Fix #12861 Hang in valueFlowCondition() with huge array

lib/token.h

@@ -117,6 +117,7 @@ class CPPCHECKLIB Token {
         Token* mAstOperand1{};
         Token* mAstOperand2{};
         Token* mAstParent{};
+        Token* mAstTop{};
 
         // symbol database information
         const Scope* mScope{};
@@ -1557,6 +1558,9 @@ class CPPCHECKLIB Token {
      * @throws InternalError thrown on cyclic dependency
      */
     void astParent(Token* tok);
+    void astTop(Token * tok) {
+        mImpl->mAstTop = tok;
+    }
 
     Token * astOperand1() {
         return mImpl->mAstOperand1;
@@ -1597,13 +1601,19 @@ class CPPCHECKLIB Token {
 
     }
     RET_NONNULL Token *astTop() {
+        if (mImpl->mAstTop) {
+            return mImpl->mAstTop;
+        }
         Token *ret = this;
         while (ret->mImpl->mAstParent)
             ret = ret->mImpl->mAstParent;
         return ret;
     }
 
     RET_NONNULL const Token *astTop() const {
+        if (mImpl->mAstTop) {
+            return mImpl->mAstTop;
+        }
         const Token *ret = this;
         while (ret->mImpl->mAstParent)
             ret = ret->mImpl->mAstParent;

lib/tokenlist.cpp

@@ -1860,6 +1860,16 @@ void TokenList::createAst() const
             throw InternalError(tok, "Syntax Error: Infinite loop when creating AST.", InternalError::AST);
         tok = nextTok;
     }
+    for (Token *tok = mTokensFrontBack->front; tok; tok = tok ? tok->next() : nullptr) {
+        if (tok->astParent())
+            continue;
+        if (!tok->astOperand1() && !tok->astOperand2())
+            continue;
+        visitAstNodes(tok, [&](Token* child) {
+            child->astTop(tok);
+            return ChildrenToVisit::op1_and_op2;
+        });
+    }
 }
 
 namespace {