[clang] [Clang] Add attribute for consteval builtins; Declare constexpr builtins as constexpr in C++ (PR #91894)

[Mital Ashok via cfe-commits]

https://github.com/MitalAshok updated 
https://github.com/llvm/llvm-project/pull/91894

>From 56aed689dc5825fc5bacc6dfdff58ee0eaf71f82 Mon Sep 17 00:00:00 2001
From: Mital Ashok 
Date: Sun, 12 May 2024 19:48:24 +0100
Subject: [PATCH 1/3] [Clang] Add attribute for consteval builtins; Declare
 constexpr builtins as constexpr in C++

Also support redeclaring now-constexpr builtins without constexpr
---
 clang/include/clang/Basic/Builtins.h  |  5 +
 clang/include/clang/Basic/BuiltinsBase.td |  2 ++
 clang/lib/Sema/SemaDecl.cpp   | 15 +++
 clang/lib/Sema/SemaDeclCXX.cpp| 18 +-
 clang/lib/Sema/SemaExpr.cpp   |  8 ++--
 clang/test/Sema/builtin-redecl.cpp| 15 ++-
 6 files changed, 47 insertions(+), 16 deletions(-)

diff --git a/clang/include/clang/Basic/Builtins.h 
b/clang/include/clang/Basic/Builtins.h
index f955d21169556..e85ec5b2dca14 100644
--- a/clang/include/clang/Basic/Builtins.h
+++ b/clang/include/clang/Basic/Builtins.h
@@ -280,6 +280,11 @@ class Context {
 return strchr(getRecord(ID).Attributes, 'E') != nullptr;
   }
 
+  /// Returns true if this is an immediate (consteval) function
+  bool isImmediate(unsigned ID) const {
+return strchr(getRecord(ID).Attributes, 'G') != nullptr;
+  }
+
 private:
   const Info (unsigned ID) const;
 
diff --git a/clang/include/clang/Basic/BuiltinsBase.td 
b/clang/include/clang/Basic/BuiltinsBase.td
index 724747ec76d73..1196b9e15c10d 100644
--- a/clang/include/clang/Basic/BuiltinsBase.td
+++ b/clang/include/clang/Basic/BuiltinsBase.td
@@ -70,6 +70,8 @@ class VScanfFormat : IndexedAttribute<"S", I>;
 
 // Builtin can be constant evaluated
 def Constexpr : Attribute<"E">;
+// Builtin is immediate and must be constant evaluated. Implies Constexpr.
+def Consteval : Attribute<"EG">;
 
 // Builtin kinds
 // =
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index fb913034bd836..6b0a04585928a 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -2409,10 +2409,17 @@ FunctionDecl *Sema::CreateBuiltin(IdentifierInfo *II, 
QualType Type,
 Parent = CLinkageDecl;
   }
 
-  FunctionDecl *New = FunctionDecl::Create(Context, Parent, Loc, Loc, II, Type,
-   /*TInfo=*/nullptr, SC_Extern,
-   
getCurFPFeatures().isFPConstrained(),
-   false, Type->isFunctionProtoType());
+  ConstexprSpecKind ConstexprKind = ConstexprSpecKind::Unspecified;
+  if (getLangOpts().CPlusPlus && Context.BuiltinInfo.isConstantEvaluated(ID)) {
+ConstexprKind = ConstexprSpecKind::Constexpr;
+if (Context.BuiltinInfo.isImmediate(ID))
+  ConstexprKind = ConstexprSpecKind::Consteval;
+  }
+
+  FunctionDecl *New = FunctionDecl::Create(
+  Context, Parent, Loc, Loc, II, Type, /*TInfo=*/nullptr, SC_Extern,
+  getCurFPFeatures().isFPConstrained(), /*isInlineSpecified=*/false,
+  Type->isFunctionProtoType(), ConstexprKind);
   New->setImplicit();
   New->addAttr(BuiltinAttr::CreateImplicit(Context, ID));
 
