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llvm-project/clang/lib/CodeGen/CGExprConstant.cpp

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//===--- 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/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 ConstExprEmitter :
public StmtVisitor<ConstExprEmitter, llvm::Constant*> {
CodeGenModule &CGM;
CodeGenFunction *CGF;
llvm::LLVMContext &VMContext;
public:
ConstExprEmitter(CodeGenModule &cgm, CodeGenFunction *cgf)
: CGM(cgm), CGF(cgf), VMContext(cgm.getLLVMContext()) {
}
//===--------------------------------------------------------------------===//
// Visitor Methods
//===--------------------------------------------------------------------===//
llvm::Constant *VisitStmt(Stmt *S) {
return 0;
}
llvm::Constant *VisitParenExpr(ParenExpr *PE) {
return Visit(PE->getSubExpr());
}
llvm::Constant *VisitCompoundLiteralExpr(CompoundLiteralExpr *E) {
return Visit(E->getInitializer());
}
llvm::Constant *VisitCastExpr(CastExpr* E) {
// GCC cast to union extension
if (E->getType()->isUnionType()) {
const llvm::Type *Ty = ConvertType(E->getType());
Expr *SubExpr = E->getSubExpr();
return EmitUnion(CGM.EmitConstantExpr(SubExpr, SubExpr->getType(), CGF),
Ty);
}
// Explicit and implicit no-op casts
QualType Ty = E->getType(), SubTy = E->getSubExpr()->getType();
if (CGM.getContext().hasSameUnqualifiedType(Ty, SubTy)) {
return Visit(E->getSubExpr());
}
return 0;
}
llvm::Constant *VisitCXXDefaultArgExpr(CXXDefaultArgExpr *DAE) {
return Visit(DAE->getExpr());
}
llvm::Constant *EmitArrayInitialization(InitListExpr *ILE) {
std::vector<llvm::Constant*> Elts;
const llvm::ArrayType *AType =
cast<llvm::ArrayType>(ConvertType(ILE->getType()));
unsigned NumInitElements = ILE->getNumInits();
// FIXME: Check for wide strings
// FIXME: Check for NumInitElements exactly equal to 1??
if (NumInitElements > 0 &&
(isa<StringLiteral>(ILE->getInit(0)) ||
isa<ObjCEncodeExpr>(ILE->getInit(0))) &&
ILE->getType()->getArrayElementTypeNoTypeQual()->isCharType())
return Visit(ILE->getInit(0));
const llvm::Type *ElemTy = AType->getElementType();
unsigned NumElements = AType->getNumElements();
// Initialising an array requires us to automatically
// initialise any elements that have not been initialised explicitly
unsigned NumInitableElts = std::min(NumInitElements, NumElements);
// Copy initializer elements.
unsigned i = 0;
bool RewriteType = false;
for (; i < NumInitableElts; ++i) {
Expr *Init = ILE->getInit(i);
llvm::Constant *C = CGM.EmitConstantExpr(Init, Init->getType(), CGF);
if (!C)
return 0;
RewriteType |= (C->getType() != ElemTy);
Elts.push_back(C);
}
// Initialize remaining array elements.
// FIXME: This doesn't handle member pointers correctly!
for (; i < NumElements; ++i)
Elts.push_back(VMContext.getNullValue(ElemTy));
if (RewriteType) {
// FIXME: Try to avoid packing the array
std::vector<const llvm::Type*> Types;
for (unsigned i = 0; i < Elts.size(); ++i)
Types.push_back(Elts[i]->getType());
const llvm::StructType *SType = VMContext.getStructType(Types, true);
return VMContext.getConstantStruct(SType, Elts);
}
return VMContext.getConstantArray(AType, Elts);
}
void InsertBitfieldIntoStruct(std::vector<llvm::Constant*>& Elts,
FieldDecl* Field, Expr* E) {
// Calculate the value to insert
llvm::Constant *C = CGM.EmitConstantExpr(E, Field->getType(), CGF);
if (!C)
return;
llvm::ConstantInt *CI = dyn_cast<llvm::ConstantInt>(C);
if (!CI) {
CGM.ErrorUnsupported(E, "bitfield initialization");
return;
}
llvm::APInt V = CI->getValue();
// Calculate information about the relevant field
const llvm::Type* Ty = CI->getType();
const llvm::TargetData &TD = CGM.getTypes().getTargetData();
unsigned size = TD.getTypeAllocSizeInBits(Ty);
unsigned fieldOffset = CGM.getTypes().getLLVMFieldNo(Field) * size;
CodeGenTypes::BitFieldInfo bitFieldInfo =
CGM.getTypes().getBitFieldInfo(Field);
fieldOffset += bitFieldInfo.Begin;
// Find where to start the insertion
// FIXME: This is O(n^2) in the number of bit-fields!
