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When an externally-supplied record layout has a size that clearly 

doesn't include padding up to the alignment of the record, take this
as a cue that the alignment of the record should (conservatively) be
set to 1. This is similar to other the other cues we use to determine
that the record has a lower alignment, e.g., that the
externally-supplied layout places fields at lower offsets than we
would. Fixes <rdar://problem/12582052>; test case in LLDB.

llvm-svn: 166824
This commit is contained in:
Douglas Gregor 2012-10-26 22:31:14 +00:00
parent 9dd2e0872e
commit 1423a5cfd7
2 changed files with 47 additions and 16 deletions
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48
clang/lib/AST/RecordLayoutBuilder.cpp
View File

@ -1557,6 +1557,13 @@ CharUnits RecordLayoutBuilder::LayoutBase(const BaseSubobjectInfo *Base) {
bool Allowed = EmptySubobjects->CanPlaceBaseAtOffset(Base, Offset);
(void)Allowed;
assert(Allowed && "Base subobject externally placed at overlapping offset");
if (InferAlignment && Offset < getDataSize().RoundUpToAlignment(BaseAlign)){
// The externally-supplied base offset is before the base offset we
// computed. Assume that the structure is packed.
Alignment = CharUnits::One();
InferAlignment = false;
}
}
if (!Base->Class->isEmpty()) {
@ -1616,7 +1623,6 @@ void RecordLayoutBuilder::InitializeLayout(const Decl *D) {
if (ExternalLayout) {
if (ExternalAlign > 0) {
Alignment = Context.toCharUnitsFromBits(ExternalAlign);
UnpackedAlignment = Alignment;
} else {
// The external source didn't have alignment information; infer it.
InferAlignment = true;
@ -2166,11 +2172,6 @@ void RecordLayoutBuilder::LayoutField(const FieldDecl *D) {
}
void RecordLayoutBuilder::FinishLayout(const NamedDecl *D) {
if (ExternalLayout) {
setSize(ExternalSize);
return;
}
// In C++, records cannot be of size 0.
if (Context.getLangOpts().CPlusPlus && getSizeInBits() == 0) {
if (const CXXRecordDecl *RD = dyn_cast<CXXRecordDecl>(D)) {
@ -2184,20 +2185,37 @@ void RecordLayoutBuilder::FinishLayout(const NamedDecl *D) {
setSize(CharUnits::One());
}
// Finally, round the size of the record up to the alignment of the
// record itself.
uint64_t UnpaddedSize = getSizeInBits() - UnfilledBitsInLastByte;
uint64_t UnpackedSizeInBits =
llvm::RoundUpToAlignment(getSizeInBits(),
Context.toBits(UnpackedAlignment));
CharUnits UnpackedSize = Context.toCharUnitsFromBits(UnpackedSizeInBits);
uint64_t RoundedSize
= llvm::RoundUpToAlignment(getSizeInBits(), Context.toBits(Alignment));
if (ExternalLayout) {
// If we're inferring alignment, and the external size is smaller than
// our size after we've rounded up to alignment, conservatively set the
// alignment to 1.
if (InferAlignment && ExternalSize < RoundedSize) {
Alignment = CharUnits::One();
InferAlignment = false;
}
setSize(ExternalSize);
return;
}
// MSVC doesn't round up to the alignment of the record with virtual bases.
if (const CXXRecordDecl *RD = dyn_cast<CXXRecordDecl>(D)) {
if (isMicrosoftCXXABI() && RD->getNumVBases())
return;
}
// Finally, round the size of the record up to the alignment of the
// record itself.
uint64_t UnpaddedSize = getSizeInBits() - UnfilledBitsInLastByte;
uint64_t UnpackedSizeInBits =
llvm::RoundUpToAlignment(getSizeInBits(),
Context.toBits(UnpackedAlignment));
CharUnits UnpackedSize = Context.toCharUnitsFromBits(UnpackedSizeInBits);
setSize(llvm::RoundUpToAlignment(getSizeInBits(), Context.toBits(Alignment)));
// Set the size to the final size.
setSize(RoundedSize);
unsigned CharBitNum = Context.getTargetInfo().getCharWidth();
if (const RecordDecl *RD = dyn_cast<RecordDecl>(D)) {
@ -2255,7 +2273,7 @@ RecordLayoutBuilder::updateExternalFieldOffset(const FieldDecl *Field,
if (InferAlignment && ExternalFieldOffset < ComputedOffset) {
// The externally-supplied field offset is before the field offset we
// computed. Assume that the structure is packed.
Alignment = CharUnits::fromQuantity(1);
Alignment = CharUnits::One();
InferAlignment = false;
}

15
clang/test/CodeGenCXX/override-layout.cpp
View File

@ -1,7 +1,7 @@
// RUN: %clang_cc1 -fdump-record-layouts-simple %s 2> %t.layouts
// RUN: %clang_cc1 -fdump-record-layouts-simple %s > %t.before 2>&1
// RUN: %clang_cc1 -DPACKED= -DALIGNED16= -fdump-record-layouts-simple -foverride-record-layout=%t.layouts %s > %t.after 2>&1
// RUN: diff %t.before %t.after
// RUN: diff -u %t.before %t.after
// RUN: FileCheck %s < %t.after
// If not explicitly disabled, set PACKED to the packed attribute.
@ -54,11 +54,24 @@ struct PACKED X4 {
X4();
};
// CHECK: Type: struct X5
struct PACKED X5 {
union {
long a;
long b;
};
short l;
short r;
};
void use_structs() {
X0 x0s[sizeof(X0)];
X1 x1s[sizeof(X1)];
X2 x2s[sizeof(X2)];
X3 x3s[sizeof(X3)];
X4 x4s[sizeof(X4)];
X5 x5s[sizeof(X5)];
x4s[1].a = 1;
x5s[1].a = 17;
}