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index 53238d355ea09..1b558d70f9b48 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -676,11 +676,19 @@ bool Sema::MergeCXXFunctionDecl(FunctionDecl *New, 
FunctionDecl *Old,
   // template has a constexpr specifier then all its declarations shall
   // contain the constexpr specifier.
   if (New->getConstexprKind() != Old->getConstexprKind()) {
-Diag(New->getLocation(), diag::err_constexpr_redecl_mismatch)
-<< New << static_cast(New->getConstexprKind())
-<< static_cast(Old->getConstexprKind());
-Diag(Old->getLocation(), diag::note_previous_declaration);
-Invalid = true;
+if (Old->getBuiltinID() &&
+Old->getConstexprKind() == ConstexprSpecKind::Constexpr &&
+New->getConstexprKind() == ConstexprSpecKind::Unspecified) {
+  // Except allow redeclaring a builtin as non-constexpr to match C
+  // redeclarations which will not be constexpr
+  New->setConstexprKind(ConstexprSpecKind::Constexpr);
+} else {
+  Diag(New->getLocation(), diag::err_constexpr_redecl_mismatch)
+  << New << static_cast(New->getConstexprKind())
+  << static_cast(Old->getConstexprKind());
+  Diag(Old->getLocation(), diag::note_previous_declaration);
+  Invalid = true;
+}
   } else if (!Old->getMostRecentDecl()->isInlined() && New->isInlined() &&
  Old->isDefined(Def) &&
  // If a friend function is inlined but does not have 'inline'
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index bb4b116fd73ca..39aa32526d2b1 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -7095,8 +7095,12 @@ ExprResult Sema::BuildResolvedCallExpr(Expr *Fn, 
NamedDecl *NDecl,
   }
 
   // Bail out 

[clang] [Clang] Add attribute for consteval builtins; Declare constexpr builtins as constexpr in C++ (PR #91894)

[Mital Ashok via cfe-commits]

https://github.com/MitalAshok updated 
https://github.com/llvm/llvm-project/pull/91894

>From 56aed689dc5825fc5bacc6dfdff58ee0eaf71f82 Mon Sep 17 00:00:00 2001
From: Mital Ashok 
Date: Sun, 12 May 2024 19:48:24 +0100
Subject: [PATCH 1/3] [Clang] Add attribute for consteval builtins; Declare
 constexpr builtins as constexpr in C++

Also support redeclaring now-constexpr builtins without constexpr
---
 clang/include/clang/Basic/Builtins.h  |  5 +
 clang/include/clang/Basic/BuiltinsBase.td |  2 ++
 clang/lib/Sema/SemaDecl.cpp   | 15 +++
 clang/lib/Sema/SemaDeclCXX.cpp| 18 +-
 clang/lib/Sema/SemaExpr.cpp   |  8 ++--
 clang/test/Sema/builtin-redecl.cpp| 15 ++-
 6 files changed, 47 insertions(+), 16 deletions(-)

diff --git a/clang/include/clang/Basic/Builtins.h 
b/clang/include/clang/Basic/Builtins.h
index f955d21169556..e85ec5b2dca14 100644
--- a/clang/include/clang/Basic/Builtins.h
+++ b/clang/include/clang/Basic/Builtins.h
@@ -280,6 +280,11 @@ class Context {
 return strchr(getRecord(ID).Attributes, 'E') != nullptr;
   }
 
+  /// Returns true if this is an immediate (consteval) function
+  bool isImmediate(unsigned ID) const {
+return strchr(getRecord(ID).Attributes, 'G') != nullptr;
+  }
+
 private:
   const Info (unsigned ID) const;
 
diff --git a/clang/include/clang/Basic/BuiltinsBase.td 
b/clang/include/clang/Basic/BuiltinsBase.td
index 724747ec76d73..1196b9e15c10d 100644
--- a/clang/include/clang/Basic/BuiltinsBase.td
+++ b/clang/include/clang/Basic/BuiltinsBase.td
@@ -70,6 +70,8 @@ class VScanfFormat : IndexedAttribute<"S", I>;
 
 // Builtin can be constant evaluated
 def Constexpr : Attribute<"E">;
+// Builtin is immediate and must be constant evaluated. Implies Constexpr.
+def Consteval : Attribute<"EG">;
 
 // Builtin kinds
 // =
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index fb913034bd836..6b0a04585928a 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -2409,10 +2409,17 @@ FunctionDecl *Sema::CreateBuiltin(IdentifierInfo *II, 
QualType Type,
 Parent = CLinkageDecl;
   }
 
-  FunctionDecl *New = FunctionDecl::Create(Context, Parent, Loc, Loc, II, Type,
-   /*TInfo=*/nullptr, SC_Extern,
-   
getCurFPFeatures().isFPConstrained(),
-   false, Type->isFunctionProtoType());
+  ConstexprSpecKind ConstexprKind = ConstexprSpecKind::Unspecified;
+  if (getLangOpts().CPlusPlus && Context.BuiltinInfo.isConstantEvaluated(ID)) {
+ConstexprKind = ConstexprSpecKind::Constexpr;
+if (Context.BuiltinInfo.isImmediate(ID))
+  ConstexprKind = ConstexprSpecKind::Consteval;
+  }
+
+  FunctionDecl *New = FunctionDecl::Create(
+  Context, Parent, Loc, Loc, II, Type, /*TInfo=*/nullptr, SC_Extern,
+  getCurFPFeatures().isFPConstrained(), /*isInlineSpecified=*/false,
+  Type->isFunctionProtoType(), ConstexprKind);
   New->setImplicit();
   New->addAttr(BuiltinAttr::CreateImplicit(Context, ID));
 
