averello/swift-mirror
1
0
Fork 0
mirror of https://github.com/apple/swift.git synced 2025-12-14 20:36:38 +01:00
Code Issues Packages Projects Releases Wiki Activity

Count tail-padding in the size of imported C types.

Browse Source 
This allows us to freely pass the address of a variable of such
types to a C function without worrying about it overwriting other
things if e.g. it memcpy's sizeof(T) bytes and thus clobbers the
otherwise-non-existent tail padding.

There are ways to get this optimization back, but they require
things like materializing to a temporary instead of passing the
address directly.  We haven't done that work yet, so we don't
get to take advantage of it.

rdar://26828018
This commit is contained in:
John McCall
2016-08-02 13:26:11 -07:00
parent 212ffadf5e
commit b51a69f29f
4 changed files with 33 additions and 34 deletions
Download Patch File Download Diff File Expand all files Collapse all files

23
lib/IRGen/GenStruct.cpp
View File

@@ -579,7 +579,6 @@ class ClangRecordLowering {
const clang::ASTContext &ClangContext;
const clang::ASTRecordLayout &ClangLayout;
const Size TotalStride;
Size TotalSize;
const Alignment TotalAlignment;
SpareBitVector SpareBits;
@@ -595,9 +594,8 @@ public:
ClangDecl(clangDecl), ClangContext(clangDecl->getASTContext()),
ClangLayout(ClangContext.getASTRecordLayout(clangDecl)),
TotalStride(Size(ClangLayout.getSize().getQuantity())),
TotalSize(TotalStride),
TotalAlignment(Alignment(ClangLayout.getAlignment().getQuantity())) {
SpareBits.reserve(TotalSize.getValue() * 8);
SpareBits.reserve(TotalStride.getValue() * 8);
}
void collectRecordFields() {
@@ -606,17 +604,12 @@ public:
} else {
collectStructFields();
}
// Lots of layout will get screwed up if our structure claims more
// storage than we allocated to it.
assert(NextOffset == TotalSize && NextOffset <= TotalStride);
assert(TotalSize.roundUpToAlignment(TotalAlignment) == TotalStride);
}
const TypeInfo *createTypeInfo(llvm::StructType *llvmType) {
llvmType->setBody(LLVMFields, /*packed*/ true);
return ClangRecordTypeInfo::create(FieldInfos, NextExplosionIndex,
llvmType, TotalSize,
llvmType, TotalStride,
std::move(SpareBits), TotalAlignment,
ClangDecl);
}
@@ -624,7 +617,7 @@ public:
private:
/// Collect all the fields of a union.
void collectUnionFields() {
addOpaqueField(Size(0), TotalSize);
addOpaqueField(Size(0), TotalStride);
}
static bool isImportOfClangField(VarDecl *swiftField,
@@ -689,8 +682,14 @@ private:
assert(sfi == sfe && "more Swift fields than there were Clang fields?");
// Treat this as the end of the value size.
TotalSize = NextOffset;
// We never take advantage of tail padding, because that would prevent
// us from passing the address of the object off to C, which is a pretty
// likely scenario for imported C types.
assert(NextOffset <= TotalStride);
assert(SpareBits.size() <= TotalStride.getValueInBits());
if (NextOffset < TotalStride) {
addPaddingField(TotalStride);
}
}
/// Place the next struct field at its appropriate offset.