[PATCH] D86936: [clang] Limit the maximum level of fold-expr expansion.

[Haojian Wu via Phabricator via cfe-commits]

hokein created this revision.
hokein added a reviewer: sammccall.
Herald added a project: clang.
hokein requested review of this revision.

Introduce a new diagnostic, and respect the bracket-depth (256) by default.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D86936

Files:
  clang/include/clang/Basic/DiagnosticSemaKinds.td
  clang/lib/Sema/TreeTransform.h
  clang/test/SemaCXX/fold_expr_expansion_limit.cpp


Index: clang/test/SemaCXX/fold_expr_expansion_limit.cpp
===================================================================
--- /dev/null
+++ clang/test/SemaCXX/fold_expr_expansion_limit.cpp
@@ -0,0 +1,9 @@
+// RUN: %clang_cc1 -fsyntax-only -fbracket-depth 2 -verify -std=c++17 %s
+
+template <class T, T...V> struct seq {
+  constexpr bool zero() { return (true && ... && (V == 0)); }; // expected-error {{fold expression expansion level 3 exceeded maximum of 2}}
+};
+constexpr unsigned N = 3;
+auto x = __make_integer_seq<seq, int, N>{};
+static_assert(!x.zero(), ""); // expected-error {{static_assert expression is not an integral constant expression}} \
+                                 expected-note {{in instantiation of member function}}
Index: clang/lib/Sema/TreeTransform.h
===================================================================
--- clang/lib/Sema/TreeTransform.h
+++ clang/lib/Sema/TreeTransform.h
@@ -13192,6 +13192,13 @@
         Callee, E->getBeginLoc(), LHS.get(), E->getOperator(),
         E->getEllipsisLoc(), RHS.get(), E->getEndLoc(), NumExpansions);
   }
+  if (NumExpansions && SemaRef.getLangOpts().BracketDepth < NumExpansions) {
+    SemaRef.Diag(E->getEllipsisLoc(),
+                 clang::diag::err_fold_expression_expansion_exceeded)
+        << *NumExpansions << SemaRef.getLangOpts().BracketDepth
+        << E->getSourceRange();
+    return ExprError();
+  }
 
   // The transform has determined that we should perform an elementwise
   // expansion of the pattern. Do so.
Index: clang/include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -5089,6 +5089,8 @@
   "with no fallback value">;
 def err_fold_expression_bad_operand : Error<
   "expression not permitted as operand of fold expression">;
+def err_fold_expression_expansion_exceeded: Error<
+  "fold expression expansion level %0 exceeded maximum of %1">;
 
 def err_unexpected_typedef : Error<
   "unexpected type name %0: expected expression">;


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