// FIXME: This won't work if the struct isn't completely packed!
unsigned offset = 0, i = 0;
while (offset < (fieldOffset & -8))
offset += TD.getTypeAllocSizeInBits(Elts[i++]->getType());
// Advance over 0 sized elements (must terminate in bounds since
// the bitfield must have a size).
while (TD.getTypeAllocSizeInBits(Elts[i]->getType()) == 0)
++i;
// Promote the size of V 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 (bitFieldInfo.Size > V.getBitWidth())
V.zext(bitFieldInfo.Size);
// Insert the bits into the struct
// FIXME: This algorthm is only correct on X86!
// FIXME: THis algorthm assumes bit-fields only have byte-size elements!
unsigned bitsToInsert = bitFieldInfo.Size;
unsigned curBits = std::min(8 - (fieldOffset & 7), bitsToInsert);
unsigned byte = V.getLoBits(curBits).getZExtValue() << (fieldOffset & 7);
do {
llvm::Constant* byteC =
VMContext.getConstantInt(llvm::Type::Int8Ty, byte);
Elts[i] = VMContext.getConstantExprOr(Elts[i], byteC);
++i;
V = V.lshr(curBits);
bitsToInsert -= curBits;
if (!bitsToInsert)
break;
curBits = bitsToInsert > 8 ? 8 : bitsToInsert;
byte = V.getLoBits(curBits).getZExtValue();
} while (true);
}
llvm::Constant *EmitStructInitialization(InitListExpr *ILE) {
const llvm::StructType *SType =
cast<llvm::StructType>(ConvertType(ILE->getType()));
RecordDecl *RD = ILE->getType()->getAsRecordType()->getDecl();
std::vector<llvm::Constant*> Elts;
// Initialize the whole structure to zero.
// FIXME: This doesn't handle member pointers correctly!
for (unsigned i = 0; i < SType->getNumElements(); ++i) {
const llvm::Type *FieldTy = SType->getElementType(i);
Elts.push_back(VMContext.getNullValue(FieldTy));
}
// Copy initializer elements. Skip padding fields.
unsigned EltNo = 0; // Element no in ILE
bool RewriteType = false;
for (RecordDecl::field_iterator Field = RD->field_begin(),
FieldEnd = RD->field_end();
EltNo < ILE->getNumInits() && Field != FieldEnd; ++Field) {
if (Field->isBitField()) {
if (!Field->getIdentifier())
continue;
InsertBitfieldIntoStruct(Elts, *Field, ILE->getInit(EltNo));
} else {
unsigned FieldNo = CGM.getTypes().getLLVMFieldNo(*Field);
llvm::Constant *C = CGM.EmitConstantExpr(ILE->getInit(EltNo),
Field->getType(), CGF);
if (!C) return 0;
RewriteType |= (C->getType() != Elts[FieldNo]->getType());
Elts[FieldNo] = C;
}
EltNo++;
}
if (RewriteType) {
// FIXME: Make this work for non-packed structs
assert(SType->isPacked() && "Cannot recreate unpacked structs");
std::vector<const llvm::Type*> Types;
for (unsigned i = 0; i < Elts.size(); ++i)
Types.push_back(Elts[i]->getType());
SType = VMContext.getStructType(Types, true);
}
return VMContext.getConstantStruct(SType, Elts);
}
llvm::Constant *EmitUnion(llvm::Constant *C, const llvm::Type *Ty) {
if (!C)
return 0;
// Build a struct with the union sub-element as the first member,
// and padded to the appropriate size
std::vector<llvm::Constant*> Elts;
std::vector<const llvm::Type*> Types;
Elts.push_back(C);
Types.push_back(C->getType());
unsigned CurSize = CGM.getTargetData().getTypeAllocSize(C->getType());
unsigned TotalSize = CGM.getTargetData().getTypeAllocSize(Ty);
while (CurSize < TotalSize) {
Elts.push_back(VMContext.getNullValue(llvm::Type::Int8Ty));
Types.push_back(llvm::Type::Int8Ty);
CurSize++;
}
// This always generates a packed struct
// FIXME: Try to generate an unpacked struct when we can
llvm::StructType* STy = VMContext.getStructType(Types, true);
return VMContext.getConstantStruct(STy, Elts);
}
llvm::Constant *EmitUnionInitialization(InitListExpr *ILE) {
const llvm::Type *Ty = ConvertType(ILE->getType());
FieldDecl* curField = ILE->getInitializedFieldInUnion();
if (!curField) {
// There's no field to initialize, so value-initialize the union.
