[clang] [clang] __is_trivially_equality_comparable for types containing lambdas (PR #68506)

[Amirreza Ashouri via cfe-commits]

https://github.com/AMP999 updated https://github.com/llvm/llvm-project/pull/68506

>From fdbeba9c94ddb13ee53a761d9e1a95b044f2c20a Mon Sep 17 00:00:00 2001
From: Amirreza Ashouri <ar.ashouri999 at gmail.com>
Date: Sat, 7 Oct 2023 19:02:34 +0330
Subject: [PATCH 1/3] [clang] Rename some misleading names (Non-functional)
 These names could be misleading; should we change them to
 `NonTriviallyComparable` instead?

---
 clang/test/SemaCXX/type-traits.cpp | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/clang/test/SemaCXX/type-traits.cpp b/clang/test/SemaCXX/type-traits.cpp
index a35689d52978fcc..a1315f1966a6dd4 100644
--- a/clang/test/SemaCXX/type-traits.cpp
+++ b/clang/test/SemaCXX/type-traits.cpp
@@ -3160,11 +3160,18 @@ static_assert(!__is_trivially_equality_comparable(float), "");
 static_assert(!__is_trivially_equality_comparable(double), "");
 static_assert(!__is_trivially_equality_comparable(long double), "");
 
-struct TriviallyEqualityComparableNoDefaultedComparator {
+struct NonTriviallyEqualityComparableNoComparator {
   int i;
   int j;
 };
-static_assert(!__is_trivially_equality_comparable(TriviallyEqualityComparableNoDefaultedComparator), "");
+static_assert(!__is_trivially_equality_comparable(NonTriviallyEqualityComparableNoComparator), "");
+
+struct NonTriviallyEqualityComparableNonDefaultedComparator {
+  int i;
+  int j;
+  bool operator==(const NonTriviallyEqualityComparableNonDefaultedComparator&);
+};
+static_assert(!__is_trivially_equality_comparable(NonTriviallyEqualityComparableNonDefaultedComparator), "");
 
 #if __cplusplus >= 202002L
 
@@ -3177,7 +3184,7 @@ struct TriviallyEqualityComparable {
 
   bool operator==(const TriviallyEqualityComparable&) const = default;
 };
-static_assert(__is_trivially_equality_comparable(TriviallyEqualityComparable), "");
+static_assert(__is_trivially_equality_comparable(TriviallyEqualityComparable));
 
 struct TriviallyEqualityComparableContainsArray {
   int a[4];

>From 5820c4e478c035a65512994f354df081266467dc Mon Sep 17 00:00:00 2001
From: Amirreza Ashouri <ar.ashouri999 at gmail.com>
Date: Sun, 8 Oct 2023 18:00:51 +0330
Subject: [PATCH 2/3] [clang] __is_trivially_equality_comparable for types
 containing lambdas

Lambdas (closure types) are trivially equality-comparable iff they are
non-capturing, because non-capturing lambdas are convertible to function
pointers: if `(lam1 == lam2)` compiles, then `lam1` and `lam2` must have
the same type, and be always-equal, and be empty.
---
 clang/lib/AST/Type.cpp             |  3 +++
 clang/test/SemaCXX/type-traits.cpp | 11 +++++++++++
 2 files changed, 14 insertions(+)

diff --git a/clang/lib/AST/Type.cpp b/clang/lib/AST/Type.cpp
index 4c433f7fe9daca0..23f856c715a5e13 100644
--- a/clang/lib/AST/Type.cpp
+++ b/clang/lib/AST/Type.cpp
@@ -2663,6 +2663,9 @@ static bool
 HasNonDeletedDefaultedEqualityComparison(const CXXRecordDecl *Decl) {
   if (Decl->isUnion())
     return false;
+  if (Decl->isLambda())
+    return Decl->captures().empty() &&
+           (Decl->getLambdaCaptureDefault() == LCD_None);
 
   auto IsDefaultedOperatorEqualEqual = [&](const FunctionDecl *Function) {
     return Function->getOverloadedOperator() ==
diff --git a/clang/test/SemaCXX/type-traits.cpp b/clang/test/SemaCXX/type-traits.cpp
index a1315f1966a6dd4..275ddcbae73930d 100644
--- a/clang/test/SemaCXX/type-traits.cpp
+++ b/clang/test/SemaCXX/type-traits.cpp
@@ -3200,6 +3200,17 @@ struct TriviallyEqualityComparableContainsMultiDimensionArray {
 };
 static_assert(__is_trivially_equality_comparable(TriviallyEqualityComparableContainsMultiDimensionArray));
 
+auto GetNonCapturingLambda() { return [](){ return 42; }; }
+
+struct TriviallyEqualityComparableContainsLambda {
+  [[no_unique_address]] decltype(GetNonCapturingLambda()) l;
+  int i;
+
+  bool operator==(const TriviallyEqualityComparableContainsLambda&) const = default;
+};
+static_assert(!__is_trivially_equality_comparable(decltype(GetNonCapturingLambda()))); // padding
+static_assert(__is_trivially_equality_comparable(TriviallyEqualityComparableContainsLambda));
+
 struct TriviallyEqualityComparableNonTriviallyCopyable {
   TriviallyEqualityComparableNonTriviallyCopyable(const TriviallyEqualityComparableNonTriviallyCopyable&);
   ~TriviallyEqualityComparableNonTriviallyCopyable();

