[Lex] Use line markers in preprocessed assembly predefines file

GNU line marker directives are not recognised when preprocessing
assembly files, meaning they can't be used in the predefines file
meaning macros defined on the command line are reported as being
built-in.

Change this to permit line markers but only in the predefines file,
so we can correctly report command line macros as coming from the
command line.

Differential Revision: https://reviews.llvm.org/D145397

clang/docs/ReleaseNotes.rst

@@ -159,6 +159,9 @@ Improvements to Clang's diagnostics
   class if that class was first introduced with a forward declaration.
 - Diagnostic notes and fix-its are now generated for ``ifunc``/``alias`` attributes
   which point to functions whose names are mangled.
+- 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>``.
 
 Bug Fixes in This Version
 -------------------------

clang/lib/Frontend/InitPreprocessor.cpp

@@ -1317,11 +1317,10 @@ void clang::InitializePreprocessor(
   llvm::raw_string_ostream Predefines(PredefineBuffer);
   MacroBuilder Builder(Predefines);
 
-  // Emit line markers for various builtin sections of the file.  We don't do
-  // this in asm preprocessor mode, because "# 4" is not a line marker directive
-  // in this mode.
-  if (!PP.getLangOpts().AsmPreprocessor)
-    Builder.append("# 1 \"<built-in>\" 3");
+  // Emit line markers for various builtin sections of the file. The 3 here
+  // marks <built-in> as being a system header, which suppresses warnings when
+  // the same macro is defined multiple times.
+  Builder.append("# 1 \"<built-in>\" 3");
 
   // Install things like __POWERPC__, __GNUC__, etc into the macro table.
   if (InitOpts.UsePredefines) {
@@ -1359,8 +1358,7 @@ void clang::InitializePreprocessor(
 
   // Add on the predefines from the driver.  Wrap in a #line directive to report
   // that they come from the command line.
-  if (!PP.getLangOpts().AsmPreprocessor)
-    Builder.append("# 1 \"<command line>\" 1");
+  Builder.append("# 1 \"<command line>\" 1");
 
   // Process #define's and #undef's in the order they are given.
   for (unsigned i = 0, e = InitOpts.Macros.size(); i != e; ++i) {
@@ -1372,8 +1370,7 @@ void clang::InitializePreprocessor(
   }
 
   // Exit the command line and go back to <built-in> (2 is LC_LEAVE).
-  if (!PP.getLangOpts().AsmPreprocessor)
-    Builder.append("# 1 \"<built-in>\" 2");
+  Builder.append("# 1 \"<built-in>\" 2");
 
   // If -imacros are specified, include them now.  These are processed before
   // any -include directives.

clang/lib/Lex/PPDirectives.cpp

@@ -1185,8 +1185,12 @@ void Preprocessor::HandleDirective(Token &Result) {
                                     CurPPLexer->getConditionalStackDepth() > 0);
     return;
   case tok::numeric_constant:  // # 7  GNU line marker directive.
-    if (getLangOpts().AsmPreprocessor)
-      break;  // # 4 is not a preprocessor directive in .S files.
+    // In a .S file "# 4" may be a comment so don't treat it as a preprocessor
+    // directive. However do permit it in the predefines file, as we use line
+    // markers to mark the builtin macros as being in a system header.
+    if (getLangOpts().AsmPreprocessor &&
+        SourceMgr.getFileID(SavedHash.getLocation()) != getPredefinesFileID())
+      break;
     return HandleDigitDirective(Result);
   default:
     IdentifierInfo *II = Result.getIdentifierInfo();

clang/test/Preprocessor/directives_asm.S

@@ -0,0 +1,25 @@
+// RUN: %clang -c %s -o /dev/null 2>&1 | FileCheck %s
+
+// Check that preprocessor directives are recognised as such, but lines starting
+// with a # that aren't directives are instead treated as comments.
+
+#define MACRO .warning "This is a macro"
+        MACRO
+
+// CHECK: directives_asm.S:7:9: warning: This is a macro
+
+#not a preprocessing directive
+
+// CHECK-NOT: error: invalid preprocessing directive
+
+# 100
+
+        .warning "line number should not change"
+
+// CHECK: directives_asm.S:17:9: warning: line number should not change
+
+#line 100
+
+        .warning "line number should change"
+
+// CHECK: directives_asm.S:101:9: warning: line number should change

clang/test/Preprocessor/macro_redefined.S

@@ -0,0 +1,10 @@
+// RUN: %clang %s -E -DCLI_MACRO=1 2>&1 | FileCheck %s
+
+#define CLI_MACRO
+// CHECK: macro_redefined.S{{.+}}: warning: 'CLI_MACRO' macro redefined
+// CHECK: <command line>{{.+}}: note: previous definition is here
+
+#define REGULAR_MACRO
+#define REGULAR_MACRO 1
+// CHECK: macro_redefined.S{{.+}}: warning: 'REGULAR_MACRO' macro redefined
+// CHECK: macro_redefined.S{{.+}}: note: previous definition is here