[ExprConstant] Fix PR28314 - crash while evluating objectsize.

This fixes a crash in code like:
```
struct A {
  struct B b;
  char c[1];
}

int foo(struct A* a) { return __builtin_object_size(a->c, 0); }
```

We wouldn't check whether the structs we were examining were invalid,
and getting the layout of an invalid struct is (unsurprisingly) A Bad
Thing. With this patch, we'll always return conservatively if we see an
invalid struct, since I'm assuming the presence of an invalid struct
means that our compilation failed (so having a conservative result isn't
such a big deal).

llvm-svn: 273911

1 files changed, 18 insertions, 10 deletions

diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index e14330cf60e..6771175ba6d 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -6540,25 +6540,32 @@ static const Expr *ignorePointerCastsAndParens(const Expr *E) {
 ///
 /// Please note: this function is specialized for how __builtin_object_size
 /// views "objects".
+///
+/// If this encounters an invalid RecordDecl, it will always return true.
 static bool isDesignatorAtObjectEnd(const ASTContext &Ctx, const LValue &LVal) {
   assert(!LVal.Designator.Invalid);
 
-  auto IsLastFieldDecl = [&Ctx](const FieldDecl *FD) {
-    if (FD->getParent()->isUnion())
+  auto IsLastOrInvalidFieldDecl = [&Ctx](const FieldDecl *FD, bool &Invalid) {
+    const RecordDecl *Parent = FD->getParent();
+    Invalid = Parent->isInvalidDecl();
+    if (Invalid || Parent->isUnion())
       return true;
-    const ASTRecordLayout &Layout = Ctx.getASTRecordLayout(FD->getParent());
+    const ASTRecordLayout &Layout = Ctx.getASTRecordLayout(Parent);
     return FD->getFieldIndex() + 1 == Layout.getFieldCount();
   };
 
   auto &Base = LVal.getLValueBase();
   if (auto *ME = dyn_cast_or_null<MemberExpr>(Base.dyn_cast<const Expr *>())) {
     if (auto *FD = dyn_cast<FieldDecl>(ME->getMemberDecl())) {
-      if (!IsLastFieldDecl(FD))
-        return false;
+      bool Invalid;
+      if (!IsLastOrInvalidFieldDecl(FD, Invalid))
+        return Invalid;
     } else if (auto *IFD = dyn_cast<IndirectFieldDecl>(ME->getMemberDecl())) {
-      for (auto *FD : IFD->chain())
-        if (!IsLastFieldDecl(cast<FieldDecl>(FD)))
-          return false;
+      for (auto *FD : IFD->chain()) {
+        bool Invalid;
+        if (!IsLastOrInvalidFieldDecl(cast<FieldDecl>(FD), Invalid))
+          return Invalid;
+      }
     }
   }
 
@@ -6581,8 +6588,9 @@ static bool isDesignatorAtObjectEnd(const ASTContext &Ctx, const LValue &LVal) {
         return false;
       BaseType = CT->getElementType();
     } else if (auto *FD = getAsField(LVal.Designator.Entries[I])) {
-      if (!IsLastFieldDecl(FD))
-        return false;
+      bool Invalid;
+      if (!IsLastOrInvalidFieldDecl(FD, Invalid))
+        return Invalid;
       BaseType = FD->getType();
     } else {
       assert(getAsBaseClass(LVal.Designator.Entries[I]) != nullptr &&