[clang] Warning for incorrect useof 'pure' attribute (PR #78200)

[via cfe-commits]

https://github.com/kelbon updated https://github.com/llvm/llvm-project/pull/78200

>From e8c799b54c3e0b8088dbc19aaac0ef066baf136e Mon Sep 17 00:00:00 2001
From: Kelbon Nik <kelbonage at gmail.com>
Date: Mon, 15 Jan 2024 22:24:34 +0400
Subject: [PATCH 1/3] add warning and test

---
 clang/include/clang/Basic/DiagnosticGroups.td    | 1 +
 clang/include/clang/Basic/DiagnosticSemaKinds.td | 7 +++++++
 clang/lib/Sema/SemaDecl.cpp                      | 7 +++++++
 clang/test/Sema/incorrect_pure.cpp               | 7 +++++++
 4 files changed, 22 insertions(+)
 create mode 100644 clang/test/Sema/incorrect_pure.cpp

diff --git a/clang/include/clang/Basic/DiagnosticGroups.td b/clang/include/clang/Basic/DiagnosticGroups.td
index 6765721ae7002c..9fcf2be2e45458 100644
--- a/clang/include/clang/Basic/DiagnosticGroups.td
+++ b/clang/include/clang/Basic/DiagnosticGroups.td
@@ -414,6 +414,7 @@ def : DiagGroup<"c++2a-compat", [CXX20Compat]>;
 def : DiagGroup<"c++2a-compat-pedantic", [CXX20CompatPedantic]>;
 
 def ExitTimeDestructors : DiagGroup<"exit-time-destructors">;
+def IncorrectAttributeUsage : DiagGroup<"incorrect-attribute-usage">;
 def FlexibleArrayExtensions : DiagGroup<"flexible-array-extensions">;
 def FourByteMultiChar : DiagGroup<"four-char-constants">;
 def GlobalConstructors : DiagGroup<"global-constructors"> {
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 03b0122d1c08f7..1df075119a482f 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -692,6 +692,13 @@ def warn_maybe_falloff_nonvoid_function : Warning<
 def warn_falloff_nonvoid_function : Warning<
   "non-void function does not return a value">,
   InGroup<ReturnType>;
+def warn_pure_attr_on_cxx_constructor : Warning<
+  "constructor cannot be 'pure' (undefined behavior)">,
+  InGroup<IncorrectAttributeUsage>;
+def warn_pure_function_returns_void : Warning<
+  "'pure' attribute on function returning 'void'">,
+  InGroup<IncorrectAttributeUsage>;
+
 def err_maybe_falloff_nonvoid_block : Error<
   "non-void block does not return a value in all control paths">;
 def err_falloff_nonvoid_block : Error<
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index dae98f3a7406e8..86dc022fbe055d 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -11899,6 +11899,13 @@ bool Sema::CheckFunctionDeclaration(Scope *S, FunctionDecl *NewFD,
     NewFD->setInvalidDecl();
   }
 
+  if (NewFD->hasAttr<PureAttr>() || NewFD->hasAttr<ConstAttr>()) {
+    if (isa<CXXConstructorDecl>(NewFD))
+      Diag(NewFD->getLocation(), diag::warn_pure_attr_on_cxx_constructor);
+    else if (NewFD->getReturnType()->isVoidType())
+      Diag(NewFD->getLocation(), diag::warn_pure_function_returns_void);
+  }
+
   // C++11 [dcl.constexpr]p8:
   //   A constexpr specifier for a non-static member function that is not
   //   a constructor declares that member function to be const.
diff --git a/clang/test/Sema/incorrect_pure.cpp b/clang/test/Sema/incorrect_pure.cpp
new file mode 100644
index 00000000000000..ce02309f086386
--- /dev/null
+++ b/clang/test/Sema/incorrect_pure.cpp
@@ -0,0 +1,7 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+
+[[gnu::pure]] void foo(); // expected-warning{{'pure' attribute on function returning 'void'}}
+
+struct A {
+    [[gnu::pure]] A(); // expected-warning{{constructor cannot be 'pure' (undefined behavior)}}
+};

