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Fix union layout and initialization

Browse source 
By refactoring IrAggr::addFieldInitializers() and making it use an
extended and refactored AggrTypeBuilder::addAggregate().

AggrTypeBuilder::addAggregate() can now optionally detect alias fields
in unions (same offset and LL type as a dominant union field) and add
those to the variable-to-GEP-index mapping.
These alias fields can then be indexed directly with a GEP instead of
resorting to casting the pointer and applying the byte offset.
This commit is contained in:
Martin 2016-10-21 03:32:58 +02:00
parent 2fa64b9662
commit e6537ba4dc
3 changed files with 118 additions and 231 deletions
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173
ir/iraggr.cpp
View file

@ -92,13 +92,6 @@ add_zeros(llvm::SmallVectorImpl<llvm::Constant *> &constants,
////////////////////////////////////////////////////////////////////////////// //////////////////////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////////////////////// //////////////////////////////////////////////////////////////////////////////
typedef std::pair<VarDeclaration *, llvm::Constant *> VarInitConst;
static bool struct_init_data_sort(const VarInitConst &a,
const VarInitConst &b) {
return (a.first && b.first) ? a.first->offset < b.first->offset : false;
}
// helper function that returns the static default initializer of a variable // helper function that returns the static default initializer of a variable
LLConstant *get_default_initializer(VarDeclaration *vd) { LLConstant *get_default_initializer(VarDeclaration *vd) {
if (vd->_init) { if (vd->_init) {
@ -171,9 +164,8 @@ IrAggr::createInitializerConstant(const VarInitMap &explicitInitializers,
// tail padding? // tail padding?
const size_t structsize = aggrdecl->size(Loc()); const size_t structsize = aggrdecl->size(Loc());
if (offset < structsize) { if (offset < structsize)
add_zeros(constants, offset, structsize); add_zeros(constants, offset, structsize);
}
// get initializer type // get initializer type
if (!initializerType || initializerType->isOpaque()) { if (!initializerType || initializerType->isOpaque()) {
@ -221,153 +213,44 @@ void IrAggr::addFieldInitializers(
bool newinsts = (cd == aggrdecl->isClassDeclaration()); bool newinsts = (cd == aggrdecl->isClassDeclaration());
size_t inter_idx = interfacesWithVtbls.size(); size_t inter_idx = interfacesWithVtbls.size();
offset = (offset + Target::ptrsize - 1) & ~(Target::ptrsize - 1);
for (auto bc : *cd->vtblInterfaces) { for (auto bc : *cd->vtblInterfaces) {
constants.push_back(getInterfaceVtbl(bc, newinsts, inter_idx)); constants.push_back(getInterfaceVtbl(bc, newinsts, inter_idx));
offset += Target::ptrsize; offset += Target::ptrsize;
inter_idx++; inter_idx++;
if (populateInterfacesWithVtbls) { if (populateInterfacesWithVtbls)
interfacesWithVtbls.push_back(bc); interfacesWithVtbls.push_back(bc);
} }
} }
} }
AggrTypeBuilder b(false, offset);
b.addAggregate(decl, &explicitInitializers, AggrTypeBuilder::Aliases::Skip);
offset = b.currentOffset();
const size_t baseLLFieldIndex = constants.size();
const size_t numNewLLFields = b.defaultTypes().size();
constants.resize(constants.size() + numNewLLFields, nullptr);
// add explicit and non-overlapping implicit initializers
for (const auto &pair : b.varGEPIndices()) {
const auto field = pair.first;
const size_t fieldIndex = pair.second;
const auto explicitIt = explicitInitializers.find(field);
llvm::Constant *init = (explicitIt != explicitInitializers.end()
? explicitIt->second
