[clang] [Clang] Defer the instantiation of explicit-specifier until constraint checking completes (PR #70548)

via cfe-commits cfe-commits at lists.llvm.org
Sat Oct 28 03:49:37 PDT 2023


https://github.com/LYP951018 updated https://github.com/llvm/llvm-project/pull/70548

>From 4f8111b58324d5b670311717d36654f64e6dac01 Mon Sep 17 00:00:00 2001
From: letrec <liuyupei951018 at hotmail.com>
Date: Sat, 28 Oct 2023 18:05:36 +0800
Subject: [PATCH] Defer the instantiation of explicit-specifier after
 constraint checking

---
 clang/docs/ReleaseNotes.rst                   |  4 ++
 clang/include/clang/Sema/Sema.h               |  3 +
 clang/lib/Sema/SemaTemplateDeduction.cpp      | 56 +++++++++++++++++++
 .../lib/Sema/SemaTemplateInstantiateDecl.cpp  | 40 ++++++++-----
 .../SemaCXX/cxx2a-explicit-bool-deferred.cpp  | 31 ++++++++++
 5 files changed, 120 insertions(+), 14 deletions(-)
 create mode 100644 clang/test/SemaCXX/cxx2a-explicit-bool-deferred.cpp

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 2595737e8b3b143..203111b829bd0c6 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -670,6 +670,10 @@ Bug Fixes to C++ Support
   default initializing a base class in a constant expression context. Fixes:
   (`#69890 <https://github.com/llvm/llvm-project/issues/69890>`_)
 
+- Clang now defers the instantiation of explicit specifier until constraint checking
+  completes (except deduction guides). Fixes:
+  (`#59827 <https://github.com/llvm/llvm-project/issues/59827>`_)
+
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^
 - Fixed an import failure of recursive friend class template.
diff --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h
index 1e9752345ffd173..93fd6507db3d78a 100644
--- a/clang/include/clang/Sema/Sema.h
+++ b/clang/include/clang/Sema/Sema.h
@@ -10430,6 +10430,9 @@ class Sema final {
                                   const CXXConstructorDecl *Tmpl,
                             const MultiLevelTemplateArgumentList &TemplateArgs);
 
+  ExplicitSpecifier instantiateExplicitSpecifier(
+      const MultiLevelTemplateArgumentList &TemplateArgs, ExplicitSpecifier ES);
+
   NamedDecl *FindInstantiatedDecl(SourceLocation Loc, NamedDecl *D,
                           const MultiLevelTemplateArgumentList &TemplateArgs,
                           bool FindingInstantiatedContext = false);
diff --git a/clang/lib/Sema/SemaTemplateDeduction.cpp b/clang/lib/Sema/SemaTemplateDeduction.cpp
index 0b3f0247ea3bee3..e75e46aa5228812 100644
--- a/clang/lib/Sema/SemaTemplateDeduction.cpp
+++ b/clang/lib/Sema/SemaTemplateDeduction.cpp
@@ -3553,6 +3553,53 @@ static unsigned getPackIndexForParam(Sema &S,
   llvm_unreachable("parameter index would not be produced from template");
 }
 