>From d152fa4881d6052bfad33c922f276d4909c305ec Mon Sep 17 00:00:00 2001
From: Kelbon Nik <kelbonage at gmail.com>
Date: Tue, 16 Jan 2024 00:03:47 +0400
Subject: [PATCH 2/3] fix old incorrect test

---
 clang/test/Analysis/call-invalidation.cpp           | 8 ++++----
 clang/test/CodeGen/pragma-weak.c                    | 6 +++---
 clang/test/Interpreter/disambiguate-decl-stmt.cpp   | 4 ++--
 clang/test/SemaCXX/cxx0x-cursory-default-delete.cpp | 2 +-
 clang/test/SemaCXX/warn-unused-value-cxx11.cpp      | 2 +-
 5 files changed, 11 insertions(+), 11 deletions(-)

diff --git a/clang/test/Analysis/call-invalidation.cpp b/clang/test/Analysis/call-invalidation.cpp
index ef6505e19cf803..727217f228b054 100644
--- a/clang/test/Analysis/call-invalidation.cpp
+++ b/clang/test/Analysis/call-invalidation.cpp
@@ -90,8 +90,8 @@ void testConstReferenceStruct() {
 }
 
 
-void usePointerPure(int * const *) __attribute__((pure));
-void usePointerConst(int * const *) __attribute__((const));
+int usePointerPure(int * const *) __attribute__((pure));
+int usePointerConst(int * const *) __attribute__((const));
 
 void testPureConst() {
   extern int global;
@@ -104,11 +104,11 @@ void testPureConst() {
   clang_analyzer_eval(x == 42); // expected-warning{{TRUE}}
   clang_analyzer_eval(global == -5); // expected-warning{{TRUE}}
 
-  usePointerPure(&p);
+  (void)usePointerPure(&p);
   clang_analyzer_eval(x == 42); // expected-warning{{TRUE}}
   clang_analyzer_eval(global == -5); // expected-warning{{TRUE}}
 
-  usePointerConst(&p);
+  (void)usePointerConst(&p);
   clang_analyzer_eval(x == 42); // expected-warning{{TRUE}}
   clang_analyzer_eval(global == -5); // expected-warning{{TRUE}}
 
diff --git a/clang/test/CodeGen/pragma-weak.c b/clang/test/CodeGen/pragma-weak.c
index 52328bf9ff1be7..d4011628bda7f1 100644
--- a/clang/test/CodeGen/pragma-weak.c
+++ b/clang/test/CodeGen/pragma-weak.c
@@ -16,7 +16,7 @@
 // CHECK-DAG: @declfirstattr = weak{{.*}} alias void (), ptr @__declfirstattr
 // CHECK-DAG: @mix2 = weak{{.*}} alias void (), ptr @__mix2
 // CHECK-DAG: @a1 = weak{{.*}} alias void (), ptr @__a1
-// CHECK-DAG: @xxx = weak{{.*}} alias void (), ptr @__xxx
+// CHECK-DAG: @xxx = weak{{.*}} alias int (), ptr @__xxx
 // CHECK-DAG: @undecfunc_alias1 = weak{{.*}} alias void (), ptr @undecfunc
 // CHECK-DAG: @undecfunc_alias2 = weak{{.*}} alias void (), ptr @undecfunc
 // CHECK-DAG: @undecfunc_alias3 = weak{{.*}} alias void (), ptr @undecfunc
@@ -137,8 +137,8 @@ void __a1(void) {}
 // CHECK: define{{.*}} void @__a1() [[NI:#[0-9]+]]
 
 #pragma weak xxx = __xxx
-__attribute((pure,noinline,const)) void __xxx(void) { }
-// CHECK: void @__xxx() [[RN:#[0-9]+]]
+__attribute((pure,noinline,const)) int __xxx(void) { return 0; }
+// CHECK: int @__xxx() [[RN:#[0-9]+]]
 