: get_default_initializer(field));
constants[baseLLFieldIndex + fieldIndex] =
FillSArrayDims(field->type, init);
} }
// Build up vector with one-to-one mapping to field indices. // zero out remaining padding fields
const size_t n = decl->fields.dim; for (size_t i = 0; i < numNewLLFields; i++) {
llvm::SmallVector<VarInitConst, 16> data(n); auto &init = constants[baseLLFieldIndex + i];
if (!init)
// Fill in explicit initializers. init = llvm::Constant::getNullValue(b.defaultTypes()[i]);
for (size_t i = 0; i < n; ++i) {
VarDeclaration *vd = decl->fields[i];
auto expl = explicitInitializers.find(vd);
if (expl != explicitInitializers.end()) {
const unsigned vd_begin = vd->offset;
const unsigned vd_end = vd_begin + vd->type->size();
// Make sure it doesn't overlap any prior initializers (needed for
// unions). This effectively initializes only the first member with an
// explicit initializer of a union.
// Only classes and structs can contain unions / overlapping fields.
if (type->ty == Tstruct || type->ty == Tclass) {
bool overlaps = false;
for (size_t j = 0; j < i; ++j) {
if (!data[j].first) {
continue;
}
const unsigned f_begin = decl->fields[j]->offset;
const unsigned f_end = f_begin + decl->fields[j]->type->size();
if (vd_begin >= f_end || vd_end <= f_begin) {
continue;
}
overlaps = true;
break;
}
if (overlaps)
continue;
}
data[i] = *expl;
}
}
// Fill in implicit initializers
for (size_t i = 0; i < n; i++) {
if (data[i].first) {
continue;
}
VarDeclaration *vd = decl->fields[i];
/* Skip void initializers for unions. DMD bug 3991:
union X
{
int a = void;
dchar b = 'a';
}
*/
// FIXME: decl->isUnionDeclaration() is always false, the FE lowers
// UnionDeclarations.
if (decl->isUnionDeclaration() && vd->_init &&
vd->_init->isVoidInitializer()) {
continue;
}
unsigned vd_begin = vd->offset;
unsigned vd_end = vd_begin + vd->type->size();
/* Skip zero size fields like zero-length static arrays, LDC issue 812:
class B {
ubyte[0] test;
}
*/
if (vd_begin == vd_end) {
continue;
}
// make sure it doesn't overlap any explicit initializers.
bool overlaps = false;
if (type->ty == Tstruct || type->ty == Tclass) {
// Only classes and structs can have overlapping fields.
for (size_t j = 0; j < n; ++j) {
if (i == j || !data[j].first) {
continue;
}
VarDeclaration *it = decl->fields[j];
unsigned f_begin = it->offset;
unsigned f_end = f_begin + it->type->size();
if (vd_begin >= f_end || vd_end <= f_begin) {
continue;
}
overlaps = true;
break;
}
}
// add if no overlap found
if (!overlaps) {
IF_LOG Logger::println("Implicit initializer: %s @+%u", vd->toChars(),
vd->offset);
LOG_SCOPE;
data[i].first = vd;
data[i].second = get_default_initializer(vd);
}
}
// Sort data array by offset.
// TODO: Figure out whether this is really necessary, fields should already
// be in offset order. Not having do do this would mean we could use a plain
// llvm::Constant* vector for initializers and avoid all the VarInitConst
// business.
std::sort(data.begin(), data.end(), struct_init_data_sort);
// build array of constants and make sure explicit zero padding is inserted
// when necessary.
for (size_t i = 0; i < n; i++) {
VarDeclaration *vd = data[i].first;
if (vd == nullptr) {
continue;
}
// Explicitly zero the padding as per TDPL §7.1.1. Otherwise, it would
// be left uninitialized by LLVM.
if (offset < vd->offset) {
add_zeros(constants, offset, vd->offset);
offset = vd->offset;
}
IF_LOG Logger::println("adding field %s", vd->toChars());
constants.push_back(FillSArrayDims(vd->type, data[i].second));
offset += getMemberSize(vd->type);
} }
} }

