[PATCH] D145793: [clang][AST] Improve diagnostic for `nullptr` constexpr function pointer call

[Aaron Ballman via Phabricator via cfe-commits]

This revision was landed with ongoing or failed builds.
This revision was automatically updated to reflect the committed changes.
Closed by commit rG6b48d202ef49: [clang][AST] Improve diagnostic for `nullptr` constexpr function pointer call (authored by hazohelet, committed by aaron.ballman).

Changed prior to commit:
  https://reviews.llvm.org/D145793?vs=504678&id=504722#toc

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D145793/new/

https://reviews.llvm.org/D145793

Files:
  clang/docs/ReleaseNotes.rst
  clang/include/clang/Basic/DiagnosticASTKinds.td
  clang/lib/AST/ExprConstant.cpp
  clang/test/SemaCXX/constant-expression-cxx11.cpp


Index: clang/test/SemaCXX/constant-expression-cxx11.cpp
===================================================================
--- clang/test/SemaCXX/constant-expression-cxx11.cpp
+++ clang/test/SemaCXX/constant-expression-cxx11.cpp
@@ -279,7 +279,7 @@
   constexpr auto Select(int n) -> int (*)(int) {
     return n == 2 ? &Double : n == 3 ? &Triple : n == 4 ? &Quadruple : 0;
   }
-  constexpr int Apply(int (*F)(int), int n) { return F(n); } // expected-note {{subexpression}}
+  constexpr int Apply(int (*F)(int), int n) { return F(n); } // expected-note {{'F' evaluates to a null function pointer}}
 
   static_assert(1 + Apply(Select(4), 5) + Apply(Select(3), 7) == 42, "");
 
Index: clang/lib/AST/ExprConstant.cpp
===================================================================
--- clang/lib/AST/ExprConstant.cpp
+++ clang/lib/AST/ExprConstant.cpp
@@ -7668,6 +7668,11 @@
 
       if (!CalleeLV.getLValueOffset().isZero())
         return Error(Callee);
+      if (CalleeLV.isNullPointer()) {
+        Info.FFDiag(Callee, diag::note_constexpr_null_callee)
+            << const_cast<Expr *>(Callee);
+        return false;
+      }
       FD = dyn_cast_or_null<FunctionDecl>(
           CalleeLV.getLValueBase().dyn_cast<const ValueDecl *>());
       if (!FD)
Index: clang/include/clang/Basic/DiagnosticASTKinds.td
===================================================================
--- clang/include/clang/Basic/DiagnosticASTKinds.td
+++ clang/include/clang/Basic/DiagnosticASTKinds.td
@@ -127,6 +127,8 @@
   "access array element of|perform pointer arithmetic on|"
   "access real component of|"
   "access imaginary component of}0 null pointer">;
+def note_constexpr_null_callee : Note<
+  "'%0' evaluates to a null function pointer">;
 def note_constexpr_function_param_value_unknown : Note<
   "function parameter %0 with unknown value cannot be used in a constant "
   "expression">;
Index: clang/docs/ReleaseNotes.rst
===================================================================
--- clang/docs/ReleaseNotes.rst
+++ clang/docs/ReleaseNotes.rst
@@ -165,6 +165,8 @@
 - Diagnostics relating to macros on the command line of a preprocessed assembly
   file are now reported as coming from the file ``<command line>`` instead of
   ``<built-in>``.
+- Clang constexpr evaluator now provides a more concise diagnostic when calling
+  function pointer that is known to be null.
 
 Bug Fixes in This Version
 -------------------------


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