[Clang] Fix defaulted equality operator so that it does not attempt to compare unnamed bit-fields

[shafik]

Summary

If we look at class.bit p2 it tells us that that unnamed bit-fields are not members and class.compare.default p5 tells us that we should only non-static data members of the class.

This fixes: https://github.com/llvm/llvm-project/issues/61335 and https://github.com/llvm/llvm-project/issues/61417

[shafik]

I would have loved to test the case from https://github.com/llvm/llvm-project/issues/61335 directly but I think in order to do it nicely I need __builtin_memset to be usable in a constant expression context. I will add this to my todo list. I am open to other alternatives for testing this.

[royjacobson]

In D146329#4203174, @shafik wrote:

I would have loved to test the case from https://github.com/llvm/llvm-project/issues/61335 directly but I think in order to do it nicely I need __builtin_memset to be usable in a constant expression context. I will add this to my todo list. I am open to other alternatives for testing this.

I managed to generate relatively readable LLVM IR for this: https://godbolt.org/z/z1YzoEcr3 (the generated equality operators are obviously not correct yet), I think matching against that is testing the issue pretty well.

(The trick to making it readable was turning on optimization, though. Not sure if we usually do that)

[shafik]

In D146329#4207522, @royjacobson wrote:

In D146329#4203174, @shafik wrote:

I would have loved to test the case from https://github.com/llvm/llvm-project/issues/61335 directly but I think in order to do it nicely I need __builtin_memset to be usable in a constant expression context. I will add this to my todo list. I am open to other alternatives for testing this.

I managed to generate relatively readable LLVM IR for this: https://godbolt.org/z/z1YzoEcr3 (the generated equality operators are obviously not correct yet), I think matching against that is testing the issue pretty well.

(The trick to making it readable was turning on optimization, though. Not sure if we usually do that)

I think in general we can't rely on optimizations in test like this but wdyt @erichkeane

[erichkeane]

In D146329#4242215, @shafik wrote:

In D146329#4207522, @royjacobson wrote:

In D146329#4203174, @shafik wrote:

I would have loved to test the case from https://github.com/llvm/llvm-project/issues/61335 directly but I think in order to do it nicely I need __builtin_memset to be usable in a constant expression context. I will add this to my todo list. I am open to other alternatives for testing this.

I managed to generate relatively readable LLVM IR for this: https://godbolt.org/z/z1YzoEcr3 (the generated equality operators are obviously not correct yet), I think matching against that is testing the issue pretty well.

(The trick to making it readable was turning on optimization, though. Not sure if we usually do that)

I think in general we can't rely on optimizations in test like this but wdyt @erichkeane

We should not have opt enabled in our lit tests, thats correct. However, the non-optimized version of that godbolt link has reasonably readable IR that we can test.

[shafik]

• Added codegen test

[shafik]

@erichkeane let me know if the test I added is sufficient

[erichkeane]

clang/test/CodeGenCXX/defaulted_equality_ignore_unnamed_bitfields.cpp

24

I think these check lines aren't nearly specific enough, i think it should have a handful of CHECK lines confirming what we're doing, not just what we're not.

[shafik]

• Update codegen test based on feedback

[shafik]

• Add release note

clang/docs/ReleaseNotes.rst

 - Fix crash when a doc comment contains a line splicing.
   (`#62054 <https://github.com/llvm/llvm-project/issues/62054>`_)
 - Work around with a clang coverage crash which happens when visiting 
   expressions/statements with invalid source locations in non-assert builds. 
   Assert builds may still see assertions triggered from this.
 - Fix a failed assertion due to an invalid source location when trying to form
   a coverage report for an unresolved constructor expression.
   (`#62105 <https://github.com/llvm/llvm-project/issues/62105>`_)
+- Fix defaulted equality operator so that it does not attempt to compare unnamed
+  bit-fields. This fixes:
+  (`#61355 <https://github.com/llvm/llvm-project/issues/61335>`_) and
+  (`#61417 <https://github.com/llvm/llvm-project/issues/61417>`_)
 
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 Bug Fixes to Attribute Support
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 Bug Fixes to C++ Support

clang/lib/Sema/SemaDeclCXX.cpp

bool visitSubobjects(ResultList &Results, CXXRecordDecl *Record,
     for (CXXBaseSpecifier &Base : Record->bases())
       if (Results.add(getDerived().visitSubobject(
               S.Context.getQualifiedType(Base.getType(), Quals),
               getDerived().getBase(&Base))))
         return true;
 
