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Respect type alignment when choosing padding fields.

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Fixes ABI mismatch when e.g. padding a 28 byte union from a
20 byte member, where previously, an i64 would be emitted,
yielding a 32 byte LLVM struct size on ulong.alignof == 8
platforms.

Test case will follow on the 2.064 branch.
This commit is contained in:
David Nadlinger
2013-12-26 12:35:19 +01:00
parent 27ecc11915
commit f85d2a5a0a
4 changed files with 70 additions and 42 deletions
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ir/iraggr.cpp
+33 -21
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@@ -87,34 +87,50 @@ llvm::Constant * IrAggr::getDefaultInit()
//////////////////////////////////////////////////////////////////////////////
//////////////////////////////////////////////////////////////////////////////
static bool isAligned(llvm::Type* type, size_t offset) {
return gDataLayout->getABITypeAlignment(type) % offset == 0;
}
// helper function that adds zero bytes to a vector of constants
size_t add_zeros(llvm::SmallVectorImpl<llvm::Constant*>& constants, size_t diff)
size_t add_zeros(llvm::SmallVectorImpl<llvm::Constant*>& constants,
size_t startOffset, size_t endOffset)
{
size_t n = constants.size();
while (diff)
size_t const oldLength = constants.size();
llvm::Type* const eightByte = llvm::Type::getInt64Ty(gIR->context());
llvm::Type* const fourByte = llvm::Type::getInt32Ty(gIR->context());
llvm::Type* const twoByte = llvm::Type::getInt16Ty(gIR->context());
assert(startOffset <= endOffset);
size_t paddingLeft = endOffset - startOffset;
while (paddingLeft)
{
if (global.params.is64bit && diff % 8 == 0)
if (global.params.is64bit && paddingLeft >= 8 && isAligned(eightByte, startOffset))
{
constants.push_back(LLConstant::getNullValue(llvm::Type::getInt64Ty(gIR->context())));
diff -= 8;
constants.push_back(llvm::Constant::getNullValue(eightByte));
startOffset += 8;
}
else if (diff % 4 == 0)
else if (paddingLeft >= 4 && isAligned(fourByte, startOffset))
{
constants.push_back(LLConstant::getNullValue(llvm::Type::getInt32Ty(gIR->context())));
diff -= 4;
constants.push_back(llvm::Constant::getNullValue(fourByte));
startOffset += 4;
}
else if (diff % 2 == 0)
else if (paddingLeft >= 2 && isAligned(twoByte, startOffset))
{
constants.push_back(LLConstant::getNullValue(llvm::Type::getInt16Ty(gIR->context())));
diff -= 2;
constants.push_back(llvm::Constant::getNullValue(twoByte));
startOffset += 2;
}
else
{
constants.push_back(LLConstant::getNullValue(llvm::Type::getInt8Ty(gIR->context())));
diff -= 1;
constants.push_back(llvm::Constant::getNullValue(
llvm::Type::getInt8Ty(gIR->context())));
startOffset += 1;
}
paddingLeft = endOffset - startOffset;
}
return constants.size() - n;
return constants.size() - oldLength;
}
//////////////////////////////////////////////////////////////////////////////
@@ -263,9 +279,7 @@ llvm::Constant* IrAggr::createInitializerConstant(
const size_t structsize = type->size();
if (offset < structsize)
{
size_t diff = structsize - offset;
IF_LOG Logger::println("adding %zu bytes zero padding", diff);
add_zeros(constants, diff);
add_zeros(constants, offset, structsize);
}
// get initializer type
@@ -386,9 +400,7 @@ void IrAggr::addFieldInitializers(
// insert explicit padding?
if (alignedoffset < vd->offset)
{
size_t diff = vd->offset - alignedoffset;
IF_LOG Logger::println("adding %zu bytes zero padding", diff);
add_zeros(constants, diff);
add_zeros(constants, alignedoffset, vd->offset);
}
IF_LOG Logger::println("adding field %s", vd->toChars());