+// if `Specialization` is a `CXXConstructorDecl` or `CXXConversionDecl`
+// we try to instantiate and update its explicit specifier after constraint
+// checking.
+static Sema::TemplateDeductionResult
+tryInstantiateExplicitSpecifier(Sema &S, FunctionDecl *Specialization,
+                                const MultiLevelTemplateArgumentList &SubstArgs,
+                                TemplateDeductionInfo &Info,
+                                FunctionTemplateDecl *FunctionTemplate,
+                                ArrayRef<TemplateArgument> DeducedArgs) {
+
+  const auto TryInstantiateExplicitSpecifierForSingleDecl =
+      [&](auto *ExplicitDecl) {
+        ExplicitSpecifier ExplicitSpecifier =
+            ExplicitDecl->getExplicitSpecifier();
+        Expr *const Expr = ExplicitSpecifier.getExpr();
+        if (!Expr) {
+          return Sema::TDK_Success;
+        }
+        if (!Expr->isValueDependent()) {
+          return Sema::TDK_Success;
+        }
+        Sema::InstantiatingTemplate Inst(
+            S, Info.getLocation(), FunctionTemplate, DeducedArgs,
+            Sema::CodeSynthesisContext::DeducedTemplateArgumentSubstitution,
+            Info);
+        const auto Instantiated =
+            S.instantiateExplicitSpecifier(SubstArgs, ExplicitSpecifier);
+        if (Instantiated.isInvalid()) {
+          ExplicitDecl->setInvalidDecl(true);
+          return clang::Sema::TDK_SubstitutionFailure;
+        }
+        ExplicitDecl->setExplicitSpecifier(Instantiated);
+        return clang::Sema::TDK_Success;
+      };
+  Sema::TemplateDeductionResult DeductionResult = clang::Sema::TDK_Success;
+  if (CXXConstructorDecl *ConstructorDecl =
+          dyn_cast_or_null<CXXConstructorDecl>(Specialization)) {
+    DeductionResult =
+        TryInstantiateExplicitSpecifierForSingleDecl(ConstructorDecl);
+  } else if (CXXConversionDecl *ConversionDecl =
+                 dyn_cast_or_null<CXXConversionDecl>(Specialization)) {
+    DeductionResult =
+        TryInstantiateExplicitSpecifierForSingleDecl(ConversionDecl);
+  }
+  return DeductionResult;
+}
+
 /// Finish template argument deduction for a function template,
 /// checking the deduced template arguments for completeness and forming
 /// the function template specialization.
@@ -3682,6 +3729,15 @@ Sema::TemplateDeductionResult Sema::FinishTemplateArgumentDeduction(
     }
   }
 
+  // We skipped the instantiation of the explicit-specifier during subst the
+  // decl before. Now, we try to instantiate it back if the Specialization is a
+  // constructor or a conversion.
+  if (TDK_Success !=
+      tryInstantiateExplicitSpecifier(*this, Specialization, SubstArgs, Info,
+                                      FunctionTemplate, DeducedArgs)) {
+    return TDK_SubstitutionFailure;
+  }
+
   if (OriginalCallArgs) {
     // C++ [temp.deduct.call]p4:
     //   In general, the deduction process attempts to find template argument
diff --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
index 78a7892a35a320b..163dbef03e80a4d 100644
--- a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -563,18 +563,16 @@ static void instantiateDependentAMDGPUFlatWorkGroupSizeAttr(
   S.addAMDGPUFlatWorkGroupSizeAttr(New, Attr, MinExpr, MaxExpr);
 }
 
-static ExplicitSpecifier
-instantiateExplicitSpecifier(Sema &S,
-                             const MultiLevelTemplateArgumentList &TemplateArgs,
-                             ExplicitSpecifier ES, FunctionDecl *New) {
+ExplicitSpecifier Sema::instantiateExplicitSpecifier(
+    const MultiLevelTemplateArgumentList &TemplateArgs, ExplicitSpecifier ES) {
   if (!ES.getExpr())
     return ES;
   Expr *OldCond = ES.getExpr();
   Expr *Cond = nullptr;
   {
     EnterExpressionEvaluationContext Unevaluated(
-        S, Sema::ExpressionEvaluationContext::ConstantEvaluated);
-    ExprResult SubstResult = S.SubstExpr(OldCond, TemplateArgs);
+        *this, Sema::ExpressionEvaluationContext::ConstantEvaluated);
+    ExprResult SubstResult = SubstExpr(OldCond, TemplateArgs);
     if (SubstResult.isInvalid()) {
       return ExplicitSpecifier::Invalid();
     }
@@ -582,7 +580,7 @@ instantiateExplicitSpecifier(Sema &S,
   }
   ExplicitSpecifier Result(Cond, ES.getKind());
   if (!Cond->isTypeDependent())
-    S.tryResolveExplicitSpecifier(Result);
+    tryResolveExplicitSpecifier(Result);
   return Result;
 }
 
