[AST] Accept identical TypeConstraint referring to other template

parameters.

The current implementation to judge the similarity of TypeConstraint in
ASTContext::isSameTemplateParameter is problematic, it couldn't handle
the following case:

```C++
template <__integer_like _Tp, C<_Tp> Sentinel>
constexpr _Tp operator()(_Tp &&__t, Sentinel &&last) const {
    return __t;
}
```

When we see 2 such declarations from different modules, we would judge
their similarity by `ASTContext::isSame*` methods. But problems come for
the TypeConstraint. Originally, we would profile each argument one by
one. But it is not right. Since the profiling result of `_Tp` would
refer to two different template type declarations. So it would get
different results. It is right since the `_Tp` in different modules
refers to different declarations indeed. So the same declaration in
different modules would meet incorrect our-checking results.

It is not the thing we want. We want to know if the TypeConstraint have
the same expression.

Reviewer: vsapsai, ilya-biryukov

Differential Revision: https://reviews.llvm.org/D129068

clang/include/clang/AST/ASTContext.h

@@ -130,6 +130,7 @@ class TemplateDecl;
 class TemplateParameterList;
 class TemplateTemplateParmDecl;
 class TemplateTypeParmDecl;
+class TypeConstraint;
 class UnresolvedSetIterator;
 class UsingShadowDecl;
 class VarTemplateDecl;
@@ -2664,6 +2665,18 @@ public:
   /// that they may be used in declarations of the same template.
   bool isSameTemplateParameter(const NamedDecl *X, const NamedDecl *Y) const;
 
+  /// Determine whether two 'requires' expressions are similar enough that they
+  /// may be used in re-declarations.
+  ///
+  /// Use of 'requires' isn't mandatory, works with constraints expressed in
+  /// other ways too.
+  bool isSameConstraintExpr(const Expr *XCE, const Expr *YCE) const;
+
+  /// Determine whether two type contraint are similar enough that they could
+  /// used in declarations of the same template.
+  bool isSameTypeConstraint(const TypeConstraint *XTC,
+                            const TypeConstraint *YTC) const;
+
   /// Determine whether two default template arguments are similar enough
   /// that they may be used in declarations of the same template.
   bool isSameDefaultTemplateArgument(const NamedDecl *X,

clang/lib/AST/ASTContext.cpp

@@ -6218,6 +6218,57 @@ bool ASTContext::hasSameTemplateName(const TemplateName &X,
          getCanonicalTemplateName(Y).getAsVoidPointer();
 }
 
+bool ASTContext::isSameConstraintExpr(const Expr *XCE, const Expr *YCE) const {
+  if (!XCE != !YCE)
+    return false;
+
+  if (!XCE)
+    return true;
+
+  llvm::FoldingSetNodeID XCEID, YCEID;
+  XCE->Profile(XCEID, *this, /*Canonical=*/true);
+  YCE->Profile(YCEID, *this, /*Canonical=*/true);
+  return XCEID == YCEID;
+}
+
+bool ASTContext::isSameTypeConstraint(const TypeConstraint *XTC,
+                                      const TypeConstraint *YTC) const {
+  if (!XTC != !YTC)
+    return false;
+
+  if (!XTC)
+    return true;
+
+  auto *NCX = XTC->getNamedConcept();
+  auto *NCY = YTC->getNamedConcept();
+  if (!NCX || !NCY || !isSameEntity(NCX, NCY))
+    return false;
+  if (XTC->hasExplicitTemplateArgs() != YTC->hasExplicitTemplateArgs())
+    return false;
+  if (XTC->hasExplicitTemplateArgs())
+    if (XTC->getTemplateArgsAsWritten()->NumTemplateArgs !=
+        YTC->getTemplateArgsAsWritten()->NumTemplateArgs)
+      return false;
+
+  // Compare slowly by profiling.
+  //
+  // We couldn't compare the profiling result for the template
+  // args here. Consider the following example in different modules:
+  //
+  // template <__integer_like _Tp, C<_Tp> Sentinel>
+  // constexpr _Tp operator()(_Tp &&__t, Sentinel &&last) const {
+  //   return __t;
+  // }
+  //
+  // When we compare the profiling result for `C<_Tp>` in different
+  // modules, it will compare the type of `_Tp` in different modules.
+  // However, the type of `_Tp` in different modules refer to different
+  // types here naturally. So we couldn't compare the profiling result
+  // for the template args directly.
+  return isSameConstraintExpr(XTC->getImmediatelyDeclaredConstraint(),
+                              YTC->getImmediatelyDeclaredConstraint());
+}
+
 bool ASTContext::isSameTemplateParameter(const NamedDecl *X,
                                          const NamedDecl *Y) const {
   if (X->getKind() != Y->getKind())
@@ -6229,32 +6280,8 @@ bool ASTContext::isSameTemplateParameter(const NamedDecl *X,
       return false;
     if (TX->hasTypeConstraint() != TY->hasTypeConstraint())
       return false;
-    const TypeConstraint *TXTC = TX->getTypeConstraint();
+    return isSameTypeConstraint(TX->getTypeConstraint(),
-    const TypeConstraint *TYTC = TY->getTypeConstraint();
+                                TY->getTypeConstraint());
-    if (!TXTC != !TYTC)
-      return false;
-    if (TXTC && TYTC) {
-      auto *NCX = TXTC->getNamedConcept();
-      auto *NCY = TYTC->getNamedConcept();
-      if (!NCX || !NCY || !isSameEntity(NCX, NCY))
-        return false;
-      if (TXTC->hasExplicitTemplateArgs() != TYTC->hasExplicitTemplateArgs())
-        return false;
-      if (TXTC->hasExplicitTemplateArgs()) {
-        auto *TXTCArgs = TXTC->getTemplateArgsAsWritten();
-        auto *TYTCArgs = TYTC->getTemplateArgsAsWritten();
-        if (TXTCArgs->NumTemplateArgs != TYTCArgs->NumTemplateArgs)
-          return false;
-        llvm::FoldingSetNodeID XID, YID;
-        for (auto &ArgLoc : TXTCArgs->arguments())
-          ArgLoc.getArgument().Profile(XID, X->getASTContext());
-        for (auto &ArgLoc : TYTCArgs->arguments())
-          ArgLoc.getArgument().Profile(YID, Y->getASTContext());
-        if (XID != YID)
-          return false;
-      }
-    }
-    return true;
   }
 
