SILGenStmt.cpp

//===--- SILGenStmt.cpp - Implements Lowering of ASTs -> SIL for Stmts ----===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2015 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See http://swift.org/LICENSE.txt for license information
// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//

#include "SILGen.h"
#include "Scope.h"
#include "Condition.h"
#include "Initialization.h"
#include "LValue.h"
#include "RValue.h"
#include "swift/AST/AST.h"
#include "swift/SIL/SILArgument.h"
#include "swift/AST/DiagnosticsSIL.h"

using namespace swift;
using namespace Lowering;

template<typename...T, typename...U>
static void diagnose(ASTContext &Context, SourceLoc loc, Diag<T...> diag,
                     U &&...args) {
  Context.Diags.diagnose(loc,
                         diag, std::forward<U>(args)...);
}

//===--------------------------------------------------------------------===//
// SILGenFunction visit*Stmt implementation
//===--------------------------------------------------------------------===//

/// emitOrDeleteBlock - If there are branches to the specified basic block,
/// emit it per emitBlock.  If there aren't, then just delete the block - it
/// turns out to have not been needed.
static void emitOrDeleteBlock(SILBuilder &B, SILBasicBlock *BB,
                              SILLocation BranchLoc) {
  if (BB->pred_empty()) {
    // If the block is unused, we don't need it; just delete it.
    BB->eraseFromParent();
  } else {
    // Otherwise, continue emitting code in BB.
    B.emitBlock(BB, BranchLoc);
  }
}

static SILValue emitConditionValue(SILGenFunction &gen, Expr *E) {
  // Sema forces conditions to have Builtin.i1 type, which guarantees this.
  SILValue V;
  {
    FullExpr Scope(gen.Cleanups, CleanupLocation(E));
    V = gen.emitRValue(E).forwardAsSingleValue(gen, E);
  }
  assert(V.getType().castTo<BuiltinIntegerType>()->isFixedWidth(1));

  return V;
}

Condition SILGenFunction::emitCondition(Expr *E,
                                        bool hasFalseCode, bool invertValue,
                                        ArrayRef<SILType> contArgs) {
  assert(B.hasValidInsertionPoint() &&
         "emitting condition at unreachable point");

  return emitCondition(emitConditionValue(*this, E), E,
                       hasFalseCode, invertValue, contArgs);
}

/// Information about a conditional binding.
struct ConditionalBinding {
  PatternBindingDecl *PBD;
  std::unique_ptr<TemporaryInitialization> OptAddr;
};

static std::unique_ptr<TemporaryInitialization>
emitConditionalBindingBuffer(SILGenFunction &gen,
                             StmtCondition cond) {
  if (auto CB = cond.dyn_cast<PatternBindingDecl*>()) {
    assert(CB->isConditional());
    assert(CB->getInit());

    auto &optTL = gen.getTypeLowering(CB->getInit()->getType());
    return gen.emitTemporary(CB, optTL);
  }
  return nullptr;
}

static std::pair<Condition, Optional<ConditionalBinding>>
emitConditionalBinding(SILGenFunction &gen,
                       PatternBindingDecl *CB,
                       std::unique_ptr<TemporaryInitialization> temp,
                       bool hasFalseCode) {
  // Emit the optional value, in its own inner scope.
  {
    FullExpr initScope(gen.Cleanups, CB);
    gen.emitExprInto(CB->getInit(), temp.get());
  }

  // Test for a value in the optional.
  SILValue hasValue = gen.emitDoesOptionalHaveValue(CB, temp->getAddress());
  
  // Emit the condition on the presence of the value.
  Condition C = gen.emitCondition(hasValue, CB, hasFalseCode);
  return {C, ConditionalBinding{CB, std::move(temp)}};
}

static void
enterTrueConditionalBinding(SILGenFunction &gen,
                            const ConditionalBinding &CB) {
  // Bind variables.
  InitializationPtr init
    = gen.emitPatternBindingInitialization(CB.PBD->getPattern());
  
  FullExpr scope(gen.Cleanups, CB.PBD);
  auto &optTL = gen.getTypeLowering(CB.PBD->getPattern()->getType());
  // Take the value out of the temporary buffer into the variables.
  ManagedValue mv = gen.emitGetOptionalValueFrom(CB.PBD,
                         ManagedValue(CB.OptAddr->getAddress(),
                                      CB.OptAddr->getInitializedCleanup()),
                         optTL, SGFContext(init.get()));
  if (!mv.isInContext()) {
    RValue(gen, CB.PBD, CB.PBD->getPattern()->getType()->getCanonicalType(), mv)
      .forwardInto(gen, init.get(), CB.PBD);
  }
  