 ///////////// PR28611: Try multiple aliases of same undeclared symbol or alias
 #pragma weak undecfunc_alias1 = undecfunc
diff --git a/clang/test/Interpreter/disambiguate-decl-stmt.cpp b/clang/test/Interpreter/disambiguate-decl-stmt.cpp
index a49d7013c540ac..1f4d5e267288bc 100644
--- a/clang/test/Interpreter/disambiguate-decl-stmt.cpp
+++ b/clang/test/Interpreter/disambiguate-decl-stmt.cpp
@@ -95,10 +95,10 @@ Ns::Ns::Fs();
 Ns::Ns::Ns();
 
 struct Attrs1 { Attrs1(); };
-Attrs1::Attrs1() __attribute((pure)) = default;
+Attrs1::Attrs1() __attribute((noreturn)) = default;
 
 struct Attrs2 { Attrs2(); };
-__attribute((pure)) Attrs2::Attrs2() = default;
+__attribute((noreturn)) Attrs2::Attrs2() = default;
 
 // Extra semicolon
 namespace N {};
diff --git a/clang/test/SemaCXX/cxx0x-cursory-default-delete.cpp b/clang/test/SemaCXX/cxx0x-cursory-default-delete.cpp
index 9d68a0e5d358f6..6ae146f0d08c7d 100644
--- a/clang/test/SemaCXX/cxx0x-cursory-default-delete.cpp
+++ b/clang/test/SemaCXX/cxx0x-cursory-default-delete.cpp
@@ -194,7 +194,7 @@ struct except_spec_d_match : except_spec_a, except_spec_b {
 // gcc-compatibility: allow attributes on default definitions
 // (but not normal definitions)
 struct S { S(); };
-S::S() __attribute((pure)) = default;
+S::S() __attribute((noreturn)) = default;
 
 using size_t = decltype(sizeof(0));
 void *operator new(size_t) = delete; // expected-error {{deleted definition must be first declaration}} expected-note {{implicit}}
diff --git a/clang/test/SemaCXX/warn-unused-value-cxx11.cpp b/clang/test/SemaCXX/warn-unused-value-cxx11.cpp
index a6f41c3fd6b3b2..687278a98f4e1a 100644
--- a/clang/test/SemaCXX/warn-unused-value-cxx11.cpp
+++ b/clang/test/SemaCXX/warn-unused-value-cxx11.cpp
@@ -1,6 +1,6 @@
 // RUN: %clang_cc1 -std=c++11 -fsyntax-only -verify -Wunused-value %s
 
-void f() __attribute__((const));
+int f() __attribute__((const));
 
 namespace PR18571 {
 // Unevaluated contexts should not trigger unused result warnings.

>From 58e264511cd8b2f2eb20bb23ec797d8dadd5ac19 Mon Sep 17 00:00:00 2001
From: Kelbon Nik <kelbonage at gmail.com>
Date: Wed, 17 Jan 2024 15:00:39 +0400
Subject: [PATCH 3/3] release notes, update warning message, handle pure &&
 const declarations

---
 clang/docs/ReleaseNotes.rst                   |  2 +-
 clang/include/clang/Basic/DiagnosticGroups.td |  1 -
 .../clang/Basic/DiagnosticSemaKinds.td        | 10 +++----
 clang/lib/Sema/SemaDecl.cpp                   | 27 ++++++++++++++-----
 clang/test/CodeGen/pragma-weak.c              |  6 ++---
 clang/test/Sema/attr-print.c                  |  8 +++---
 clang/test/Sema/incorrect_pure.cpp            | 11 ++++++--
 7 files changed, 43 insertions(+), 22 deletions(-)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index d63781cf8b11bf..e929852b0994a1 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -569,7 +569,7 @@ Improvements to Clang's diagnostics
   and template friend declarations with a constraint that depends on a template parameter from an
   enclosing template must be a definition.
 - Clang now diagnoses function/variable templates that shadow their own template parameters, e.g. ``template<class T> void T();``.
-
+- Clang now diagnoses incorrect usage of ``const`` and ``pure`` attributes, so ``-Wignored-attributes`` diagnoses more cases.
 