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index 53238d355ea09..1b558d70f9b48 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -676,11 +676,19 @@ bool Sema::MergeCXXFunctionDecl(FunctionDecl *New, 
FunctionDecl *Old,
   // template has a constexpr specifier then all its declarations shall
   // contain the constexpr specifier.
   if (New->getConstexprKind() != Old->getConstexprKind()) {
-Diag(New->getLocation(), diag::err_constexpr_redecl_mismatch)
-<< New << static_cast(New->getConstexprKind())
-<< static_cast(Old->getConstexprKind());
-Diag(Old->getLocation(), diag::note_previous_declaration);
-Invalid = true;
+if (Old->getBuiltinID() &&
+Old->getConstexprKind() == ConstexprSpecKind::Constexpr &&
+New->getConstexprKind() == ConstexprSpecKind::Unspecified) {
+  // Except allow redeclaring a builtin as non-constexpr to match C
+  // redeclarations which will not be constexpr
+  New->setConstexprKind(ConstexprSpecKind::Constexpr);
+} else {
+  Diag(New->getLocation(), diag::err_constexpr_redecl_mismatch)
+  << New << static_cast(New->getConstexprKind())
+  << static_cast(Old->getConstexprKind());
+  Diag(Old->getLocation(), diag::note_previous_declaration);
+  Invalid = true;
+}
   } else if (!Old->getMostRecentDecl()->isInlined() && New->isInlined() &&
  Old->isDefined(Def) &&
  // If a friend function is inlined but does not have 'inline'
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index bb4b116fd73ca..39aa32526d2b1 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -7095,8 +7095,12 @@ ExprResult Sema::BuildResolvedCallExpr(Expr *Fn, 
NamedDecl *NDecl,
   }
 
   // Bail out 

[clang] [Clang] Add attribute for consteval builtins; Declare constexpr builtins as constexpr in C++ (PR #91894)

[Mital Ashok via cfe-commits]

@@ -14,13 +14,18 @@ void __builtin_va_copy(double d);
 // expected-error@+2 {{cannot redeclare builtin function '__builtin_va_end'}}
 // expected-note@+1 {{'__builtin_va_end' is a builtin with type}}
 void __builtin_va_end(__builtin_va_list);
-// RUN: %clang_cc1 %s -fsyntax-only -verify 
-// RUN: %clang_cc1 %s -fsyntax-only -verify -x c
 
 void __va_start(__builtin_va_list*, ...);
 
+  void *__builtin_assume_aligned(const void *, size_t, ...);
 #ifdef __cplusplus
-void *__builtin_assume_aligned(const void *, size_t, ...) noexcept;
-#else
-void *__builtin_assume_aligned(const void *, size_t, ...);
+constexpr void *__builtin_assume_aligned(const void *, size_t, ...);
+  void *__builtin_assume_aligned(const void *, size_t, ...) noexcept;
+constexpr void *__builtin_assume_aligned(const void *, size_t, ...) noexcept;
+  void *__builtin_assume_aligned(const void *, size_t, ...) throw();
+constexpr void *__builtin_assume_aligned(const void *, size_t, ...) throw();
+

MitalAshok wrote:

That seems like that should go in a separate patch. For now, I'll change this 
one so `ConstexprSpecKind::Constexpr` isn't added to these builtins as before

https://github.com/llvm/llvm-project/pull/91894
___
cfe-commits mailing list
cfe-commits@lists.llvm.org
https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits

[clang] [Clang] Add attribute for consteval builtins; Declare constexpr builtins as constexpr in C++ (PR #91894)

[Erich Keane via cfe-commits]

@@ -14,13 +14,18 @@ void __builtin_va_copy(double d);
 // expected-error@+2 {{cannot redeclare builtin function '__builtin_va_end'}}
 // expected-note@+1 {{'__builtin_va_end' is a builtin with type}}
 void __builtin_va_end(__builtin_va_list);
-// RUN: %clang_cc1 %s -fsyntax-only -verify 
-// RUN: %clang_cc1 %s -fsyntax-only -verify -x c
 
 void __va_start(__builtin_va_list*, ...);
 