>From edd82edc6dd1ca1a143b4e667d5e4a30d8e7a1d4 Mon Sep 17 00:00:00 2001
From: Arthur O'Dwyer <arthur.j.odwyer at gmail.com>
Date: Tue, 10 Oct 2023 10:03:17 -0400
Subject: [PATCH 3/3] [clang] Factor out isCapturelessLambda

This changes the behavior of the call-site in "CodeGenFunction.cpp",
I think for the better. But I couldn't figure out how to test that
codepath.
---
 clang/include/clang/AST/DeclCXX.h     | 6 ++++++
 clang/lib/AST/DeclCXX.cpp             | 2 +-
 clang/lib/AST/Type.cpp                | 3 +--
 clang/lib/CodeGen/CodeGenFunction.cpp | 5 ++---
 clang/lib/Sema/SemaLambda.cpp         | 3 +--
 5 files changed, 11 insertions(+), 8 deletions(-)

diff --git a/clang/include/clang/AST/DeclCXX.h b/clang/include/clang/AST/DeclCXX.h
index aa3e3322faa42e3..5eaae6bdd2bc63e 100644
--- a/clang/include/clang/AST/DeclCXX.h
+++ b/clang/include/clang/AST/DeclCXX.h
@@ -1052,6 +1052,12 @@ class CXXRecordDecl : public RecordDecl {
     return static_cast<LambdaCaptureDefault>(getLambdaData().CaptureDefault);
   }
 
+  bool isCapturelessLambda() const {
+    if (!isLambda())
+      return false;
+    return getLambdaCaptureDefault() == LCD_None && capture_size() == 0;
+  }
+
   /// Set the captures for this lambda closure type.
   void setCaptures(ASTContext &Context, ArrayRef<LambdaCapture> Captures);
 
diff --git a/clang/lib/AST/DeclCXX.cpp b/clang/lib/AST/DeclCXX.cpp
index a92b788366434ce..9107525a44f22c2 100644
--- a/clang/lib/AST/DeclCXX.cpp
+++ b/clang/lib/AST/DeclCXX.cpp
@@ -686,7 +686,7 @@ bool CXXRecordDecl::lambdaIsDefaultConstructibleAndAssignable() const {
   // C++17 [expr.prim.lambda]p21:
   //   The closure type associated with a lambda-expression has no default
   //   constructor and a deleted copy assignment operator.
-  if (getLambdaCaptureDefault() != LCD_None || capture_size() != 0)
+  if (!isCapturelessLambda())
     return false;
   return getASTContext().getLangOpts().CPlusPlus20;
 }
diff --git a/clang/lib/AST/Type.cpp b/clang/lib/AST/Type.cpp
index 23f856c715a5e13..282298971705ba0 100644
--- a/clang/lib/AST/Type.cpp
+++ b/clang/lib/AST/Type.cpp
@@ -2664,8 +2664,7 @@ HasNonDeletedDefaultedEqualityComparison(const CXXRecordDecl *Decl) {
   if (Decl->isUnion())
     return false;
   if (Decl->isLambda())
-    return Decl->captures().empty() &&
-           (Decl->getLambdaCaptureDefault() == LCD_None);
+    return Decl->isCapturelessLambda();
 
   auto IsDefaultedOperatorEqualEqual = [&](const FunctionDecl *Function) {
     return Function->getOverloadedOperator() ==
diff --git a/clang/lib/CodeGen/CodeGenFunction.cpp b/clang/lib/CodeGen/CodeGenFunction.cpp
index 9b21f428b0af7f5..42777194cc76dc0 100644
--- a/clang/lib/CodeGen/CodeGenFunction.cpp
+++ b/clang/lib/CodeGen/CodeGenFunction.cpp
@@ -1216,11 +1216,10 @@ void CodeGenFunction::StartFunction(GlobalDecl GD, QualType RetTy,
       SkippedChecks.set(SanitizerKind::ObjectSize, true);
       QualType ThisTy = MD->getThisType();
 
-      // If this is the call operator of a lambda with no capture-default, it
+      // If this is the call operator of a lambda with no captures, it
       // may have a static invoker function, which may call this operator with
       // a null 'this' pointer.
-      if (isLambdaCallOperator(MD) &&
-          MD->getParent()->getLambdaCaptureDefault() == LCD_None)
+      if (isLambdaCallOperator(MD) && MD->getParent()->isCapturelessLambda())
         SkippedChecks.set(SanitizerKind::Null, true);
 
       EmitTypeCheck(
diff --git a/clang/lib/Sema/SemaLambda.cpp b/clang/lib/Sema/SemaLambda.cpp
index 421048aaff5c90c..ca09b0481bcac76 100644
--- a/clang/lib/Sema/SemaLambda.cpp
+++ b/clang/lib/Sema/SemaLambda.cpp
@@ -393,8 +393,7 @@ void Sema::DiagnoseInvalidExplicitObjectParameterInLambda(
   CXXRecordDecl *RD = Method->getParent();
   if (Method->getType()->isDependentType())
     return;
-  if (RD->getLambdaCaptureDefault() == LambdaCaptureDefault::LCD_None &&
-      RD->capture_size() == 0)
+  if (RD->isCapturelessLambda())
     return;
   QualType ExplicitObjectParameterType = Method->getParamDecl(0)
                                              ->getType()