[PATCH] D141310: [clang] add -Wcompare-function-pointers

[Adrian Dole via Phabricator via cfe-commits]

adriandole updated this revision to Diff 490671.
adriandole added a comment.

Only trigger this warning when comparing function pointers of the same type, since comparing distinct types is already an error.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D141310/new/

https://reviews.llvm.org/D141310

Files:
  clang/docs/ReleaseNotes.rst
  clang/include/clang/Basic/DiagnosticGroups.td
  clang/include/clang/Basic/DiagnosticSemaKinds.td
  clang/lib/Sema/SemaExpr.cpp
  clang/test/SemaCXX/compare-function-pointer.cpp


Index: clang/test/SemaCXX/compare-function-pointer.cpp
===================================================================
--- clang/test/SemaCXX/compare-function-pointer.cpp
+++ clang/test/SemaCXX/compare-function-pointer.cpp
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -fsyntax-only -std=c++20 -verify %s
+// RUN: %clang_cc1 -fsyntax-only -std=c++20 -verify -Wcompare-function-pointers %s
 
 using fp0_t = void (*)();
 using fp1_t = int (*)();
@@ -6,8 +6,8 @@
 extern fp0_t a, b;
 extern fp1_t c;
 
-bool eq0 = a == b;
-bool ne0 = a != b;
+bool eq0 = a == b;  // expected-warning {{distinct function pointers ('fp0_t' (aka 'void (*)()') and 'fp0_t')}}
+bool ne0 = a != b;  // expected-warning {{distinct function pointers}}
 bool lt0 = a < b;   // expected-warning {{ordered comparison of function pointers ('fp0_t' (aka 'void (*)()') and 'fp0_t')}}
 bool le0 = a <= b;  // expected-warning {{ordered comparison of function pointers}}
 bool gt0 = a > b;   // expected-warning {{ordered comparison of function pointers}}
Index: clang/lib/Sema/SemaExpr.cpp
===================================================================
--- clang/lib/Sema/SemaExpr.cpp
+++ clang/lib/Sema/SemaExpr.cpp
@@ -12714,6 +12714,13 @@
                                    LHS.get()->getSourceRange());
   }
 
+  if (!IsOrdered && LHSType->isFunctionPointerType() &&
+      RHSType->isFunctionPointerType() && !LHSIsNull && !RHSIsNull &&
+      RHSType == LHSType)
+    Diag(Loc, diag::warn_typecheck_comparison_of_function_pointers)
+          << LHSType << RHSType
+          << LHS.get()->getSourceRange() << RHS.get()->getSourceRange();
+
   if (IsOrdered && LHSType->isFunctionPointerType() &&
       RHSType->isFunctionPointerType()) {
     // Valid unless a relational comparison of function pointers
Index: clang/include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -7010,6 +7010,10 @@
   "%0 is %select{|in}2complete and "
   "%1 is %select{|in}3complete">,
   InGroup<C11>;
+def warn_typecheck_comparison_of_function_pointers : Warning<
+  "distinct function pointers (%0 and %1) may compare equal "
+  "when using identical code folding">,
+  InGroup<CompareFunctionPointers>, DefaultIgnore;
 def warn_typecheck_ordered_comparison_of_function_pointers : Warning<
   "ordered comparison of function pointers (%0 and %1)">,
   InGroup<OrderedCompareFunctionPointers>;
Index: clang/include/clang/Basic/DiagnosticGroups.td
===================================================================
--- clang/include/clang/Basic/DiagnosticGroups.td
+++ clang/include/clang/Basic/DiagnosticGroups.td
@@ -565,6 +565,7 @@
 def DeprecatedObjCIsaUsage : DiagGroup<"deprecated-objc-isa-usage">;
 def ExplicitInitializeCall : DiagGroup<"explicit-initialize-call">;
 def OrderedCompareFunctionPointers : DiagGroup<"ordered-compare-function-pointers">;
+def CompareFunctionPointers : DiagGroup<"compare-function-pointers", [OrderedCompareFunctionPointers]>;
 def PackedNonPod : DiagGroup<"packed-non-pod">;
 def Packed : DiagGroup<"packed", [PackedNonPod]>;
 def Padded : DiagGroup<"padded">;
Index: clang/docs/ReleaseNotes.rst
===================================================================
--- clang/docs/ReleaseNotes.rst
+++ clang/docs/ReleaseNotes.rst
@@ -465,6 +465,8 @@
 - Clang now automatically adds ``[[clang::lifetimebound]]`` to the parameters of
   ``std::move, std::forward`` et al, this enables Clang to diagnose more cases
   where the returned reference outlives the object.
+- Add ``-Wcompare-function-pointers`` to warn about comparisons that may have their behavior
+  change when enabling the identical code folding optimization feature of some linkers.
 
 Non-comprehensive list of changes in this release
 -------------------------------------------------


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