+  void *__builtin_assume_aligned(const void *, size_t, ...);
 #ifdef __cplusplus
-void *__builtin_assume_aligned(const void *, size_t, ...) noexcept;
-#else
-void *__builtin_assume_aligned(const void *, size_t, ...);
+constexpr void *__builtin_assume_aligned(const void *, size_t, ...);
+  void *__builtin_assume_aligned(const void *, size_t, ...) noexcept;
+constexpr void *__builtin_assume_aligned(const void *, size_t, ...) noexcept;
+  void *__builtin_assume_aligned(const void *, size_t, ...) throw();
+constexpr void *__builtin_assume_aligned(const void *, size_t, ...) throw();
+

erichkeane wrote:

>From reading through that (and trying to search my memory): A number of our 
>`LIBBUILTIN` builtins are just replacements for things that would otherwise be 
>implemented in the  library.  

So we need to allow them to be redeclared because they might be implemented in 
the library.

However, I would be unopposed to a patch that makes declaring a `__builtin` 
spelled as  reserved identifier ill-formed.

https://github.com/llvm/llvm-project/pull/91894
___
cfe-commits mailing list
cfe-commits@lists.llvm.org
https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits

[clang] [Clang] Add attribute for consteval builtins; Declare constexpr builtins as constexpr in C++ (PR #91894)

[via cfe-commits]

@@ -14,13 +14,18 @@ void __builtin_va_copy(double d);
 // expected-error@+2 {{cannot redeclare builtin function '__builtin_va_end'}}
 // expected-note@+1 {{'__builtin_va_end' is a builtin with type}}
 void __builtin_va_end(__builtin_va_list);
-// RUN: %clang_cc1 %s -fsyntax-only -verify 
-// RUN: %clang_cc1 %s -fsyntax-only -verify -x c
 
 void __va_start(__builtin_va_list*, ...);
 
+  void *__builtin_assume_aligned(const void *, size_t, ...);
 #ifdef __cplusplus
-void *__builtin_assume_aligned(const void *, size_t, ...) noexcept;
-#else
-void *__builtin_assume_aligned(const void *, size_t, ...);
+constexpr void *__builtin_assume_aligned(const void *, size_t, ...);
+  void *__builtin_assume_aligned(const void *, size_t, ...) noexcept;
+constexpr void *__builtin_assume_aligned(const void *, size_t, ...) noexcept;
+  void *__builtin_assume_aligned(const void *, size_t, ...) throw();
+constexpr void *__builtin_assume_aligned(const void *, size_t, ...) throw();
+

cor3ntin wrote:

@erichkeane 

https://github.com/llvm/llvm-project/pull/91894
___
cfe-commits mailing list
cfe-commits@lists.llvm.org
https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits

[clang] [Clang] Add attribute for consteval builtins; Declare constexpr builtins as constexpr in C++ (PR #91894)

[Richard Smith via cfe-commits]

@@ -14,13 +14,18 @@ void __builtin_va_copy(double d);
 // expected-error@+2 {{cannot redeclare builtin function '__builtin_va_end'}}
 // expected-note@+1 {{'__builtin_va_end' is a builtin with type}}
 void __builtin_va_end(__builtin_va_list);
-// RUN: %clang_cc1 %s -fsyntax-only -verify 
-// RUN: %clang_cc1 %s -fsyntax-only -verify -x c
 
 void __va_start(__builtin_va_list*, ...);
 
+  void *__builtin_assume_aligned(const void *, size_t, ...);
 #ifdef __cplusplus
-void *__builtin_assume_aligned(const void *, size_t, ...) noexcept;
-#else
-void *__builtin_assume_aligned(const void *, size_t, ...);
+constexpr void *__builtin_assume_aligned(const void *, size_t, ...);
+  void *__builtin_assume_aligned(const void *, size_t, ...) noexcept;
+constexpr void *__builtin_assume_aligned(const void *, size_t, ...) noexcept;
+  void *__builtin_assume_aligned(const void *, size_t, ...) throw();
+constexpr void *__builtin_assume_aligned(const void *, size_t, ...) throw();
+

zygoloid wrote:

I don't think there are particularly good non-historical reasons why we allow 
non-`LIBBUILTIN` builtins to be redeclared -- I think it's allowed primarily 
for compatibility with GCC and existing code, and it's not clear to me why GCC 
allows it. There were some examples of code redeclaring builtins in [this prior 
review thread](https://reviews.llvm.org/D45383).

https://github.com/llvm/llvm-project/pull/91894
___
cfe-commits mailing list
cfe-commits@lists.llvm.org
https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits

