[PATCH] D98068: Remove asserts for LocalInstantiationScope

[Yaxun Liu via Phabricator via cfe-commits]

yaxunl created this revision.
yaxunl added reviewers: rsmith, rjmccall, tra.
yaxunl requested review of this revision.

A lambda in a function template may be recursively instantiated as the following example:

  template <unsigned v>
  struct Number
  {
     static constexpr unsigned value = v;
  };
  
  template <unsigned IBegin = 0,
            unsigned IEnd = 1>
  constexpr auto fun1(Number<IBegin> = Number<0>{}, Number<IEnd>  = Number<1>{})
  {
    auto f = [&](auto fs, auto i) {
      if constexpr(i.value > 0)
      {
        return fs(fs, Number<IBegin>{});
      }
    };
  
    return f(f, Number<IEnd>{});
  }
  
  
  void fun2() {
    fun1();
  }

The recursive lambda will cause a bunch of lambda's instantiated, one inside another.
For each instantiation, clang asserts any formal arguments do not show up as formal
arguments of its outer instantiation. If these instantiations are not originated from the
same lambda, this is true. Unfortunately this is not true for recursive lambda's.


https://reviews.llvm.org/D98068

Files:
  clang/lib/Sema/SemaTemplateInstantiate.cpp
  clang/test/SemaCXX/recursive-lambda.cpp


Index: clang/test/SemaCXX/recursive-lambda.cpp
===================================================================
--- /dev/null
+++ clang/test/SemaCXX/recursive-lambda.cpp
@@ -0,0 +1,30 @@
+// RUN: %clang_cc1 -std=c++17 -fsyntax-only -verify %s
+
+// expected-no-diagnostics
+
+// Check recursive instantiation of lambda does not cause assertion.
+
+template <unsigned v>
+struct Number
+{
+   static constexpr unsigned value = v;
+};
+
+template <unsigned IBegin = 0,
+          unsigned IEnd = 1>
+constexpr auto fun1(Number<IBegin> = Number<0>{}, Number<IEnd>  = Number<1>{})
+{
+  auto f = [&](auto fs, auto i) {
+    if constexpr(i.value > 0)
+    {
+      return fs(fs, Number<IBegin>{});
+    }
+  };
+
+  return f(f, Number<IEnd>{});
+}
+
+
+void fun2() {
+  fun1();
+}
Index: clang/lib/Sema/SemaTemplateInstantiate.cpp
===================================================================
--- clang/lib/Sema/SemaTemplateInstantiate.cpp
+++ clang/lib/Sema/SemaTemplateInstantiate.cpp
@@ -3621,15 +3621,6 @@
   D = getCanonicalParmVarDecl(D);
   llvm::PointerUnion<Decl *, DeclArgumentPack *> &Stored = LocalDecls[D];
   if (Stored.isNull()) {
-#ifndef NDEBUG
-    // It should not be present in any surrounding scope either.
-    LocalInstantiationScope *Current = this;
-    while (Current->CombineWithOuterScope && Current->Outer) {
-      Current = Current->Outer;
-      assert(Current->LocalDecls.find(D) == Current->LocalDecls.end() &&
-             "Instantiated local in inner and outer scopes");
-    }
-#endif
     Stored = Inst;
   } else if (DeclArgumentPack *Pack = Stored.dyn_cast<DeclArgumentPack *>()) {
     Pack->push_back(cast<VarDecl>(Inst));
@@ -3646,14 +3637,6 @@
 }
 
 void LocalInstantiationScope::MakeInstantiatedLocalArgPack(const Decl *D) {
-#ifndef NDEBUG
-  // This should be the first time we've been told about this decl.
-  for (LocalInstantiationScope *Current = this;
-       Current && Current->CombineWithOuterScope; Current = Current->Outer)
-    assert(Current->LocalDecls.find(D) == Current->LocalDecls.end() &&
-           "Creating local pack after instantiation of local");
-#endif
-
   D = getCanonicalParmVarDecl(D);
   llvm::PointerUnion<Decl *, DeclArgumentPack *> &Stored = LocalDecls[D];
   DeclArgumentPack *Pack = new DeclArgumentPack;


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