[PATCH] D131532: [Sema] Only invoke DiagnoseNullConversions for CPlusPlus (-Wnull-conversion)

[Justin Stitt via Phabricator via cfe-commits]

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-Wnull-conversion is not supported in C and therefore
DiagnoseNullConversions should only be called for C++.

When testing this change on Linux Kernel builds (x86_64 defconfig) we
see an approximate 2.1% reduction in build times! This is mainly caused
by two methods no longer needing to be invoked as often:

1. ExprConstant::CheckICE and 2) IntExprEvaluator::VisitBinaryOperator.

The former has had its total cpu cycles reduced by ~90% and the latter
by about ~50% for Kernel builds.

The C++ Standard (https://isocpp.org/files/papers/N4860.pdf) states
that "NULL is an implementation-defined null pointer constant" and
"possible definitions include 0, 0L, but not (void*)0". Which may
explain the difference in C and C++ as seen here: https://godbolt.org/z/c5j8fY39


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D131532

Files:
  clang/lib/Sema/SemaChecking.cpp


Index: clang/lib/Sema/SemaChecking.cpp
===================================================================
--- clang/lib/Sema/SemaChecking.cpp
+++ clang/lib/Sema/SemaChecking.cpp
@@ -13865,7 +13865,8 @@
     }
   }
 
-  DiagnoseNullConversion(S, E, T, CC);
+  if (S.getLangOpts().CPlusPlus)
+    DiagnoseNullConversion(S, E, T, CC);
 
   S.DiscardMisalignedMemberAddress(Target, E);
 


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