[clang] [Clang] Add attribute for consteval builtins; Declare constexpr builtins as constexpr in C++ (PR #91894)

[via cfe-commits]

https://github.com/cor3ntin edited 
https://github.com/llvm/llvm-project/pull/91894
___
cfe-commits mailing list
cfe-commits@lists.llvm.org
https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits

[clang] [Clang] Add attribute for consteval builtins; Declare constexpr builtins as constexpr in C++ (PR #91894)

[Aaron Ballman via cfe-commits]

@@ -14,13 +14,18 @@ void __builtin_va_copy(double d);
 // expected-error@+2 {{cannot redeclare builtin function '__builtin_va_end'}}
 // expected-note@+1 {{'__builtin_va_end' is a builtin with type}}
 void __builtin_va_end(__builtin_va_list);
-// RUN: %clang_cc1 %s -fsyntax-only -verify 
-// RUN: %clang_cc1 %s -fsyntax-only -verify -x c
 
 void __va_start(__builtin_va_list*, ...);
 
+  void *__builtin_assume_aligned(const void *, size_t, ...);
 #ifdef __cplusplus
-void *__builtin_assume_aligned(const void *, size_t, ...) noexcept;
-#else
-void *__builtin_assume_aligned(const void *, size_t, ...);
+constexpr void *__builtin_assume_aligned(const void *, size_t, ...);
+  void *__builtin_assume_aligned(const void *, size_t, ...) noexcept;
+constexpr void *__builtin_assume_aligned(const void *, size_t, ...) noexcept;
+  void *__builtin_assume_aligned(const void *, size_t, ...) throw();
+constexpr void *__builtin_assume_aligned(const void *, size_t, ...) throw();
+

AaronBallman wrote:

Does anyone know why we allow builtins to be redeclared at all? CC @zygoloid 
@rjmccall 

I wonder just how much code we would break by not aiming for backwards 
compatibility here and requiring users to update their declarations on the 
assumption that declaring these at all is undefined behavior (using a reserved 
name) and so it's up to the user to match the compiler's behavior rather than 
make the compiler handle this with weird non-conforming language extension 
behavior.

I'm not looking to punish users in this case, but the workaround to keep things 
backwards compatible is pretty magical and awkward.

https://github.com/llvm/llvm-project/pull/91894
___
cfe-commits mailing list
cfe-commits@lists.llvm.org
https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits

[clang] [Clang] Add attribute for consteval builtins; Declare constexpr builtins as constexpr in C++ (PR #91894)

[Mital Ashok via cfe-commits]

@@ -14,13 +14,18 @@ void __builtin_va_copy(double d);
 // expected-error@+2 {{cannot redeclare builtin function '__builtin_va_end'}}
 // expected-note@+1 {{'__builtin_va_end' is a builtin with type}}
 void __builtin_va_end(__builtin_va_list);
-// RUN: %clang_cc1 %s -fsyntax-only -verify 
-// RUN: %clang_cc1 %s -fsyntax-only -verify -x c
 
 void __va_start(__builtin_va_list*, ...);
 
+  void *__builtin_assume_aligned(const void *, size_t, ...);
 #ifdef __cplusplus
-void *__builtin_assume_aligned(const void *, size_t, ...) noexcept;
-#else
-void *__builtin_assume_aligned(const void *, size_t, ...);
+constexpr void *__builtin_assume_aligned(const void *, size_t, ...);
+  void *__builtin_assume_aligned(const void *, size_t, ...) noexcept;
+constexpr void *__builtin_assume_aligned(const void *, size_t, ...) noexcept;
+  void *__builtin_assume_aligned(const void *, size_t, ...) throw();
+constexpr void *__builtin_assume_aligned(const void *, size_t, ...) throw();
+

MitalAshok wrote:

For backwards compatibility (and compatibility with the same definitions in C 
or with GCC), to allow declarations with or without the `constexpr`. I suspect 
in any real code, it will always be declared without the `constexpr`.

The other solutions is to keep them all as `ConstexprSpecKind::Unspecified` 
like we currently do, but this is asymmetric with `consteval` builtins which 
will be marked `ConstexprSpecKind::Consteval`, and leads to the builtin 
versions of `std::move`/`std::forward`/constexpr cmath functions to have 
differing `getConstexprKind()` from their non-builtin counterparts



https://github.com/llvm/llvm-project/pull/91894
___
cfe-commits mailing list
cfe-commits@lists.llvm.org
https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits

[clang] [Clang] Add attribute for consteval builtins; Declare constexpr builtins as constexpr in C++ (PR #91894)

[via cfe-commits]

