make sure to not warn about unused macros from -D

llunak · llunak · commit 5c8c9905c249 · 2020-04-27T21:26:13.000+02:00
If a PCH is used for compilation, SourceManager::isInMainFile() returns true even for the "<built-in>" predefines area. Using -D only for the TU compilation may trigger -Wunused-macros for it. It is admitedly a bit fishy to set a macro only for a TU and not for the PCH, but this works fine if the PCH does not use the macro (I couldn't find a statement on this for Clang, but GCC explicitly allows this in the docs). Differential Revision: https://reviews.llvm.org/D73846
diff --git a/clang/lib/Lex/PPDirectives.cpp b/clang/lib/Lex/PPDirectives.cpp
@@ -2802,7 +2802,9 @@ void Preprocessor::HandleDefineDirective(
   // warn-because-unused-macro set. If it gets used it will be removed from set.
   if (getSourceManager().isInMainFile(MI->getDefinitionLoc()) &&
       !Diags->isIgnored(diag::pp_macro_not_used, MI->getDefinitionLoc()) &&
-      !MacroExpansionInDirectivesOverride) {
+      !MacroExpansionInDirectivesOverride &&
+      getSourceManager().getFileID(MI->getDefinitionLoc()) !=
+          getPredefinesFileID()) {
     MI->setIsWarnIfUnused(true);
     WarnUnusedMacroLocs.insert(MI->getDefinitionLoc());
   }
diff --git a/clang/test/PCH/cli-macro.c b/clang/test/PCH/cli-macro.c
@@ -0,0 +1,12 @@
+// Test this without pch.
+// RUN: %clang_cc1 -Wunused-macros -Dunused=1 -fsyntax-only -verify %s
+
+// Test with pch.
+// RUN: %clang_cc1 -Wunused-macros -emit-pch -o %t %s
+// RUN: %clang_cc1 -Wunused-macros -Dunused=1 -include-pch %t -fsyntax-only -verify %s
+
+// expected-no-diagnostics
+
+// -Dunused=1 is intentionally not set for the pch.
+// There still should be no unused warning for a macro from the command line.
+