160
ir/irtypeaggr.cpp
View file

@ -42,7 +42,8 @@ bool var_offset_sort_cb(const VarDeclaration *v1, const VarDeclaration *v2) {
return v1 && !v2; return v1 && !v2;
} }
AggrTypeBuilder::AggrTypeBuilder(bool packed) : m_packed(packed) { AggrTypeBuilder::AggrTypeBuilder(bool packed, unsigned offset)
: m_packed(packed), m_offset(offset) {
m_defaultTypes.reserve(32); m_defaultTypes.reserve(32);
} }
@ -53,110 +54,100 @@ void AggrTypeBuilder::addType(llvm::Type *type, unsigned size) {
} }
void AggrTypeBuilder::addAggregate(AggregateDeclaration *ad) { void AggrTypeBuilder::addAggregate(AggregateDeclaration *ad) {
// mirror the ad->fields array but only fill in contributors addAggregate(ad, nullptr, Aliases::AddToVarGEPIndices);
}
namespace {
enum FieldPriority {
FP_ExplicitVoid = 0, // lowest priority: fields with explicit void initializer
FP_Default = 1, // default initializer
FP_Explicit = 2, // explicit non-void initializer
FP_Value = 3, // highest priority: values (for literals)
};
FieldPriority prioritize(VarDeclaration *field,
const AggrTypeBuilder::VarInitMap *explicitInits) {
if (explicitInits && explicitInits->find(field) != explicitInits->end())
return FP_Value;
if (auto init = field->_init)
return !init->isVoidInitializer() ? FP_Explicit : FP_ExplicitVoid;
return FP_Default;
}
}
void AggrTypeBuilder::addAggregate(
AggregateDeclaration *ad, const AggrTypeBuilder::VarInitMap *explicitInits,
AggrTypeBuilder::Aliases aliases) {
const size_t n = ad->fields.dim; const size_t n = ad->fields.dim;
if (n == 0)
return;
// prioritize overlapping fields
LLSmallVector<FieldPriority, 16> priorities;
priorities.reserve(n);
for (auto f : ad->fields) {
priorities.push_back(prioritize(f, explicitInits));
IF_LOG Logger::println("Field priority for %s: %d", f->toChars(),
priorities.back());
}
// mirror the ad->fields array but only fill in contributors
LLSmallVector<VarDeclaration *, 16> data(n, nullptr); LLSmallVector<VarDeclaration *, 16> data(n, nullptr);
unsigned int errors = global.errors; // list of pairs: alias => actual field (same offset, same LL type)
LLSmallVector<std::pair<VarDeclaration *, VarDeclaration *>, 16> aliasPairs;
// first fill in the fields with explicit initializers // one pass per priority in descending order
const auto minMaxPriority =
std::minmax_element(priorities.begin(), priorities.end());
for (int p = *minMaxPriority.second; p >= *minMaxPriority.first; p--) {
// iterate over fields of that priority, in declaration order
for (size_t index = 0; index < n; ++index) { for (size_t index = 0; index < n; ++index) {
if (priorities[index] != p)
continue;
VarDeclaration *field = ad->fields[index]; VarDeclaration *field = ad->fields[index];
const size_t f_begin = field->offset;
const size_t f_end = f_begin + field->type->size();
// _init is !null for explicit inits // skip empty fields
if (field->_init != nullptr && !field->_init->isVoidInitializer()) { if (f_begin == f_end)
IF_LOG Logger::println("adding explicit initializer for struct field %s",
field->toChars());
size_t f_size = field->type->size();
size_t f_begin = field->offset;
size_t f_end = f_begin + f_size;
if (f_size == 0) {
continue; continue;
}
data[index] = field; // check for overlapping existing fields
// make sure there is no overlap
for (size_t i = 0; i < index; i++) {
if (data[i] != nullptr) {
VarDeclaration *vd = data[i];
size_t v_begin = vd->offset;
size_t v_end = v_begin + vd->type->size();
if (v_begin >= f_end || v_end <= f_begin) {
continue;
}
ad->error(vd->loc, "has overlapping initialization for %s and %s",
field->toChars(), vd->toChars());
}
}
}
}
if (errors != global.errors) {
// There was an overlapping initialization.
// Return if errors are gagged otherwise abort.
if (global.gag) {
return;
}
fatal();
}
// fill in default initializers
for (size_t index = 0; index < n; ++index) {
if (data[index]) {
continue;
}
VarDeclaration *field = ad->fields[index];
size_t f_size = field->type->size();
size_t f_begin = field->offset;
size_t f_end = f_begin + f_size;
if (f_size == 0) {
continue;
}
// make sure it doesn't overlap anything explicit
bool overlaps = false; bool overlaps = false;
for (size_t i = 0; i < n; i++) { for (const auto vd : data) {
if (data[i]) { if (!vd)
size_t v_begin = data[i]->offset;
size_t v_end = v_begin + data[i]->type->size();
if (v_begin >= f_end || v_end <= f_begin) {
continue; continue;
}
const size_t v_begin = vd->offset;
const size_t v_end = v_begin + vd->type->size();
if (v_begin < f_end && v_end > f_begin) {
if (aliases == Aliases::AddToVarGEPIndices && v_begin == f_begin &&
DtoMemType(vd->type) == DtoMemType(field->type)) {
aliasPairs.push_back(std::make_pair(field, vd));
}
overlaps = true; overlaps = true;
break; break;
} }
} }
// if no overlap was found, add the default initializer if (!overlaps)
if (!overlaps) {
IF_LOG Logger::println("adding default initializer for struct field %s",
field->toChars());
data[index] = field; data[index] = field;
} }
} }
// // Now we can build a list of LLVM types for the actual LL fields.
// ok. now we can build a list of llvm types. and make sure zeros are inserted // Make sure to zero out any padding and set the GEP indices for the directly
// if necessary. // indexable variables.
//
// first we sort the list by offset // first we sort the list by offset
std::sort(data.begin(), data.end(), var_offset_sort_cb); std::sort(data.begin(), data.end(), var_offset_sort_cb);
// add types to list for (const auto vd : data) {
for (size_t i = 0; i < n; i++) { if (!vd)
VarDeclaration *vd = data[i];
if (vd == nullptr) {
continue; continue;
}
assert(vd->offset >= m_offset && "Variable overlaps previous field."); assert(vd->offset >= m_offset && "Variable overlaps previous field.");
@ -175,6 +166,13 @@ void AggrTypeBuilder::addAggregate(AggregateDeclaration *ad) {
// set the field index // set the field index
m_varGEPIndices[vd] = m_fieldIndex; m_varGEPIndices[vd] = m_fieldIndex;
// let any aliases reuse this field/GEP index
for (const auto &pair : aliasPairs) {
if (pair.second == vd)
m_varGEPIndices[pair.first] = m_fieldIndex;
}
++m_fieldIndex; ++m_fieldIndex;
} }
} }
@ -190,11 +188,9 @@ void AggrTypeBuilder::alignCurrentOffset(unsigned alignment) {
} }
void AggrTypeBuilder::addTailPadding(unsigned aggregateSize) { void AggrTypeBuilder::addTailPadding(unsigned aggregateSize) {
// tail padding? if (m_offset < aggregateSize)
if (m_offset < aggregateSize) {
add_zeros(m_defaultTypes, m_offset, aggregateSize); add_zeros(m_defaultTypes, m_offset, aggregateSize);
} }
}
////////////////////////////////////////////////////////////////////////////// //////////////////////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////////////////////// //////////////////////////////////////////////////////////////////////////////