   if (auto *TX = dyn_cast<NonTypeTemplateParmDecl>(X)) {
@@ -6279,19 +6306,7 @@ bool ASTContext::isSameTemplateParameterList(
     if (!isSameTemplateParameter(X->getParam(I), Y->getParam(I)))
       return false;
 
-  const Expr *XRC = X->getRequiresClause();
+  return isSameConstraintExpr(X->getRequiresClause(), Y->getRequiresClause());
-  const Expr *YRC = Y->getRequiresClause();
-  if (!XRC != !YRC)
-    return false;
-  if (XRC) {
-    llvm::FoldingSetNodeID XRCID, YRCID;
-    XRC->Profile(XRCID, *this, /*Canonical=*/true);
-    YRC->Profile(YRCID, *this, /*Canonical=*/true);
-    if (XRCID != YRCID)
-      return false;
-  }
-
-  return true;
 }
 
 bool ASTContext::isSameDefaultTemplateArgument(const NamedDecl *X,
@@ -6489,17 +6504,9 @@ bool ASTContext::isSameEntity(const NamedDecl *X, const NamedDecl *Y) const {
         return false;
     }
 
-    const Expr *XRC = FuncX->getTrailingRequiresClause();
+    if (!isSameConstraintExpr(FuncX->getTrailingRequiresClause(),
-    const Expr *YRC = FuncY->getTrailingRequiresClause();
+                              FuncY->getTrailingRequiresClause()))
-    if (!XRC != !YRC)
       return false;
-    if (XRC) {
-      llvm::FoldingSetNodeID XRCID, YRCID;
-      XRC->Profile(XRCID, *this, /*Canonical=*/true);
-      YRC->Profile(YRCID, *this, /*Canonical=*/true);
-      if (XRCID != YRCID)
-        return false;
-    }
 
     auto GetTypeAsWritten = [](const FunctionDecl *FD) {
       // Map to the first declaration that we've already merged into this one.

clang/test/Modules/concept.cppm

@@ -3,6 +3,7 @@
 // RUN: split-file %s %t
 //
 // RUN: %clang_cc1 -std=c++20 %t/A.cppm -emit-module-interface -o %t/A.pcm
+// RUN: %clang_cc1 -std=c++20 -fprebuilt-module-path=%t -I%t -DDIFFERENT %t/B.cppm -verify
 // RUN: %clang_cc1 -std=c++20 -fprebuilt-module-path=%t -I%t %t/B.cppm -verify
 
 //--- foo.h
@@ -18,6 +19,9 @@ concept __integer_like = true;
 template <class _Tp>
 concept __member_size = requires(_Tp &&t) { t.size(); };
 
+template <class First, class Second>
+concept C = requires(First x, Second y) { x + y; };
+
 struct A {
 public:
   template <Range T>
@@ -29,6 +33,29 @@ struct __fn {
   constexpr __integer_like auto operator()(_Tp&& __t) const {
     return __t.size();
   }
+
+  template <__integer_like _Tp, C<_Tp> Sentinel>
+  constexpr _Tp operator()(_Tp &&__t, Sentinel &&last) const {
+    return __t;
+  }
+
+  template <template <class> class H, class S, C<H<S>> Sentinel>
+  constexpr H<S> operator()(H<S> &&__s, Sentinel &&last) const {
+    return __s;
+  }
+
+// Tests that we could find different concept definition indeed.
+#ifndef DIFFERENT
+  template <__integer_like _Tp, __integer_like _Up, C<_Tp> Sentinel>
+  constexpr _Tp operator()(_Tp &&__t, _Up _u, Sentinel &&last) const {
+    return __t;
+  }
+#else
+  template <__integer_like _Tp, __integer_like _Up, C<_Up> Sentinel>
+  constexpr _Tp operator()(_Tp &&__t, _Up _u, Sentinel &&last) const {
+    return __t;
+  }
+#endif
 };
 #endif
 
@@ -38,12 +65,23 @@ module;
 export module A;
 
 //--- B.cppm
-// expected-no-diagnostics
 module;
 #include "foo.h"
 export module B;
 import A;
 
+#ifdef DIFFERENT
+// expected-error@foo.h:41 {{'__fn::operator()' from module 'A.<global>' is not present in definition of '__fn' provided earlier}}
+// expected-note@* 1+{{declaration of 'operator()' does not match}}
+#else
+// expected-no-diagnostics
+#endif
+
+template <class T>
+struct U {
+  auto operator+(U) { return 0; }
+};
+
 void foo() {
     A a;
     struct S {
@@ -51,4 +89,8 @@ void foo() {
         auto operator+(S s) { return 0; }
     };
     __fn{}(S());
+    __fn{}(S(), S());
+    __fn{}(S(), S(), S());
+
+    __fn{}(U<int>(), U<int>());
 }