 Improvements to Clang's time-trace
 ----------------------------------
diff --git a/clang/include/clang/Basic/DiagnosticGroups.td b/clang/include/clang/Basic/DiagnosticGroups.td
index 9fcf2be2e45458..6765721ae7002c 100644
--- a/clang/include/clang/Basic/DiagnosticGroups.td
+++ b/clang/include/clang/Basic/DiagnosticGroups.td
@@ -414,7 +414,6 @@ def : DiagGroup<"c++2a-compat", [CXX20Compat]>;
 def : DiagGroup<"c++2a-compat-pedantic", [CXX20CompatPedantic]>;
 
 def ExitTimeDestructors : DiagGroup<"exit-time-destructors">;
-def IncorrectAttributeUsage : DiagGroup<"incorrect-attribute-usage">;
 def FlexibleArrayExtensions : DiagGroup<"flexible-array-extensions">;
 def FourByteMultiChar : DiagGroup<"four-char-constants">;
 def GlobalConstructors : DiagGroup<"global-constructors"> {
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 1df075119a482f..ee74a8211c34af 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -692,12 +692,12 @@ def warn_maybe_falloff_nonvoid_function : Warning<
 def warn_falloff_nonvoid_function : Warning<
   "non-void function does not return a value">,
   InGroup<ReturnType>;
-def warn_pure_attr_on_cxx_constructor : Warning<
-  "constructor cannot be 'pure' (undefined behavior)">,
-  InGroup<IncorrectAttributeUsage>;
+def warn_const_attr_with_pure_attr : Warning<
+  "'const' attribute imposes more restrictions, 'pure' attribute ignored">,
+  InGroup<IgnoredAttributes>;
 def warn_pure_function_returns_void : Warning<
-  "'pure' attribute on function returning 'void'">,
-  InGroup<IncorrectAttributeUsage>;
+  "'%select{pure|const}0' attribute on function returning 'void', attribute ignored">,
+  InGroup<IgnoredAttributes>;
 
 def err_maybe_falloff_nonvoid_block : Error<
   "non-void block does not return a value in all control paths">;
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 86dc022fbe055d..5b35783a268948 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -11802,6 +11802,26 @@ static bool CheckMultiVersionFunction(Sema &S, FunctionDecl *NewFD,
                                          OldDecl, Previous);
 }
 
+static void CheckFunctionDeclarationAttributesUsage(Sema &S,
+                                                    FunctionDecl *NewFD) {
+  bool IsPure = NewFD->hasAttr<PureAttr>();
+  bool IsConst = NewFD->hasAttr<ConstAttr>();
+
+  if (IsPure && IsConst) {
+    S.Diag(NewFD->getLocation(), diag::warn_const_attr_with_pure_attr);
+    NewFD->dropAttr<PureAttr>();
+  }
+  if (IsPure || IsConst) {
+    // Constructors and destructors are functions which return void, so are handled here as well.
+    if (NewFD->getReturnType()->isVoidType()) {
+      S.Diag(NewFD->getLocation(), diag::warn_pure_function_returns_void)
+          << IsConst;
+      NewFD->dropAttr<PureAttr>();
+      NewFD->dropAttr<ConstAttr>();
+    }
+  }
+}
+
 /// Perform semantic checking of a new function declaration.
 ///
 /// Performs semantic analysis of the new function declaration
@@ -11899,12 +11919,7 @@ bool Sema::CheckFunctionDeclaration(Scope *S, FunctionDecl *NewFD,
     NewFD->setInvalidDecl();
   }
 
-  if (NewFD->hasAttr<PureAttr>() || NewFD->hasAttr<ConstAttr>()) {
-    if (isa<CXXConstructorDecl>(NewFD))
-      Diag(NewFD->getLocation(), diag::warn_pure_attr_on_cxx_constructor);
-    else if (NewFD->getReturnType()->isVoidType())
-      Diag(NewFD->getLocation(), diag::warn_pure_function_returns_void);
-  }
+  CheckFunctionDeclarationAttributesUsage(*this, NewFD);
 