  // FIXME: Keep the cleanup dormant so we can reactivate it on the false
  // branch?
}

static void
enterFalseConditionalBinding(SILGenFunction &gen,
                             const ConditionalBinding &CB) {
  // Destroy the value in the optional buffer.
  gen.B.emitDestroyAddr(CB.PBD, CB.OptAddr->getAddress());
}

static std::pair<Condition, Optional<ConditionalBinding>>
emitStmtCondition(SILGenFunction &gen, StmtCondition C,
                  std::unique_ptr<TemporaryInitialization> temp,
                   bool hasFalseCode) {
  if (auto E = C.dyn_cast<Expr*>()) {
    return {gen.emitCondition(E, hasFalseCode), Nothing};
  }
  if (auto CB = C.dyn_cast<PatternBindingDecl*>()) {
    return emitConditionalBinding(gen, CB, std::move(temp), hasFalseCode);
  }
  llvm_unreachable("unknown condition");
}

Condition SILGenFunction::emitCondition(SILValue V, SILLocation Loc,
                                        bool hasFalseCode, bool invertValue,
                                        ArrayRef<SILType> contArgs) {
  assert(B.hasValidInsertionPoint() &&
         "emitting condition at unreachable point");

  SILBasicBlock *ContBB = createBasicBlock();
  SILBasicBlock *TrueBB = createBasicBlock();

  for (SILType argTy : contArgs) {
    new (F.getModule()) SILArgument(argTy, ContBB);
  }
  
  SILBasicBlock *FalseBB, *FalseDestBB;
  if (hasFalseCode) {
    FalseBB = FalseDestBB = createBasicBlock();
  } else {
    FalseBB = nullptr;
    FalseDestBB = ContBB;
  }
  if (invertValue)
    B.createCondBranch(Loc, V, FalseDestBB, TrueBB);
  else
    B.createCondBranch(Loc, V, TrueBB, FalseDestBB);
  
  return Condition(TrueBB, FalseBB, ContBB, Loc);
}

void SILGenFunction::visitBraceStmt(BraceStmt *S) {
  // Enter a new scope.
  LexicalScope BraceScope(Cleanups, *this, CleanupLocation(S));
  const unsigned ReturnStmtType   = 0;
  const unsigned ContinueStmtType = 1;
  const unsigned UnknownStmtType  = 2;
  unsigned StmtType = UnknownStmtType;
  
  // There's nothing to do if this is a configuration block.
  if (S->isConfigBlock()) {
    return;
  }

  for (auto &ESD : S->getElements()) {
    
    if (auto S = ESD.dyn_cast<Stmt*>()) {
      if (isa<IfConfigStmt>(S)) {
        continue;
      }
    }
    
    // If we ever reach an unreachable point, stop emitting statements and issue
    // an unreachable code diagnostic. This will need revision if we ever add
    // goto.
    if (!B.hasValidInsertionPoint()) {
      if (StmtType != UnknownStmtType) {
        diagnose(getASTContext(), ESD.getStartLoc(),
                 diag::unreachable_code_after_stmt, StmtType);
      } else {
        diagnose(getASTContext(), ESD.getStartLoc(), diag::unreachable_code);
      }
      return;
    }

    // Process children.
    if (Stmt *S = ESD.dyn_cast<Stmt*>()) {
      visit(S);
      if (isa<ContinueStmt>(S))
        StmtType = ContinueStmtType;
      if (isa<ReturnStmt>(S))
        StmtType = ReturnStmtType;
      
    } else if (Expr *E = ESD.dyn_cast<Expr*>()) {
      FullExpr scope(Cleanups, CleanupLocation(E));
      // If it is convenient to avoid loading the result, don't bother.
      emitRValue(E, SGFContext::AllowPlusZero);

    } else
      visit(ESD.get<Decl*>());
  }
}

namespace {

/// IndirectReturnInitialization - represents initializing an indirect return
/// value.
class IndirectReturnInitialization : public SingleBufferInitialization {
  SILValue address;
public:
  IndirectReturnInitialization(SILValue address)
    : address(address) {}
  
  SILValue getAddressOrNull() const override { return address; }
};