@@ -2073,8 +2071,8 @@ Decl *TemplateDeclInstantiator::VisitFunctionDecl(
 
   ExplicitSpecifier InstantiatedExplicitSpecifier;
   if (auto *DGuide = dyn_cast<CXXDeductionGuideDecl>(D)) {
-    InstantiatedExplicitSpecifier = instantiateExplicitSpecifier(
-        SemaRef, TemplateArgs, DGuide->getExplicitSpecifier(), DGuide);
+    InstantiatedExplicitSpecifier = SemaRef.instantiateExplicitSpecifier(
+        TemplateArgs, DGuide->getExplicitSpecifier());
     if (InstantiatedExplicitSpecifier.isInvalid())
       return nullptr;
   }
@@ -2453,11 +2451,25 @@ Decl *TemplateDeclInstantiator::VisitCXXMethodDecl(
     }
   }
 
-  ExplicitSpecifier InstantiatedExplicitSpecifier =
-      instantiateExplicitSpecifier(SemaRef, TemplateArgs,
-                                   ExplicitSpecifier::getFromDecl(D), D);
-  if (InstantiatedExplicitSpecifier.isInvalid())
-    return nullptr;
+  auto InstantiatedExplicitSpecifier = ExplicitSpecifier::getFromDecl(D);
+  // deduction guides need this
+  const bool CouldInstantiate =
+      InstantiatedExplicitSpecifier.getExpr() == nullptr ||
+      !InstantiatedExplicitSpecifier.getExpr()->isValueDependent();
+
+  // Delay the instantiation of the explicit-specifier until after the
+  // constraints are checked during template argument deduction.
+  if (CouldInstantiate ||
+      SemaRef.CodeSynthesisContexts.back().Kind !=
+          Sema::CodeSynthesisContext::DeducedTemplateArgumentSubstitution) {
+    InstantiatedExplicitSpecifier = SemaRef.instantiateExplicitSpecifier(
+        TemplateArgs, InstantiatedExplicitSpecifier);
+
+    if (InstantiatedExplicitSpecifier.isInvalid())
+      return nullptr;
+  } else {
+    InstantiatedExplicitSpecifier.setKind(ExplicitSpecKind::Unresolved);
+  }
 
   // Implicit destructors/constructors created for local classes in
   // DeclareImplicit* (see SemaDeclCXX.cpp) might not have an associated TSI.
diff --git a/clang/test/SemaCXX/cxx2a-explicit-bool-deferred.cpp b/clang/test/SemaCXX/cxx2a-explicit-bool-deferred.cpp
new file mode 100644
index 000000000000000..4d667008f2e2763
--- /dev/null
+++ b/clang/test/SemaCXX/cxx2a-explicit-bool-deferred.cpp
@@ -0,0 +1,31 @@
+// RUN: %clang_cc1 -fsyntax-only -verify -std=c++2a %s
+
+template <typename T1, typename T2> struct is_same {
+  static constexpr bool value = false;
+};
+
+template <typename T> struct is_same<T, T> {
+  static constexpr bool value = true;
+};
+
+template <class T, class U>
+concept SameHelper = is_same<T, U>::value;
+template <class T, class U>
+concept same_as = SameHelper<T, U> && SameHelper<U, T>;
+
+namespace deferred_instantiation {
+template <class X> constexpr X do_not_instantiate() { return nullptr; }
+
+struct T {
+  template <same_as<float> X> explicit(do_not_instantiate<X>()) T(X) {}
+
+  T(int) {}
+};
+
+T t(5);
+// expected-error at 17{{cannot initialize}}
+// expected-note at 20{{in instantiation of function template specialization}}
+// expected-note at 30{{while substituting deduced template arguments}}
+// expected-note at 30{{in instantiation of function template specialization}}
+T t2(5.0f);
+} // namespace deferred_instantiation



More information about the cfe-commits mailing list