@@ -14,13 +14,18 @@ void __builtin_va_copy(double d);
 // expected-error@+2 {{cannot redeclare builtin function '__builtin_va_end'}}
 // expected-note@+1 {{'__builtin_va_end' is a builtin with type}}
 void __builtin_va_end(__builtin_va_list);
-// RUN: %clang_cc1 %s -fsyntax-only -verify 
-// RUN: %clang_cc1 %s -fsyntax-only -verify -x c
 
 void __va_start(__builtin_va_list*, ...);
 
+  void *__builtin_assume_aligned(const void *, size_t, ...);
 #ifdef __cplusplus
-void *__builtin_assume_aligned(const void *, size_t, ...) noexcept;
-#else
-void *__builtin_assume_aligned(const void *, size_t, ...);
+constexpr void *__builtin_assume_aligned(const void *, size_t, ...);
+  void *__builtin_assume_aligned(const void *, size_t, ...) noexcept;
+constexpr void *__builtin_assume_aligned(const void *, size_t, ...) noexcept;
+  void *__builtin_assume_aligned(const void *, size_t, ...) throw();
+constexpr void *__builtin_assume_aligned(const void *, size_t, ...) throw();
+

cor3ntin wrote:

What is the motivation to allow that?

I kind of understand letting users defining builtin (actually, I am not sure I 
do). but once the builtin is redefined once, I think should be some sort of 
consistency with the language rules.
Here if you were to replace `__builtin_assume_aligned` with `f`, it would be 
ill-formed, for god reason.

https://github.com/llvm/llvm-project/pull/91894
___
cfe-commits mailing list
cfe-commits@lists.llvm.org
https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits

[clang] [Clang] Add attribute for consteval builtins; Declare constexpr builtins as constexpr in C++ (PR #91894)

[Mital Ashok via cfe-commits]

MitalAshok wrote:

Currently, GCC's behaviour for builtin function redeclarations is to just 
ignore `constexpr`: . This is slightly 
stricter, allowing non-`constexpr` redeclarations for `constexpr` builtins but 
still disallowing `constexpr` declarations for non-`constexpr` builtins.

[P2641R4 `std::is_within_lifetime`](https://wg21.link/P2641R4) is most likely 
going to be implemented as a `consteval` builtin, which the attribute allows 
implementing easily as a builtin-function with `getConstexprKind() == 
ConstexprSpecKind::Consteval`.

https://github.com/llvm/llvm-project/pull/91894
___
cfe-commits mailing list
cfe-commits@lists.llvm.org
https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits

[clang] [Clang] Add attribute for consteval builtins; Declare constexpr builtins as constexpr in C++ (PR #91894)

[via cfe-commits]

llvmbot wrote:




@llvm/pr-subscribers-clang

Author: Mital Ashok (MitalAshok)


Changes

Also support redeclaring now-constexpr builtins without constexpr

---
Full diff: https://github.com/llvm/llvm-project/pull/91894.diff


6 Files Affected:

- (modified) clang/include/clang/Basic/Builtins.h (+5) 
- (modified) clang/include/clang/Basic/BuiltinsBase.td (+2) 
- (modified) clang/lib/Sema/SemaDecl.cpp (+11-4) 
- (modified) clang/lib/Sema/SemaDeclCXX.cpp (+13-5) 
- (modified) clang/lib/Sema/SemaExpr.cpp (+6-2) 
- (modified) clang/test/Sema/builtin-redecl.cpp (+10-5) 


``diff
diff --git a/clang/include/clang/Basic/Builtins.h 
b/clang/include/clang/Basic/Builtins.h
index f955d21169556..e85ec5b2dca14 100644
--- a/clang/include/clang/Basic/Builtins.h
+++ b/clang/include/clang/Basic/Builtins.h
@@ -280,6 +280,11 @@ class Context {
 return strchr(getRecord(ID).Attributes, 'E') != nullptr;
   }
 
+  /// Returns true if this is an immediate (consteval) function
+  bool isImmediate(unsigned ID) const {
+return strchr(getRecord(ID).Attributes, 'G') != nullptr;
+  }
+
 private:
   const Info (unsigned ID) const;
 
diff --git a/clang/include/clang/Basic/BuiltinsBase.td 
b/clang/include/clang/Basic/BuiltinsBase.td
index 724747ec76d73..1196b9e15c10d 100644
--- a/clang/include/clang/Basic/BuiltinsBase.td
+++ b/clang/include/clang/Basic/BuiltinsBase.td
@@ -70,6 +70,8 @@ class VScanfFormat : IndexedAttribute<"S", I>;
 