#ifndef NDEBUG
// Make sure that it's really an empty and not a failure of
// semantic analysis.
RecordDecl *RD = ILE->getType()->getAsRecordType()->getDecl();
for (RecordDecl::field_iterator Field = RD->field_begin(),
FieldEnd = RD->field_end();
Field != FieldEnd; ++Field)
assert(Field->isUnnamedBitfield() && "Only unnamed bitfields allowed");
#endif
return VMContext.getNullValue(Ty);
}
if (curField->isBitField()) {
// Create a dummy struct for bit-field insertion
unsigned NumElts = CGM.getTargetData().getTypeAllocSize(Ty);
llvm::Constant* NV =
VMContext.getNullValue(llvm::Type::Int8Ty);
std::vector<llvm::Constant*> Elts(NumElts, NV);
InsertBitfieldIntoStruct(Elts, curField, ILE->getInit(0));
const llvm::ArrayType *RetTy =
VMContext.getArrayType(NV->getType(), NumElts);
return VMContext.getConstantArray(RetTy, Elts);
}
llvm::Constant *InitElem;
if (ILE->getNumInits() > 0) {
Expr *Init = ILE->getInit(0);
InitElem = CGM.EmitConstantExpr(Init, Init->getType(), CGF);
} else {
InitElem = CGM.EmitNullConstant(curField->getType());
}
return EmitUnion(InitElem, Ty);
}
llvm::Constant *EmitVectorInitialization(InitListExpr *ILE) {
const llvm::VectorType *VType =
cast<llvm::VectorType>(ConvertType(ILE->getType()));
const llvm::Type *ElemTy = VType->getElementType();
std::vector<llvm::Constant*> Elts;
unsigned NumElements = VType->getNumElements();
unsigned NumInitElements = ILE->getNumInits();
unsigned NumInitableElts = std::min(NumInitElements, NumElements);
// Copy initializer elements.
unsigned i = 0;
for (; i < NumInitableElts; ++i) {
Expr *Init = ILE->getInit(i);
llvm::Constant *C = CGM.EmitConstantExpr(Init, Init->getType(), CGF);
if (!C)
return 0;
Elts.push_back(C);
}
for (; i < NumElements; ++i)
Elts.push_back(VMContext.getNullValue(ElemTy));
return VMContext.getConstantVector(VType, Elts);
}
llvm::Constant *VisitImplicitValueInitExpr(ImplicitValueInitExpr* E) {
return CGM.EmitNullConstant(E->getType());
}
llvm::Constant *VisitInitListExpr(InitListExpr *ILE) {
if (ILE->getType()->isScalarType()) {
// We have a scalar in braces. Just use the first element.
if (ILE->getNumInits() > 0) {
Expr *Init = ILE->getInit(0);
return CGM.EmitConstantExpr(Init, Init->getType(), CGF);
}
return CGM.EmitNullConstant(ILE->getType());
}
if (ILE->getType()->isArrayType())
return EmitArrayInitialization(ILE);
if (ILE->getType()->isStructureType())
return EmitStructInitialization(ILE);
if (ILE->getType()->isUnionType())
return EmitUnionInitialization(ILE);
if (ILE->getType()->isVectorType())
return EmitVectorInitialization(ILE);
assert(0 && "Unable to handle InitListExpr");
// Get rid of control reaches end of void function warning.
// Not reached.
return 0;
}
llvm::Constant *VisitStringLiteral(StringLiteral *E) {
assert(!E->getType()->isPointerType() && "Strings are always arrays");
// This must be a string initializing an array in a static initializer.
// Don't emit it as the address of the string, emit the string data itself
// as an inline array.
return VMContext.getConstantArray(CGM.GetStringForStringLiteral(E), false);
}
llvm::Constant *VisitObjCEncodeExpr(ObjCEncodeExpr *E) {
// This must be an @encode initializing an array in a static initializer.
