Fix the computation of alignment for fields of packed+aligned structs.
Part of the fix for PR8413.
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@123904 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/AST/ASTContext.cpp b/lib/AST/ASTContext.cpp
index d1ac008..043d56a 100644
--- a/lib/AST/ASTContext.cpp
+++ b/lib/AST/ASTContext.cpp
@@ -590,8 +590,11 @@
}
}
+ // If we're using the align attribute only, just ignore everything
+ // else about the declaration and its type.
if (UseAlignAttrOnly) {
- // ignore type of value
+ // do nothing
+
} else if (const ValueDecl *VD = dyn_cast<ValueDecl>(D)) {
QualType T = VD->getType();
if (const ReferenceType* RT = T->getAs<ReferenceType>()) {
@@ -617,11 +620,30 @@
}
Align = std::max(Align, getPreferredTypeAlign(T.getTypePtr()));
}
- if (const FieldDecl *FD = dyn_cast<FieldDecl>(VD)) {
- // In the case of a field in a packed struct, we want the minimum
- // of the alignment of the field and the alignment of the struct.
- Align = std::min(Align,
- getPreferredTypeAlign(FD->getParent()->getTypeForDecl()));
+
+ // Fields can be subject to extra alignment constraints, like if
+ // the field is packed, the struct is packed, or the struct has a
+ // a max-field-alignment constraint (#pragma pack). So calculate
+ // the actual alignment of the field within the struct, and then
+ // (as we're expected to) constrain that by the alignment of the type.
+ if (const FieldDecl *field = dyn_cast<FieldDecl>(VD)) {
+ // So calculate the alignment of the field.
+ const ASTRecordLayout &layout = getASTRecordLayout(field->getParent());
+
+ // Start with the record's overall alignment.
+ unsigned fieldAlign = layout.getAlignment();
+
+ // Use the GCD of that and the offset within the record.
+ uint64_t offset = layout.getFieldOffset(field->getFieldIndex());
+ if (offset > 0) {
+ // Alignment is always a power of 2, so the GCD will be a power of 2,
+ // which means we get to do this crazy thing instead of Euclid's.
+ uint64_t lowBitOfOffset = offset & (~offset + 1);
+ if (lowBitOfOffset < fieldAlign)
+ fieldAlign = static_cast<unsigned>(lowBitOfOffset);
+ }
+
+ Align = std::min(Align, fieldAlign);
}
}
diff --git a/lib/AST/Decl.cpp b/lib/AST/Decl.cpp
index 9e2e876..b1da849 100644
--- a/lib/AST/Decl.cpp
+++ b/lib/AST/Decl.cpp
@@ -1881,6 +1881,25 @@
return false;
}
+unsigned FieldDecl::getFieldIndex() const {
+ if (CachedFieldIndex) return CachedFieldIndex - 1;
+
+ unsigned index = 0;
+ RecordDecl::field_iterator
+ i = getParent()->field_begin(), e = getParent()->field_end();
+ while (true) {
+ assert(i != e && "failed to find field in parent!");
+ if (*i == this)
+ break;
+
+ ++i;
+ ++index;
+ }
+
+ CachedFieldIndex = index + 1;
+ return index;
+}
+
//===----------------------------------------------------------------------===//
// TagDecl Implementation
//===----------------------------------------------------------------------===//
diff --git a/lib/AST/ExprConstant.cpp b/lib/AST/ExprConstant.cpp
index f262a4a..afce24e 100644
--- a/lib/AST/ExprConstant.cpp
+++ b/lib/AST/ExprConstant.cpp
@@ -1565,14 +1565,7 @@
return false;
RecordDecl *RD = RT->getDecl();
const ASTRecordLayout &RL = Info.Ctx.getASTRecordLayout(RD);
- unsigned i = 0;
- // FIXME: It would be nice if we didn't have to loop here!
- for (RecordDecl::field_iterator Field = RD->field_begin(),
- FieldEnd = RD->field_end();
- Field != FieldEnd; (void)++Field, ++i) {
- if (*Field == MemberDecl)
- break;
- }
+ unsigned i = MemberDecl->getFieldIndex();
assert(i < RL.getFieldCount() && "offsetof field in wrong type");
Result += Info.Ctx.toCharUnitsFromBits(RL.getFieldOffset(i));
CurrentType = MemberDecl->getType().getNonReferenceType();