} // end anonymous namespace

void SILGenFunction::emitReturnExpr(SILLocation branchLoc,
                                    Expr *ret) {
  SILValue result;
  if (IndirectReturnAddress) {
    // Indirect return of an address-only value.
    FullExpr scope(Cleanups, CleanupLocation(ret));
    InitializationPtr returnInit(
                       new IndirectReturnInitialization(IndirectReturnAddress));
    emitExprInto(ret, returnInit.get());
  } else {
    // SILValue return.
    FullExpr scope(Cleanups, CleanupLocation(ret));
    RValue resultRValue = emitRValue(ret);
    if (!resultRValue.getType()->isVoid()) {
      result = std::move(resultRValue).forwardAsSingleValue(*this, ret);
    }
  }
  Cleanups.emitBranchAndCleanups(ReturnDest, branchLoc,
                                 result ? result : ArrayRef<SILValue>{});
}

void SILGenFunction::visitReturnStmt(ReturnStmt *S) {
  CurrentSILLoc = S;
  ReturnLocation Loc(S);

  SILValue ArgV;
  if (!S->hasResult())
    // Void return.
    Cleanups.emitBranchAndCleanups(ReturnDest, Loc);
  else
    emitReturnExpr(Loc, S->getResult());
}

void SILGenFunction::visitIfStmt(IfStmt *S) {
  Scope condBufferScope(Cleanups, S);
  auto condBuffer = emitConditionalBindingBuffer(*this, S->getCond());
  
  // We need a false branch if we have an 'else' block or if we have a
  // pattern binding, to clean up the unconsumed optional value.
  bool hasBindings = condBuffer.get();
  auto CondPair = emitStmtCondition(*this, S->getCond(), std::move(condBuffer),
                                    S->getElseStmt() != nullptr
                                      || hasBindings);
  auto &Cond = CondPair.first;
  auto &CondBinding = CondPair.second;
  
  if (Cond.hasTrue()) {
    Cond.enterTrue(B);
    {
      // Enter a scope for pattern variables.
      Scope trueScope(Cleanups, S);
      if (CondBinding)
        enterTrueConditionalBinding(*this, *CondBinding);
      visit(S->getThenStmt());
    }
    Cond.exitTrue(B);
  }
  
  if (Cond.hasFalse()) {
    Cond.enterFalse(B);
    if (CondBinding)
      enterFalseConditionalBinding(*this, *CondBinding);
    if (S->getElseStmt())
      visit(S->getElseStmt());
    Cond.exitFalse(B);
  }
  
  Cond.complete(B);
}

void SILGenFunction::visitIfConfigStmt(IfConfigStmt *S) {
  // Active members are attached to the enclosing declaration, so there's no
  // need to walk anything within.
}

void SILGenFunction::visitWhileStmt(WhileStmt *S) {
  Scope condBufferScope(Cleanups, S);
  // Allocate a buffer for pattern binding conditions outside the loop.
  auto condBuffer = emitConditionalBindingBuffer(*this, S->getCond());
  
  // Create a new basic block and jump into it.
  SILBasicBlock *LoopBB = createBasicBlock();
  B.emitBlock(LoopBB, S);
  
  // Evaluate the condition with the false edge leading directly
  // to the continuation block.
  auto CondPair = emitStmtCondition(*this, S->getCond(), std::move(condBuffer),
                                    /*hasFalseCode*/ false);
  auto &Cond = CondPair.first;
  auto &CondBinding = CondPair.second;

  // Set the destinations for 'break' and 'continue'
  SILBasicBlock *EndBB = createBasicBlock();
  BreakDestStack.emplace_back(EndBB, getCleanupsDepth(),
                              CleanupLocation(S->getBody()));
  ContinueDestStack.emplace_back(LoopBB, getCleanupsDepth(),
                                 CleanupLocation(S->getBody()));

  // If there's a true edge, emit the body in it.
  if (Cond.hasTrue()) {
    Cond.enterTrue(B);
    {
      // Enter a scope for pattern variables.
      Scope trueScope(Cleanups, S);
      if (CondBinding)
        enterTrueConditionalBinding(*this, *CondBinding);
      
      visit(S->getBody());
      if (B.hasValidInsertionPoint()) {
        // Associate the loop body's closing brace with this branch.
        RegularLocation L(S->getBody());
        L.pointToEnd();
        B.createBranch(L, LoopBB);
      }
    }
    Cond.exitTrue(B);
  }
  
  // Complete the conditional execution.
  Cond.complete(B);
  if (CondBinding)
    enterFalseConditionalBinding(*this, *CondBinding);
  
  emitOrDeleteBlock(B, EndBB, S);
  BreakDestStack.pop_back();
  ContinueDestStack.pop_back();
}

void SILGenFunction::visitDoWhileStmt(DoWhileStmt *S) {
  // Create a new basic block and jump into it.
  SILBasicBlock *LoopBB = createBasicBlock();
  B.emitBlock(LoopBB, S);
  
