[PATCH] Allow _MSC_EXTENSIONS macro on non-Windows targets

[Yunzhong Gao]

  Hi David, Richard,
  The following patch implements a new __has_keyword() test.
  There are several existing keyword tests in clang/test/Lexer directory that
  can be rewritten to make use of this new test. I will do that in a follow-up
  patch if this test looks acceptable,
  - Gao

http://llvm-reviews.chandlerc.com/D3034

CHANGE SINCE LAST DIFF
  http://llvm-reviews.chandlerc.com/D3034?vs=7788&id=7843#toc

Files:
  lib/Lex/PPMacroExpansion.cpp
  test/Lexer/has_keywords.c

Index: lib/Lex/PPMacroExpansion.cpp
===================================================================
--- lib/Lex/PPMacroExpansion.cpp
+++ lib/Lex/PPMacroExpansion.cpp
@@ -102,6 +102,7 @@
   Ident__has_extension    = RegisterBuiltinMacro(*this, "__has_extension");
   Ident__has_builtin      = RegisterBuiltinMacro(*this, "__has_builtin");
   Ident__has_attribute    = RegisterBuiltinMacro(*this, "__has_attribute");
+  Ident__has_keyword      = RegisterBuiltinMacro(*this, "__has_keyword");
   Ident__has_include      = RegisterBuiltinMacro(*this, "__has_include");
   Ident__has_include_next = RegisterBuiltinMacro(*this, "__has_include_next");
   Ident__has_warning      = RegisterBuiltinMacro(*this, "__has_warning");
@@ -1057,6 +1058,16 @@
         .Default(false);
 }
 
+/// HasKeyword -  Return true if we recognize the specified keyword
+static bool HasKeyword(tok::TokenKind Kind) {
+  switch (Kind) {
+#define KEYWORD(X,Y) case tok::kw_ ## X: return true;
+#include "clang/Basic/TokenKinds.def"
+   default: break;
+  }
+  return false;
+}
+
 /// EvaluateHasIncludeCommon - Process a '__has_include("path")'
 /// or '__has_include_next("path")' expression.
 /// Returns true if successful.
@@ -1367,6 +1378,7 @@
     Tok.setKind(tok::numeric_constant);
   } else if (II == Ident__has_feature   ||
              II == Ident__has_extension ||
+             II == Ident__has_keyword   ||
              II == Ident__has_builtin   ||
              II == Ident__has_attribute) {
     // The argument to these builtins should be a parenthesized identifier.
@@ -1391,6 +1403,8 @@
     bool Value = false;
     if (!IsValid)
       Diag(StartLoc, diag::err_feature_check_malformed);
+    else if (II == Ident__has_keyword)
+      Value = HasKeyword(FeatureII->getTokenID());
     else if (II == Ident__has_builtin) {
       // Check for a builtin is trivial.
       Value = FeatureII->getBuiltinID() != 0;
Index: test/Lexer/has_keywords.c
===================================================================
--- test/Lexer/has_keywords.c
+++ test/Lexer/has_keywords.c
@@ -0,0 +1,29 @@
+// RUN: %clang_cc1 -std=c99 -E %s -o - | FileCheck --check-prefix=CHECK-NONE %s
+
+// RUN: %clang_cc1 -std=gnu89 -E %s -o - \
+// RUN:     | FileCheck --check-prefix=CHECK-GNU-KEYWORDS %s
+// RUN: %clang_cc1 -std=c99 -fgnu-keywords -E %s -o - \
+// RUN:     | FileCheck --check-prefix=CHECK-GNU-KEYWORDS %s
+// RUN: %clang_cc1 -std=gnu89 -fno-gnu-keywords -E %s -o - \
+// RUN:     | FileCheck --check-prefix=CHECK-NONE %s
+
+// RUN: %clang_cc1 -std=c99 -fms-extensions -E %s -o - \
+// RUN:     | FileCheck --check-prefix=CHECK-MS-KEYWORDS %s
+
+void f() {
+// CHECK-NONE: int asm
+// CHECK-GNU-KEYWORDS: asm ("ret" : :)
+#if __has_keyword(asm)
+  asm ("ret" : :);
+#else
+  int asm;
+#endif
+}
+
+// CHECK-NONE: no_ms_wchar
+// CHECK-MS-KEYWORDS: has_ms_wchar
+#if __has_keyword(__wchar_t)
+void has_ms_wchar();
+#else
+void no_ms_wchar();
+#endif
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