// Don't emit it as the address of the string, emit the string data itself
// as an inline array.
std::string Str;
CGM.getContext().getObjCEncodingForType(E->getEncodedType(), Str);
const ConstantArrayType *CAT = cast<ConstantArrayType>(E->getType());
// Resize the string to the right size, adding zeros at the end, or
// truncating as needed.
Str.resize(CAT->getSize().getZExtValue(), '\0');
return VMContext.getConstantArray(Str, false);
}
llvm::Constant *VisitUnaryExtension(const UnaryOperator *E) {
return Visit(E->getSubExpr());
}
// Utility methods
const llvm::Type *ConvertType(QualType T) {
return CGM.getTypes().ConvertType(T);
}
public:
llvm::Constant *EmitLValue(Expr *E) {
switch (E->getStmtClass()) {
default: break;
case Expr::CompoundLiteralExprClass: {
// Note that due to the nature of compound literals, this is guaranteed
// to be the only use of the variable, so we just generate it here.
CompoundLiteralExpr *CLE = cast<CompoundLiteralExpr>(E);
llvm::Constant* C = Visit(CLE->getInitializer());
// FIXME: "Leaked" on failure.
if (C)
C = new llvm::GlobalVariable(CGM.getModule(), C->getType(),
E->getType().isConstQualified(),
llvm::GlobalValue::InternalLinkage,
C, ".compoundliteral");
return C;
}
case Expr::DeclRefExprClass:
case Expr::QualifiedDeclRefExprClass: {
NamedDecl *Decl = cast<DeclRefExpr>(E)->getDecl();
if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(Decl))
return CGM.GetAddrOfFunction(GlobalDecl(FD));
if (const VarDecl* VD = dyn_cast<VarDecl>(Decl)) {
// We can never refer to a variable with local storage.
if (!VD->hasLocalStorage()) {
if (VD->isFileVarDecl() || VD->hasExternalStorage())
return CGM.GetAddrOfGlobalVar(VD);
else if (VD->isBlockVarDecl()) {
assert(CGF && "Can't access static local vars without CGF");
return CGF->GetAddrOfStaticLocalVar(VD);
}
}
}
break;
}
case Expr::StringLiteralClass:
return CGM.GetAddrOfConstantStringFromLiteral(cast<StringLiteral>(E));
case Expr::ObjCEncodeExprClass:
return CGM.GetAddrOfConstantStringFromObjCEncode(cast<ObjCEncodeExpr>(E));
case Expr::ObjCStringLiteralClass: {
ObjCStringLiteral* SL = cast<ObjCStringLiteral>(E);
llvm::Constant *C = CGM.getObjCRuntime().GenerateConstantString(SL);
return VMContext.getConstantExprBitCast(C, ConvertType(E->getType()));
}
case Expr::PredefinedExprClass: {
// __func__/__FUNCTION__ -> "". __PRETTY_FUNCTION__ -> "top level".
std::string Str;
if (cast<PredefinedExpr>(E)->getIdentType() ==
PredefinedExpr::PrettyFunction)
Str = "top level";
return CGM.GetAddrOfConstantCString(Str, ".tmp");
}
case Expr::AddrLabelExprClass: {
assert(CGF && "Invalid address of label expression outside function.");
unsigned id = CGF->GetIDForAddrOfLabel(cast<AddrLabelExpr>(E)->getLabel());
llvm::Constant *C = VMContext.getConstantInt(llvm::Type::Int32Ty, id);
return VMContext.getConstantExprIntToPtr(C, ConvertType(E->getType()));
}
case Expr::CallExprClass: {
CallExpr* CE = cast<CallExpr>(E);
if (CE->isBuiltinCall(CGM.getContext()) !=
Builtin::BI__builtin___CFStringMakeConstantString)
break;
const Expr *Arg = CE->getArg(0)->IgnoreParenCasts();
const StringLiteral *Literal = cast<StringLiteral>(Arg);
// FIXME: need to deal with UCN conversion issues.
return CGM.GetAddrOfConstantCFString(Literal);
}
case Expr::BlockExprClass: {
std::string FunctionName;
if (CGF)
FunctionName = CGF->CurFn->getName();
else
FunctionName = "global";
return CGM.GetAddrOfGlobalBlock(cast<BlockExpr>(E), FunctionName.c_str());
}
}
return 0;
}
};
} // end anonymous namespace.