  // Set the destinations for 'break' and 'continue'
  SILBasicBlock *EndBB = createBasicBlock();
  SILBasicBlock *CondBB = createBasicBlock();
  BreakDestStack.emplace_back(EndBB, getCleanupsDepth(),
                              CleanupLocation(S->getBody()));
  ContinueDestStack.emplace_back(CondBB, getCleanupsDepth(),
                                 CleanupLocation(S->getBody()));
  
  // Emit the body, which is always evaluated the first time around.
  visit(S->getBody());

  // Let's not differ from C99 6.8.5.2: "The evaluation of the controlling
  // expression takes place after each execution of the loop body."
  emitOrDeleteBlock(B, CondBB, S);

  if (B.hasValidInsertionPoint()) {
    // Evaluate the condition with the false edge leading directly
    // to the continuation block.
    Condition Cond = emitCondition(S->getCond(), /*hasFalseCode*/ false);
    
    Cond.enterTrue(B);
    if (B.hasValidInsertionPoint()) {
      B.createBranch(S->getCond(), LoopBB);
    }
    
    Cond.exitTrue(B);
    // Complete the conditional execution.
    Cond.complete(B);
  }
  
  emitOrDeleteBlock(B, EndBB, S);
  BreakDestStack.pop_back();
  ContinueDestStack.pop_back();
}

void SILGenFunction::visitForStmt(ForStmt *S) {
  // Enter a new scope.
  Scope ForScope(Cleanups, CleanupLocation(S));
  
  // Emit any local 'var' variables declared in the initializer.
  for (auto D : S->getInitializerVarDecls())
    visit(D);
  
  if (auto *Initializer = S->getInitializer().getPtrOrNull()) {
    FullExpr Scope(Cleanups, CleanupLocation(Initializer));
    // If it is convenient to avoid loading the init expr, don't bother.
    emitRValue(Initializer, SGFContext::AllowPlusZero);
  }
  
  // If we ever reach an unreachable point, stop emitting statements.
  // This will need revision if we ever add goto.
  if (!B.hasValidInsertionPoint()) return;
  
  // Create a new basic block and jump into it.
  SILBasicBlock *LoopBB = createBasicBlock();
  B.emitBlock(LoopBB, S);
  
  // Set the destinations for 'break' and 'continue'
  SILBasicBlock *IncBB = createBasicBlock();
  SILBasicBlock *EndBB = createBasicBlock();
  BreakDestStack.emplace_back(EndBB, getCleanupsDepth(),
                              CleanupLocation(S->getBody()));
  ContinueDestStack.emplace_back(IncBB, getCleanupsDepth(),
                                 CleanupLocation(S->getBody()));
  
  // Evaluate the condition with the false edge leading directly
  // to the continuation block.
  Condition Cond = S->getCond().isNonNull() ?
    emitCondition(S->getCond().get(), /*hasFalseCode*/ false) :
    Condition(LoopBB, 0, 0, S); // Infinite loop.
  
  // If there's a true edge, emit the body in it.
  if (Cond.hasTrue()) {
    Cond.enterTrue(B);
    visit(S->getBody());
    
    emitOrDeleteBlock(B, IncBB, S);
    
    if (B.hasValidInsertionPoint() && S->getIncrement().isNonNull()) {
      FullExpr Scope(Cleanups, CleanupLocation(S->getIncrement().get()));
      // Don't bother loading the result of the increment expression.
      emitRValue(S->getIncrement().get(), SGFContext::AllowPlusZero);
    }
    
    if (B.hasValidInsertionPoint()) {
      // Accosiate the loop body's closing brace with this branch.
      RegularLocation L(S->getBody());
      L.pointToEnd();
      B.createBranch(L, LoopBB);
    }
    Cond.exitTrue(B);
  }
  
  // Complete the conditional execution.
  Cond.complete(B);
  
  emitOrDeleteBlock(B, EndBB, S);
  BreakDestStack.pop_back();
  ContinueDestStack.pop_back();
}

namespace {
  
/// NextForEachValueInitialization - initialization for the 'next' value buffer
/// used during for each loop codegen.

class NextForEachValueInitialization : public SingleBufferInitialization {
  SILValue address;
public:
  NextForEachValueInitialization(SILValue address)
    : address(address) {}
  
  SILValue getAddressOrNull() const override { return address; }
};

} // end anonymous namespace


void SILGenFunction::visitForEachStmt(ForEachStmt *S) {
  // Emit the 'generator' variable that we'll be using for iteration.
  Scope OuterForScope(Cleanups, CleanupLocation(S));
  visitPatternBindingDecl(S->getGenerator());
  
  // If we ever reach an unreachable point, stop emitting statements.
  // This will need revision if we ever add goto.
  if (!B.hasValidInsertionPoint()) return;
  