   // C++11 [dcl.constexpr]p8:
   //   A constexpr specifier for a non-static member function that is not
diff --git a/clang/test/CodeGen/pragma-weak.c b/clang/test/CodeGen/pragma-weak.c
index d4011628bda7f1..ea508a485ef612 100644
--- a/clang/test/CodeGen/pragma-weak.c
+++ b/clang/test/CodeGen/pragma-weak.c
@@ -16,7 +16,7 @@
 // CHECK-DAG: @declfirstattr = weak{{.*}} alias void (), ptr @__declfirstattr
 // CHECK-DAG: @mix2 = weak{{.*}} alias void (), ptr @__mix2
 // CHECK-DAG: @a1 = weak{{.*}} alias void (), ptr @__a1
-// CHECK-DAG: @xxx = weak{{.*}} alias int (), ptr @__xxx
+// CHECK-DAG: @xxx = weak{{.*}} alias i32 (), ptr @__xxx
 // CHECK-DAG: @undecfunc_alias1 = weak{{.*}} alias void (), ptr @undecfunc
 // CHECK-DAG: @undecfunc_alias2 = weak{{.*}} alias void (), ptr @undecfunc
 // CHECK-DAG: @undecfunc_alias3 = weak{{.*}} alias void (), ptr @undecfunc
@@ -137,8 +137,8 @@ void __a1(void) {}
 // CHECK: define{{.*}} void @__a1() [[NI:#[0-9]+]]
 
 #pragma weak xxx = __xxx
-__attribute((pure,noinline,const)) int __xxx(void) { return 0; }
-// CHECK: int @__xxx() [[RN:#[0-9]+]]
+__attribute((noinline,const)) int __xxx(void) { return 0; }
+// CHECK: i32 @__xxx() [[RN:#[0-9]+]]
 
 ///////////// PR28611: Try multiple aliases of same undeclared symbol or alias
 #pragma weak undecfunc_alias1 = undecfunc
diff --git a/clang/test/Sema/attr-print.c b/clang/test/Sema/attr-print.c
index ffa27de4a5d306..8492356e5d2e57 100644
--- a/clang/test/Sema/attr-print.c
+++ b/clang/test/Sema/attr-print.c
@@ -9,11 +9,11 @@ __declspec(align(4)) int y;
 // CHECK: short arr[3] __attribute__((aligned));
 short arr[3] __attribute__((aligned));
 
-// CHECK: void foo(void) __attribute__((const));
-void foo(void) __attribute__((const));
+// CHECK: int foo(void) __attribute__((const));
+int foo(void) __attribute__((const));
 
-// CHECK: void bar(void) __attribute__((__const));
-void bar(void) __attribute__((__const));
+// CHECK: int bar(void) __attribute__((__const));
+int bar(void) __attribute__((__const));
 
 // CHECK: int * __ptr32 p32;
 int * __ptr32 p32;
diff --git a/clang/test/Sema/incorrect_pure.cpp b/clang/test/Sema/incorrect_pure.cpp
index ce02309f086386..1fa17785ec3880 100644
--- a/clang/test/Sema/incorrect_pure.cpp
+++ b/clang/test/Sema/incorrect_pure.cpp
@@ -1,7 +1,14 @@
 // RUN: %clang_cc1 -fsyntax-only -verify %s
 
-[[gnu::pure]] void foo(); // expected-warning{{'pure' attribute on function returning 'void'}}
+[[gnu::pure]] void foo(); // expected-warning{{'pure' attribute on function returning 'void', attribute ignored}}
+
+[[gnu::const]] void bar(); // expected-warning{{'const' attribute on function returning 'void', attribute ignored}}
 
 struct A {
-    [[gnu::pure]] A(); // expected-warning{{constructor cannot be 'pure' (undefined behavior)}}
+    [[gnu::pure]] A(); // expected-warning{{'pure' attribute on function returning 'void', attribute ignored}}
+
+    [[gnu::const]] A(int); // expected-warning{{'const' attribute on function returning 'void', attribute ignored}}
+    [[gnu::pure]] ~A(); // expected-warning{{'pure' attribute on function returning 'void', attribute ignored}}
+
+    [[gnu::const]] [[gnu::pure]] int m(); // expected-warning{{'const' attribute imposes more restrictions, 'pure' attribute ignored}}
 };