     //   followed by the non-static data members of C
     for (FieldDecl *Field : Record->fields()) {
+      // C++23 [class.bit]p2:
+      //   Unnamed bit-fields are not members ...
+      if (Field->isUnnamedBitfield())
+        continue;
       // Recursively expand anonymous structs.
       if (Field->isAnonymousStructOrUnion()) {
         if (visitSubobjects(Results, Field->getType()->getAsCXXRecordDecl(),
                             Quals))
           return true;
         continue;
       }
 

clang/test/CXX/class/class.compare/class.compare.default/p1.cpp

 
 void f2() {
   S7<int> a; // expected-note{{S7<int>' requested}}
   S7<evil> b;
   (void)(a == 0); // expected-error{{invalid operands}}
   (void)(b == 0);
 }
 } // namespace p2085_2
+
+namespace GH61417 {
+struct A {
+  unsigned x : 1;
+  unsigned   : 0;
+  unsigned y : 1;
+
+  constexpr A() : x(0), y(0) {}
+  bool operator==(const A& rhs) const noexcept = default;
+};
+
+void f1() {
+  constexpr A a, b;
+  constexpr bool c = (a == b); // no diagnostic, we should not be comparing the
+                               // unnamed bit-field which is indeterminate
+}
+
+void f2() {
+    A a, b;
+    bool c = (a == b); // no diagnostic nor crash during codegen attempting to
+                       // access info for unnamed bit-field
+}
+}

clang/test/CodeGenCXX/defaulted_equality_ignore_unnamed_bitfields.cpp

+// RUN: %clang_cc1 -std=c++20 %s -triple x86_64-linux -emit-llvm -o - | FileCheck %s
+
+// GH61417
+// Check that we don't attempt to compare the unnamed bitfields
+struct A {
+  unsigned x : 1;
+  unsigned   : 1;
+
+  friend bool operator==(A, A);
+};
+
+
+struct B {
+  unsigned x : 1;
+  unsigned   : 31;
+
+  friend bool operator==(B, B);
+};
+
+bool operator==(A, A) = default;
+// CHECK: define{{.*}} @_Zeq1AS_
+// CHECK: %[[LHS:.+]] = alloca %struct.A, align 4
+// CHECK: %[[RHS:.+]] = alloca %struct.A, align 4
+// CHECK: %[[LHS_LOAD:.+]] = load i8, ptr %[[LHS]], align 4
+// CHECK: %[[LHS_CLEAR:.+]] = and i8 %[[LHS_LOAD]], 1
+// CHECK: %[[LHS_CAST:.+]] = zext i8 %[[LHS_CLEAR]] to i32
+
+// CHECK: %[[RHS_LOAD:.+]] = load i8, ptr %[[RHS]]
+// CHECK: %[[RHS_CLEAR:.+]] = and i8 %[[RHS_LOAD]], 1
+// CHECK: %[[RHS_CAST:.+]] = zext i8 %[[RHS_CLEAR]] to i32
+// CHECK: %[[CMP:.*]] = icmp eq i32 %[[LHS_CAST]], %[[RHS_CAST]]
+// CHECK: ret i1 %[[CMP]]
+
+bool operator==(B, B) = default;
+// CHECK: define{{.*}} @_Zeq1BS_
+// CHECK: %[[LHS_B:.+]] = alloca %struct.B, align 4
+// CHECK: %[[RHS_B:.+]] = alloca %struct.B, align 4
+// CHECK: %[[LHS_LOAD_B:.+]] = load i32, ptr %[[LHS_B]], align 4
+// CHECK: %[[LHS_CLEAR_B:.+]] = and i32 %[[LHS_LOAD_B]], 1
+
+// CHECK: %[[RHS_LOAD_B:.+]] = load i32, ptr %[[RHS_B]]
+// CHECK: %[[RHS_CLEAR_B:.+]] = and i32 %[[RHS_LOAD_B]], 1
+// CHECK: %[[CMP_B:.*]] = icmp eq i32 %[[LHS_CLEAR_B]], %[[RHS_CLEAR_B]]
+// CHECK: ret i1 %[[CMP_B]]