt();                          break;
  case Stmt::ContinueStmtClass: EmitContinueStmt();                       break;
  case Stmt::SwitchStmtClass:   EmitSwitchStmt(cast<SwitchStmt>(*S));     break;
  case Stmt::DefaultStmtClass:  EmitDefaultStmt(cast<DefaultStmt>(*S));   break;
  case Stmt::CaseStmtClass:     EmitCaseStmt(cast<CaseStmt>(*S));         break;
  }
}

/// EmitCompoundStmt - Emit a compound statement {..} node.  If GetLast is true,
/// this captures the expression result of the last sub-statement and returns it
/// (for use by the statement expression extension).
RValue CodeGenFunction::EmitCompoundStmt(const CompoundStmt &S, bool GetLast,
                                         llvm::Value *AggLoc, bool isAggVol) {
  // FIXME: handle vla's etc.
  if (S.body_empty() || !isa<Expr>(S.body_back())) GetLast = false;
  
  for (CompoundStmt::const_body_iterator I = S.body_begin(),
       E = S.body_end()-GetLast; I != E; ++I)
    EmitStmt(*I);
  
  
  if (!GetLast)
    return RValue::get(0);
  
  return EmitAnyExpr(cast<Expr>(S.body_back()), AggLoc);
}

void CodeGenFunction::EmitBlock(llvm::BasicBlock *BB) {
  // Emit a branch from this block to the next one if this was a real block.  If
  // this was just a fall-through block after a terminator, don't emit it.
  llvm::BasicBlock *LastBB = Builder.GetInsertBlock();
  
  if (LastBB->getTerminator()) {
    // If the previous block is already terminated, don't touch it.
  } else if (LastBB->empty() && LastBB->getValueName() == 0) {
    // If the last block was an empty placeholder, remove it now.
    // TODO: cache and reuse these.
    Builder.GetInsertBlock()->eraseFromParent();
  } else {
    // Otherwise, create a fall-through branch.
    Builder.CreateBr(BB);
  }
  CurFn->getBasicBlockList().push_back(BB);
  Builder.SetInsertPoint(BB);
}

void CodeGenFunction::EmitLabelStmt(const LabelStmt &S) {
  llvm::BasicBlock *NextBB = getBasicBlockForLabel(&S);
  
  EmitBlock(NextBB);
  EmitStmt(S.getSubStmt());
}

void CodeGenFunction::EmitGotoStmt(const GotoStmt &S) {
  Builder.CreateBr(getBasicBlockForLabel(S.getLabel()));
  
  // Emit a block after the branch so that dead code after a goto has some place
  // to go.
  Builder.SetInsertPoint(new llvm::BasicBlock("", CurFn));
}

void CodeGenFunction::EmitIfStmt(const IfStmt &S) {
  // C99 6.8.4.1: The first substatement is executed if the expression compares
  // unequal to 0.  The condition must be a scalar type.
  llvm::Value *BoolCondVal = EvaluateExprAsBool(S.getCond());
  
  llvm::BasicBlock *ContBlock = new llvm::BasicBlock("ifend");
  llvm::BasicBlock *ThenBlock = new llvm::BasicBlock("ifthen");
  llvm::BasicBlock *ElseBlock = ContBlock;
  
  if (S.getElse())
    ElseBlock = new llvm::BasicBlock("ifelse");
  
  // Insert the conditional branch.
  Builder.CreateCondBr(BoolCondVal, ThenBlock, ElseBlock);
  
  // Emit the 'then' code.
  EmitBlock(ThenBlock);
  EmitStmt(S.getThen());
  llvm::BasicBlock *BB = Builder.GetInsertBlock();
  if (isDummyBlock(BB)) {
    BB->eraseFromParent();
    Builder.SetInsertPoint(ThenBlock);
  }
  else
    Builder.CreateBr(ContBlock);
  
  // Emit the 'else' code if present.
  if (const Stmt *Else = S.getElse()) {
    EmitBlock(ElseBlock);
    EmitStmt(Else);
    llvm::BasicBlock *BB = Builder.GetInsertBlock();
    if (isDummyBlock(BB)) {
      BB->eraseFromParent();
      Builder.SetInsertPoint(ElseBlock);
    }
    else
      Builder.CreateBr(ContBlock);
  }
  
  // Emit the continuation block for code after the if.
  EmitBlock(ContBlock);
}

void CodeGenFunction::EmitWhileStmt(const WhileStmt &S) {
  // Emit the header for the loop, insert it, which will create an uncond br to
  // it.
  llvm::BasicBlock *LoopHeader = new llvm::BasicBlock("whilecond");
  EmitBlock(LoopHeader);
  
  // Evaluate the conditional in the while header.  C99 6.8.5.1: The evaluation
  // of the controlling expression takes place before each execution of the loop
  // body. 
  llvm::Value *BoolCondVal = EvaluateExprAsBool(S.getCond());

  // while(1) is common, avoid extra exit blocks.  Be sure
  // to correctly handle break/continue though.
  bool EmitBoolCondBranch = true;
  if (llvm::ConstantInt *C = dyn_cast<llvm::ConstantInt>(BoolCondVal)) 
    if (C->isOne())
      EmitBoolCondBranch = false;
  
  // Create an exit block for when the condition fails, create a block for the
  // body of the loop.
  llvm::BasicBlock *ExitBlock = new llvm::BasicBlock("whileexit");
  llvm::BasicBlock *LoopBody  = new llvm::BasicBlock("whilebody");
  
  // As long as the condition is true, go to the loop body.
  if (EmitBoolCondBranch)
    Builder.CreateCondBr(BoolCondVal, LoopBody, ExitBlock);

  // Store the blocks to use for break and continue.
  BreakContinueStack.push_back(BreakContinue(ExitBlock, LoopHeader));
  
  // Emit the loop body.
  EmitBlock(LoopBody);
  EmitStmt(S.getBody());

  BreakContinueStack.pop_back();
  
  // Cycle to the condition.
  Builder.CreateBr(LoopHeader);
  
  // Emit the exit block.
  EmitBlock(ExitBlock);

  // If LoopHeader is a simple forwarding block then eliminate it.
  if (!EmitBoolCondBranch 
      && &LoopHeader->front() == LoopHeader->getTerminator()) {
    LoopHeader->replaceAllUsesWith(LoopBody);
    LoopHeader->getTerminator()->eraseFromParent();
    LoopHeader->eraseFromParent();
  }
}

void CodeGenFunction::EmitDoStmt(const DoStmt &S) {
  // Emit the body for the loop, insert it, which will create an uncond br to
  // it.
  llvm::BasicBlock *LoopBody =