llvm::Constant *CodeGenModule::EmitConstantExpr(const Expr *E,
QualType DestType,
CodeGenFunction *CGF) {
Expr::EvalResult Result;
bool Success = false;
if (DestType->isReferenceType())
Success = E->EvaluateAsLValue(Result, Context);
else
Success = E->Evaluate(Result, Context);
if (Success) {
assert(!Result.HasSideEffects &&
"Constant expr should not have any side effects!");
switch (Result.Val.getKind()) {
case APValue::Uninitialized:
assert(0 && "Constant expressions should be initialized.");
return 0;
case APValue::LValue: {
const llvm::Type *DestTy = getTypes().ConvertTypeForMem(DestType);
llvm::Constant *Offset =
VMContext.getConstantInt(llvm::Type::Int64Ty,
Result.Val.getLValueOffset());
llvm::Constant *C;
if (const Expr *LVBase = Result.Val.getLValueBase()) {
C = ConstExprEmitter(*this, CGF).EmitLValue(const_cast<Expr*>(LVBase));
// Apply offset if necessary.
if (!Offset->isNullValue()) {
const llvm::Type *Type =
VMContext.getPointerTypeUnqual(llvm::Type::Int8Ty);
llvm::Constant *Casted = VMContext.getConstantExprBitCast(C, Type);
Casted = VMContext.getConstantExprGetElementPtr(Casted, &Offset, 1);
C = VMContext.getConstantExprBitCast(Casted, C->getType());
}
// Convert to the appropriate type; this could be an lvalue for
// an integer.
if (isa<llvm::PointerType>(DestTy))
return VMContext.getConstantExprBitCast(C, DestTy);
return VMContext.getConstantExprPtrToInt(C, DestTy);
} else {
C = Offset;
// Convert to the appropriate type; this could be an lvalue for
// an integer.
if (isa<llvm::PointerType>(DestTy))
return VMContext.getConstantExprIntToPtr(C, DestTy);
// If the types don't match this should only be a truncate.
if (C->getType() != DestTy)
return VMContext.getConstantExprTrunc(C, DestTy);
return C;
}
}
case APValue::Int: {
llvm::Constant *C = VMContext.getConstantInt(Result.Val.getInt());
if (C->getType() == llvm::Type::Int1Ty) {
const llvm::Type *BoolTy = getTypes().ConvertTypeForMem(E->getType());
C = VMContext.getConstantExprZExt(C, BoolTy);
}
return C;
}
case APValue::ComplexInt: {
llvm::Constant *Complex[2];
Complex[0] = VMContext.getConstantInt(Result.Val.getComplexIntReal());
Complex[1] = VMContext.getConstantInt(Result.Val.getComplexIntImag());
return VMContext.getConstantStruct(Complex, 2);
}
case APValue::Float:
return VMContext.getConstantFP(Result.Val.getFloat());
case APValue::ComplexFloat: {
llvm::Constant *Complex[2];
Complex[0] = VMContext.getConstantFP(Result.Val.getComplexFloatReal());
Complex[1] = VMContext.getConstantFP(Result.Val.getComplexFloatImag());
return VMContext.getConstantStruct(Complex, 2);
}
case APValue::Vector: {
llvm::SmallVector<llvm::Constant *, 4> Inits;
unsigned NumElts = Result.Val.getVectorLength();
for (unsigned i = 0; i != NumElts; ++i) {
APValue &Elt = Result.Val.getVectorElt(i);
if (Elt.isInt())
Inits.push_back(VMContext.getConstantInt(Elt.getInt()));
else
Inits.push_back(VMContext.getConstantFP(Elt.getFloat()));
}
return VMContext.getConstantVector(&Inits[0], Inits.size());
}
}
}
llvm::Constant* C = ConstExprEmitter(*this, CGF).Visit(const_cast<Expr*>(E));
if (C && C->getType() == llvm::Type::Int1Ty) {
const llvm::Type *BoolTy = getTypes().ConvertTypeForMem(E->getType());
C = VMContext.getConstantExprZExt(C, BoolTy);
}
return C;
}
llvm::Constant *CodeGenModule::EmitNullConstant(QualType T) {
// Always return an LLVM null constant for now; this will change when we
// get support for IRGen of member pointers.
return getLLVMContext().getNullValue(getTypes().ConvertType(T));
}
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