lib/Sema/SemaAttr.cpp

//===--- SemaAttr.cpp - Semantic Analysis for Attributes ------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements semantic analysis for non-trivial attributes and
// pragmas.
//
//===----------------------------------------------------------------------===//

#include "Sema.h"
#include "clang/AST/Expr.h"
using namespace clang;

//===----------------------------------------------------------------------===//
// Pragma Packed
//===----------------------------------------------------------------------===//

namespace {
  /// PragmaPackStack - Simple class to wrap the stack used by #pragma
  /// pack.
  class PragmaPackStack {
    typedef std::vector< std::pair<unsigned, IdentifierInfo*> > stack_ty;

    /// Alignment - The current user specified alignment.
    unsigned Alignment;

    /// Stack - Entries in the #pragma pack stack, consisting of saved
    /// alignments and optional names.
    stack_ty Stack;
    
  public:  
    PragmaPackStack() : Alignment(0) {}

    void setAlignment(unsigned A) { Alignment = A; }
    unsigned getAlignment() { return Alignment; }

    /// push - Push the current alignment onto the stack, optionally
    /// using the given \arg Name for the record, if non-zero.
    void push(IdentifierInfo *Name) {
      Stack.push_back(std::make_pair(Alignment, Name));
    }

    /// pop - Pop a record from the stack and restore the current
    /// alignment to the previous value. If \arg Name is non-zero then
    /// the first such named record is popped, otherwise the top record
    /// is popped. Returns true if the pop succeeded.
    bool pop(IdentifierInfo *Name);
  };
}  // end anonymous namespace.

bool PragmaPackStack::pop(IdentifierInfo *Name) {
  if (Stack.empty())
    return false;
  
  // If name is empty just pop top.
  if (!Name) {
    Alignment = Stack.back().first;
    Stack.pop_back();
    return true;
  } 
  
  // Otherwise, find the named record.
  for (unsigned i = Stack.size(); i != 0; ) {
    --i;
    if (Stack[i].second == Name) {
      // Found it, pop up to and including this record.
      Alignment = Stack[i].first;
      Stack.erase(Stack.begin() + i, Stack.end());
      return true;
    }
  }
  
  return false;
}


/// FreePackedContext - Deallocate and null out PackContext.
void Sema::FreePackedContext() {
  delete static_cast<PragmaPackStack*>(PackContext);
  PackContext = 0;
}

/// getPragmaPackAlignment() - Return the current alignment as specified by
/// the current #pragma pack directive, or 0 if none is currently active.
unsigned Sema::getPragmaPackAlignment() const {
  if (PackContext)
    return static_cast<PragmaPackStack*>(PackContext)->getAlignment();
  return 0;
}

void Sema::ActOnPragmaPack(PragmaPackKind Kind, IdentifierInfo *Name, 
                           ExprTy *alignment, SourceLocation PragmaLoc, 
                           SourceLocation LParenLoc, SourceLocation RParenLoc) {
  Expr *Alignment = static_cast<Expr *>(alignment);

  // If specified then alignment must be a "small" power of two.
  unsigned AlignmentVal = 0;
  if (Alignment) {
    llvm::APSInt Val;
    
    // pack(0) is like pack(), which just works out since that is what
    // we use 0 for in PackAttr.
    if (!Alignment->isIntegerConstantExpr(Val, Context) ||
        !(Val == 0 || Val.isPowerOf2()) ||
        Val.getZExtValue() > 16) {
      Diag(PragmaLoc, diag::warn_pragma_pack_invalid_alignment);
      Alignment->Destroy(Context);
      return; // Ignore
    }

    AlignmentVal = (unsigned) Val.getZExtValue();
  }
  
  if (PackContext == 0)
    PackContext = new PragmaPackStack();
  
  PragmaPackStack *Context = static_cast<PragmaPackStack*>(PackContext);
  
  switch (Kind) {
  case Action::PPK_Default: // pack([n])
    Context->setAlignment(AlignmentVal);
    break;

  case Action::PPK_Show: // pack(show)
    // Show the current alignment, making sure to show the right value
    // for the default.
    AlignmentVal = Context->getAlignment();
    // FIXME: This should come from the target.
    if (AlignmentVal == 0)
      AlignmentVal = 8;
    Diag(PragmaLoc, diag::warn_pragma_pack_show) << AlignmentVal;
    break;

  case Action::PPK_Push: // pack(push [, id] [, [n])
    Context->push(Name);
    // Set the new alignment if specified.
    if (Alignment)
      Context->setAlignment(AlignmentVal);    
    break;

  case Action::PPK_Pop: // pack(pop [, id] [,  n])
    // MSDN, C/C++ Preprocessor Reference > Pragma Directives > pack:
    // "#pragma pack(pop, identifier, n) is undefined"
    if (Alignment && Name)
      Diag(PragmaLoc, diag::warn_pragma_pack_pop_identifer_and_alignment);    
    
    // Do the pop.
    if (!Context->pop(Name)) {
      // If a name was specified then failure indicates the name
      // wasn't found. Otherwise failure indicates the stack was
      // empty.
      Diag(PragmaLoc, diag::warn_pragma_pack_pop_failed)
        << (Name ? "no record matching name" : "stack empty");

      // FIXME: Warn about popping named records as MSVC does.
    } else {
      // Pop succeeded, set the new alignment if specified.
      if (Alignment)
        Context->setAlignment(AlignmentVal);
    }
    break;

  default:
    assert(0 && "Invalid #pragma pack kind.");
  }
}

void Sema::ActOnPragmaUnused(ExprTy **Exprs, unsigned NumExprs,
                             SourceLocation PragmaLoc,
                             SourceLocation LParenLoc,
                             SourceLocation RParenLoc) {
  
  // Verify that all of the expressions are valid before
  // modifying the attributes of any referenced decl.
  Expr *ErrorExpr = 0;
  
  for (unsigned i = 0; i < NumExprs; ++i) {  
    Expr *Ex = (Expr*) Exprs[i];
    if (!isa<DeclRefExpr>(Ex)) {
      ErrorExpr = Ex;
      break;
    }

    Decl *d = cast<DeclRefExpr>(Ex)->getDecl();;

    if (!isa<VarDecl>(d) || !cast<VarDecl>(d)->hasLocalStorage()) {
      ErrorExpr = Ex;
      break;
    }
  }
  
  // Delete the expressions if we encountered any error.
  if (ErrorExpr) {
    Diag(ErrorExpr->getLocStart(), diag::warn_pragma_unused_expected_localvar);
    for (unsigned i = 0; i < NumExprs; ++i)
      ((Expr*) Exprs[i])->Destroy(Context);    
    return;
  }
      
  // Otherwise, add the 'unused' attribute to each referenced declaration.
  for (unsigned i = 0; i < NumExprs; ++i) {
    DeclRefExpr *DR = (DeclRefExpr*) Exprs[i];
    DR->getDecl()->addAttr(::new (Context) UnusedAttr());
    DR->Destroy(Context);
  }
}