 // Builtin can be constant evaluated
 def Constexpr : Attribute<"E">;
+// Builtin is immediate and must be constant evaluated. Implies Constexpr.
+def Consteval : Attribute<"EG">;
 
 // Builtin kinds
 // =
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index fb913034bd836..6b0a04585928a 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -2409,10 +2409,17 @@ FunctionDecl *Sema::CreateBuiltin(IdentifierInfo *II, 
QualType Type,
 Parent = CLinkageDecl;
   }
 
-  FunctionDecl *New = FunctionDecl::Create(Context, Parent, Loc, Loc, II, Type,
-   /*TInfo=*/nullptr, SC_Extern,
-   
getCurFPFeatures().isFPConstrained(),
-   false, Type->isFunctionProtoType());
+  ConstexprSpecKind ConstexprKind = ConstexprSpecKind::Unspecified;
+  if (getLangOpts().CPlusPlus && Context.BuiltinInfo.isConstantEvaluated(ID)) {
+ConstexprKind = ConstexprSpecKind::Constexpr;
+if (Context.BuiltinInfo.isImmediate(ID))
+  ConstexprKind = ConstexprSpecKind::Consteval;
+  }
+
+  FunctionDecl *New = FunctionDecl::Create(
+  Context, Parent, Loc, Loc, II, Type, /*TInfo=*/nullptr, SC_Extern,
+  getCurFPFeatures().isFPConstrained(), /*isInlineSpecified=*/false,
+  Type->isFunctionProtoType(), ConstexprKind);
   New->setImplicit();
   New->addAttr(BuiltinAttr::CreateImplicit(Context, ID));
 
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index 53238d355ea09..1b558d70f9b48 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -676,11 +676,19 @@ bool Sema::MergeCXXFunctionDecl(FunctionDecl *New, 
FunctionDecl *Old,
   // template has a constexpr specifier then all its declarations shall
   // contain the constexpr specifier.
   if (New->getConstexprKind() != Old->getConstexprKind()) {
-Diag(New->getLocation(), diag::err_constexpr_redecl_mismatch)
-<< New << static_cast(New->getConstexprKind())
-<< static_cast(Old->getConstexprKind());
-Diag(Old->getLocation(), diag::note_previous_declaration);
-Invalid = true;
+if (Old->getBuiltinID() &&
+Old->getConstexprKind() == ConstexprSpecKind::Constexpr &&
+New->getConstexprKind() == ConstexprSpecKind::Unspecified) {
+  // Except allow redeclaring a builtin as non-constexpr to match C
+  // redeclarations which will not be constexpr
+  New->setConstexprKind(ConstexprSpecKind::Constexpr);
+} else {
+  Diag(New->getLocation(), diag::err_constexpr_redecl_mismatch)
+  << New << static_cast(New->getConstexprKind())
+  << static_cast(Old->getConstexprKind());
+  Diag(Old->getLocation(), diag::note_previous_declaration);
+  Invalid = true;
+}
   } else if (!Old->getMostRecentDecl()->isInlined() && New->isInlined() &&
  Old->isDefined(Def) &&
  // If a friend function is inlined but does not have 'inline'
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index bb4b116fd73ca..39aa32526d2b1 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -7095,8 +7095,12 @@ ExprResult Sema::BuildResolvedCallExpr(Expr *Fn, 
NamedDecl *NDecl,
   }
 
   // Bail out early if calling a builtin with custom type checking.
-  if (BuiltinID && Context.BuiltinInfo.hasCustomTypechecking(BuiltinID))
-return CheckBuiltinFunctionCall(FDecl, BuiltinID, TheCall);
+  if (BuiltinID && 

[clang] [Clang] Add attribute for consteval builtins; Declare constexpr builtins as constexpr in C++ (PR #91894)

[Mital Ashok via cfe-commits]

https://github.com/MitalAshok created 
https://github.com/llvm/llvm-project/pull/91894

Also support redeclaring now-constexpr builtins without constexpr

>From 56aed689dc5825fc5bacc6dfdff58ee0eaf71f82 Mon Sep 17 00:00:00 2001
From: Mital Ashok 
Date: Sun, 12 May 2024 19:48:24 +0100
Subject: [PATCH] [Clang] Add attribute for consteval builtins; Declare
 constexpr builtins as constexpr in C++

