Remove some false positives when taking the address of packed members
Differential Revision: https://reviews.llvm.org/D23657
llvm-svn: 286798
diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index 6956b06..8d71995 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -11696,7 +11696,8 @@
}
void Sema::DiscardMisalignedMemberAddress(const Type *T, Expr *E) {
- if (!T->isPointerType())
+ E = E->IgnoreParens();
+ if (!T->isPointerType() && !T->isIntegerType())
return;
if (isa<UnaryOperator>(E) &&
cast<UnaryOperator>(E)->getOpcode() == UO_AddrOf) {
@@ -11705,7 +11706,9 @@
auto MA = std::find(MisalignedMembers.begin(), MisalignedMembers.end(),
MisalignedMember(Op));
if (MA != MisalignedMembers.end() &&
- Context.getTypeAlignInChars(T->getPointeeType()) <= MA->Alignment)
+ (T->isIntegerType() ||
+ (T->isPointerType() &&
+ Context.getTypeAlignInChars(T->getPointeeType()) <= MA->Alignment)))
MisalignedMembers.erase(MA);
}
}
@@ -11713,28 +11716,103 @@
void Sema::RefersToMemberWithReducedAlignment(
Expr *E,
- std::function<void(Expr *, RecordDecl *, ValueDecl *, CharUnits)> Action) {
+ std::function<void(Expr *, RecordDecl *, FieldDecl *, CharUnits)> Action) {
const auto *ME = dyn_cast<MemberExpr>(E);
- while (ME && isa<FieldDecl>(ME->getMemberDecl())) {
+ if (!ME)
+ return;
+
+ // For a chain of MemberExpr like "a.b.c.d" this list
+ // will keep FieldDecl's like [d, c, b].
+ SmallVector<FieldDecl *, 4> ReverseMemberChain;
+ const MemberExpr *TopME = nullptr;
+ bool AnyIsPacked = false;
+ do {
QualType BaseType = ME->getBase()->getType();
if (ME->isArrow())
BaseType = BaseType->getPointeeType();
RecordDecl *RD = BaseType->getAs<RecordType>()->getDecl();
ValueDecl *MD = ME->getMemberDecl();
- bool ByteAligned = Context.getTypeAlignInChars(MD->getType()).isOne();
- if (ByteAligned) // Attribute packed does not have any effect.
- break;
+ auto *FD = dyn_cast<FieldDecl>(MD);
+ // We do not care about non-data members.
+ if (!FD || FD->isInvalidDecl())
+ return;
- if (!ByteAligned &&
- (RD->hasAttr<PackedAttr>() || (MD->hasAttr<PackedAttr>()))) {
- CharUnits Alignment = std::min(Context.getTypeAlignInChars(MD->getType()),
- Context.getTypeAlignInChars(BaseType));
- // Notify that this expression designates a member with reduced alignment
- Action(E, RD, MD, Alignment);
- break;
+ AnyIsPacked =
+ AnyIsPacked || (RD->hasAttr<PackedAttr>() || MD->hasAttr<PackedAttr>());
+ ReverseMemberChain.push_back(FD);
+
+ TopME = ME;
+ ME = dyn_cast<MemberExpr>(ME->getBase()->IgnoreParens());
+ } while (ME);
+ assert(TopME && "We did not compute a topmost MemberExpr!");
+
+ // Not the scope of this diagnostic.
+ if (!AnyIsPacked)
+ return;
+
+ const Expr *TopBase = TopME->getBase()->IgnoreParenImpCasts();
+ const auto *DRE = dyn_cast<DeclRefExpr>(TopBase);
+ // TODO: The innermost base of the member expression may be too complicated.
+ // For now, just disregard these cases. This is left for future
+ // improvement.
+ if (!DRE && !isa<CXXThisExpr>(TopBase))
+ return;
+
+ // Alignment expected by the whole expression.
+ CharUnits ExpectedAlignment = Context.getTypeAlignInChars(E->getType());
+
+ // No need to do anything else with this case.
+ if (ExpectedAlignment.isOne())
+ return;
+
+ // Synthesize offset of the whole access.
+ CharUnits Offset;
+ for (auto I = ReverseMemberChain.rbegin(); I != ReverseMemberChain.rend();
+ I++) {
+ Offset += Context.toCharUnitsFromBits(Context.getFieldOffset(*I));
+ }
+
+ // Compute the CompleteObjectAlignment as the alignment of the whole chain.
+ CharUnits CompleteObjectAlignment = Context.getTypeAlignInChars(
+ ReverseMemberChain.back()->getParent()->getTypeForDecl());
+
+ // The base expression of the innermost MemberExpr may give
+ // stronger guarantees than the class containing the member.
+ if (DRE && !TopME->isArrow()) {
+ const ValueDecl *VD = DRE->getDecl();
+ if (!VD->getType()->isReferenceType())
+ CompleteObjectAlignment =
+ std::max(CompleteObjectAlignment, Context.getDeclAlign(VD));
+ }
+
+ // Check if the synthesized offset fulfills the alignment.
+ if (Offset % ExpectedAlignment != 0 ||
+ // It may fulfill the offset it but the effective alignment may still be
+ // lower than the expected expression alignment.
+ CompleteObjectAlignment < ExpectedAlignment) {
+ // If this happens, we want to determine a sensible culprit of this.
+ // Intuitively, watching the chain of member expressions from right to
+ // left, we start with the required alignment (as required by the field
+ // type) but some packed attribute in that chain has reduced the alignment.
+ // It may happen that another packed structure increases it again. But if
+ // we are here such increase has not been enough. So pointing the first
+ // FieldDecl that either is packed or else its RecordDecl is,
+ // seems reasonable.
+ FieldDecl *FD = nullptr;
+ CharUnits Alignment;
+ for (FieldDecl *FDI : ReverseMemberChain) {
+ if (FDI->hasAttr<PackedAttr>() ||
+ FDI->getParent()->hasAttr<PackedAttr>()) {
+ FD = FDI;
+ Alignment = std::min(
+ Context.getTypeAlignInChars(FD->getType()),
+ Context.getTypeAlignInChars(FD->getParent()->getTypeForDecl()));
+ break;
+ }
}
- ME = dyn_cast<MemberExpr>(ME->getBase());
+ assert(FD && "We did not find a packed FieldDecl!");
+ Action(E, FD->getParent(), FD, Alignment);
}
}