  // Create a stack allocation to hold values out of the generator.
  // This will be initialized on every entry into the loop header and consumed
  // by the loop body. On loop exit, the terminating value will be in the
  // buffer.
  auto optTy = S->getGeneratorNext()->getType()->getCanonicalType();
  auto valTy = optTy.getAnyOptionalObjectType();
  auto &optTL = getTypeLowering(optTy);
  SILValue nextBuf = emitTemporaryAllocation(S, optTL.getLoweredType());
  
  // Create a new basic block and jump into it.
  SILBasicBlock *LoopBB = createBasicBlock();
  B.emitBlock(LoopBB, S);
  
  // Set the destinations for 'break' and 'continue'.
  SILBasicBlock *EndBB = createBasicBlock();
  BreakDestStack.emplace_back(EndBB,
                              getCleanupsDepth(),
                              CleanupLocation(S->getBody()));
  ContinueDestStack.emplace_back(LoopBB, getCleanupsDepth(),
                                 CleanupLocation(S->getBody()));
  
  // Advance the generator.  Use a scope to ensure that any temporary stack
  // allocations in the subexpression are immediately released.
  {
    Scope InnerForScope(Cleanups, CleanupLocation(S->getGeneratorNext()));
    InitializationPtr nextInit(new NextForEachValueInitialization(nextBuf));
    emitExprInto(S->getGeneratorNext(), nextInit.get());
    nextInit->finishInitialization(*this);
  }
  
  // Continue if the value is present.
  Condition Cond = emitCondition(
         emitDoesOptionalHaveValue(S, nextBuf), S,
         /*hasFalseCode=*/false, /*invertValue=*/false);

  if (Cond.hasTrue()) {
    Cond.enterTrue(B);
    
    // Emit the loop body.
    // The declared variable(s) for the current element are destroyed
    // at the end of each loop iteration.
    {
      Scope InnerForScope(Cleanups, CleanupLocation(S->getBody()));
      InitializationPtr initLoopVars
        = emitPatternBindingInitialization(S->getPattern());
      ManagedValue val = emitGetOptionalValueFrom(S,
                               ManagedValue::forUnmanaged(nextBuf),
                               optTL,
                               SGFContext(initLoopVars.get()));
      if (!val.isInContext())
        RValue(*this, S, valTy, val).forwardInto(*this, initLoopVars.get(), S);
      visit(S->getBody());
    }
    
    // Loop back to the header.
    if (B.hasValidInsertionPoint()) {
      // Associate the loop body's closing brace with this branch.
      RegularLocation L(S->getBody());
      L.pointToEnd();
      B.createBranch(L, LoopBB);
    }
    Cond.exitTrue(B);
  }
  
  // Complete the conditional execution.
  Cond.complete(B);
  
  emitOrDeleteBlock(B, EndBB, S);
  BreakDestStack.pop_back();
  ContinueDestStack.pop_back();
  
  // Destroy the last value that came out of the generator.
  B.emitDestroyAddr(S, nextBuf);
}

void SILGenFunction::visitBreakStmt(BreakStmt *S) {
  CurrentSILLoc = S;
  Cleanups.emitBranchAndCleanups(BreakDestStack.back(), S);
}

void SILGenFunction::visitContinueStmt(ContinueStmt *S) {
  CurrentSILLoc = S;
  Cleanups.emitBranchAndCleanups(ContinueDestStack.back(), S);
}

void SILGenFunction::visitSwitchStmt(SwitchStmt *S) {
  // Implemented in SILGenPattern.cpp.
  emitSwitchStmt(S);
}

void SILGenFunction::visitCaseStmt(CaseStmt *S) {
  llvm_unreachable("cases should be lowered as part of switch stmt");
}

void SILGenFunction::visitFallthroughStmt(FallthroughStmt *S) {
  // Implemented in SILGenPattern.cpp.
  emitSwitchFallthrough(S);
}

void SILGenModule::visitIfConfigDecl(IfConfigDecl *ICD) {
  // Nothing to do for these kinds of decls - anything active has been added
  // to the enclosing declaration.
}

//===--------------------------------------------------------------------===//
// SILGenModule visitTopLevelCodeDecl implementation
//===--------------------------------------------------------------------===//

void SILGenModule::visitTopLevelCodeDecl(TopLevelCodeDecl *td) {
  // Emit top-level statements and expressions into the toplevel function until
  // we hit an unreachable point.
  assert(TopLevelSGF && "top-level code in a non-main source file!");
// TODO:
  if (!TopLevelSGF->B.hasValidInsertionPoint())
    return;
  
  TopLevelSGF->visit(td->getBody());
}