Also support redeclaring now-constexpr builtins without constexpr
---
 clang/include/clang/Basic/Builtins.h  |  5 +
 clang/include/clang/Basic/BuiltinsBase.td |  2 ++
 clang/lib/Sema/SemaDecl.cpp   | 15 +++
 clang/lib/Sema/SemaDeclCXX.cpp| 18 +-
 clang/lib/Sema/SemaExpr.cpp   |  8 ++--
 clang/test/Sema/builtin-redecl.cpp| 15 ++-
 6 files changed, 47 insertions(+), 16 deletions(-)

diff --git a/clang/include/clang/Basic/Builtins.h 
b/clang/include/clang/Basic/Builtins.h
index f955d21169556..e85ec5b2dca14 100644
--- a/clang/include/clang/Basic/Builtins.h
+++ b/clang/include/clang/Basic/Builtins.h
@@ -280,6 +280,11 @@ class Context {
 return strchr(getRecord(ID).Attributes, 'E') != nullptr;
   }
 
+  /// Returns true if this is an immediate (consteval) function
+  bool isImmediate(unsigned ID) const {
+return strchr(getRecord(ID).Attributes, 'G') != nullptr;
+  }
+
 private:
   const Info (unsigned ID) const;
 
diff --git a/clang/include/clang/Basic/BuiltinsBase.td 
b/clang/include/clang/Basic/BuiltinsBase.td
index 724747ec76d73..1196b9e15c10d 100644
--- a/clang/include/clang/Basic/BuiltinsBase.td
+++ b/clang/include/clang/Basic/BuiltinsBase.td
@@ -70,6 +70,8 @@ class VScanfFormat : IndexedAttribute<"S", I>;
 
 // Builtin can be constant evaluated
 def Constexpr : Attribute<"E">;
+// Builtin is immediate and must be constant evaluated. Implies Constexpr.
+def Consteval : Attribute<"EG">;
 
 // Builtin kinds
 // =
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index fb913034bd836..6b0a04585928a 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -2409,10 +2409,17 @@ FunctionDecl *Sema::CreateBuiltin(IdentifierInfo *II, 
QualType Type,
 Parent = CLinkageDecl;
   }
 
-  FunctionDecl *New = FunctionDecl::Create(Context, Parent, Loc, Loc, II, Type,
-   /*TInfo=*/nullptr, SC_Extern,
-   
getCurFPFeatures().isFPConstrained(),
-   false, Type->isFunctionProtoType());
+  ConstexprSpecKind ConstexprKind = ConstexprSpecKind::Unspecified;
+  if (getLangOpts().CPlusPlus && Context.BuiltinInfo.isConstantEvaluated(ID)) {
+ConstexprKind = ConstexprSpecKind::Constexpr;
+if (Context.BuiltinInfo.isImmediate(ID))
+  ConstexprKind = ConstexprSpecKind::Consteval;
+  }
+
+  FunctionDecl *New = FunctionDecl::Create(
+  Context, Parent, Loc, Loc, II, Type, /*TInfo=*/nullptr, SC_Extern,
+  getCurFPFeatures().isFPConstrained(), /*isInlineSpecified=*/false,
+  Type->isFunctionProtoType(), ConstexprKind);
   New->setImplicit();
   New->addAttr(BuiltinAttr::CreateImplicit(Context, ID));
 
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index 53238d355ea09..1b558d70f9b48 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -676,11 +676,19 @@ bool Sema::MergeCXXFunctionDecl(FunctionDecl *New, 
FunctionDecl *Old,
   // template has a constexpr specifier then all its declarations shall
   // contain the constexpr specifier.
   if (New->getConstexprKind() != Old->getConstexprKind()) {
-Diag(New->getLocation(), diag::err_constexpr_redecl_mismatch)
-<< New << static_cast(New->getConstexprKind())
-<< static_cast(Old->getConstexprKind());
-Diag(Old->getLocation(), diag::note_previous_declaration);
-Invalid = true;
+if (Old->getBuiltinID() &&
+Old->getConstexprKind() == ConstexprSpecKind::Constexpr &&
+New->getConstexprKind() == ConstexprSpecKind::Unspecified) {
+  // Except allow redeclaring a builtin as non-constexpr to match C
+  // redeclarations which will not be constexpr
+  New->setConstexprKind(ConstexprSpecKind::Constexpr);
+} else {
+  Diag(New->getLocation(), diag::err_constexpr_redecl_mismatch)
+  << New << static_cast(New->getConstexprKind())
+  << static_cast(Old->getConstexprKind());
+  Diag(Old->getLocation(), diag::note_previous_declaration);
+  Invalid = true;
+}
   } else if (!Old->getMostRecentDecl()->isInlined() && New->isInlined() &&
  Old->isDefined(Def) &&
  // If a friend function is inlined but does not have 'inline'
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index bb4b116fd73ca..39aa32526d2b1 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -7095,8 +7095,12 @@ ExprResult