14
ir/irtypeaggr.h
View file

@ -28,15 +28,23 @@ using VarGEPIndices = std::map<VarDeclaration *, unsigned>;
class AggrTypeBuilder { class AggrTypeBuilder {
public: public:
explicit AggrTypeBuilder(bool packed); using VarInitMap = std::map<VarDeclaration *, llvm::Constant *>;
enum class Aliases { Skip, AddToVarGEPIndices };
explicit AggrTypeBuilder(bool packed, unsigned offset = 0);
void addType(llvm::Type *type, unsigned size); void addType(llvm::Type *type, unsigned size);
void addAggregate(AggregateDeclaration *ad); void addAggregate(AggregateDeclaration *ad);
void addAggregate(AggregateDeclaration *ad, const VarInitMap *explicitInits,
Aliases aliases);
void alignCurrentOffset(unsigned alignment); void alignCurrentOffset(unsigned alignment);
void addTailPadding(unsigned aggregateSize); void addTailPadding(unsigned aggregateSize);
unsigned currentFieldIndex() const { return m_fieldIndex; } unsigned currentFieldIndex() const { return m_fieldIndex; }
std::vector<llvm::Type *> defaultTypes() const { return m_defaultTypes; } const std::vector<llvm::Type *> &defaultTypes() const {
VarGEPIndices varGEPIndices() const { return m_varGEPIndices; } return m_defaultTypes;
}
const VarGEPIndices &varGEPIndices() const { return m_varGEPIndices; }
unsigned overallAlignment() const { return m_overallAlignment; } unsigned overallAlignment() const { return m_overallAlignment; }
unsigned currentOffset() const { return m_offset; }
protected: protected:
std::vector<llvm::Type *> m_defaultTypes; std::vector<llvm::Type *> m_defaultTypes;