Add -std=c17 as a flag

[aaron.ballman]

Summary

GCC currently supports the flags -std=c17, -std=gnu17, and -std=iso9899:2017, with the only functional difference with C11 being the value of STDC_VERSION. These flags are documented at: https://gcc.gnu.org/onlinedocs/gcc/Standards.html

This patch adds these flags and updates STDC_VERSION based on the C17 FDIS. Note that C17 is going out for balloting in December. I spoke with the GCC maintainer for the flags about what they will do when C17 is published in 2018 and their plan is to add c18, iso9899:2018, and gnu18. I will add the additional flags to Clang when the C17 ballot succeeds.

[aaron.ballman]

Ping

[aaron.ballman]

Ping

[aaron.ballman]

Rebased on ToT and given more context.

[aaron.ballman]

In D40225#944113, @aaron.ballman wrote:

Rebased on ToT and given more context.

Ping. I'd like to get this in before the 6.0 branch.

[rsmith]

LGTM, makes sense to add this for GCC compatibility even if the standard ends up being called C18.

[aaron.ballman]

Commit in r320089.

include/clang/Basic/LangOptions.def

 #ifndef BENIGN_VALUE_LANGOPT
 #  define BENIGN_VALUE_LANGOPT(Name, Bits, Default, Description) \
      COMPATIBLE_VALUE_LANGOPT(Name, Bits, Default, Description)
 #endif
 
 // FIXME: A lot of the BENIGN_ options should be COMPATIBLE_ instead.
 LANGOPT(C99               , 1, 0, "C99")
 LANGOPT(C11               , 1, 0, "C11")
+LANGOPT(C17               , 1, 0, "C17")
 LANGOPT(MSVCCompat        , 1, 0, "Microsoft Visual C++ full compatibility mode")
 LANGOPT(MicrosoftExt      , 1, 0, "Microsoft C++ extensions")
 LANGOPT(AsmBlocks         , 1, 0, "Microsoft inline asm blocks")
 LANGOPT(Borland           , 1, 0, "Borland extensions")
 LANGOPT(CPlusPlus         , 1, 0, "C++")
 LANGOPT(CPlusPlus11       , 1, 0, "C++11")
 LANGOPT(CPlusPlus14       , 1, 0, "C++14")
 LANGOPT(CPlusPlus17       , 1, 0, "C++17")

include/clang/Frontend/LangStandard.h

 namespace clang {
 
 namespace frontend {
 
 enum LangFeatures {
   LineComment = (1 << 0),
   C99 = (1 << 1),
   C11 = (1 << 2),
-  CPlusPlus = (1 << 3),
-  CPlusPlus11 = (1 << 4),
-  CPlusPlus14 = (1 << 5),
-  CPlusPlus17 = (1 << 6),
-  CPlusPlus2a = (1 << 7),
-  Digraphs = (1 << 8),
-  GNUMode = (1 << 9),
-  HexFloat = (1 << 10),
-  ImplicitInt = (1 << 11),
-  OpenCL = (1 << 12)
+  C17 = (1 << 3),
+  CPlusPlus = (1 << 4),
+  CPlusPlus11 = (1 << 5),
+  CPlusPlus14 = (1 << 6),
+  CPlusPlus17 = (1 << 7),
+  CPlusPlus2a = (1 << 8),
+  Digraphs = (1 << 9),
+  GNUMode = (1 << 10),
+  HexFloat = (1 << 11),
+  ImplicitInt = (1 << 12),
+  OpenCL = (1 << 13)
 };
 
 }
 
 /// LangStandard - Information about the properties of a particular language
 /// standard.
 struct LangStandard {
   enum Kind {
public:
   bool hasLineComments() const { return Flags & frontend::LineComment; }
 
   /// isC99 - Language is a superset of C99.
   bool isC99() const { return Flags & frontend::C99; }
 
   /// isC11 - Language is a superset of C11.
   bool isC11() const { return Flags & frontend::C11; }
 
+  /// isC17 - Language is a superset of C17.
+  bool isC17() const { return Flags & frontend::C17; }
+
   /// isCPlusPlus - Language is a C++ variant.
   bool isCPlusPlus() const { return Flags & frontend::CPlusPlus; }
 
   /// isCPlusPlus11 - Language is a C++11 variant (or later).
   bool isCPlusPlus11() const { return Flags & frontend::CPlusPlus11; }
 
   /// isCPlusPlus14 - Language is a C++14 variant (or later).
   bool isCPlusPlus14() const { return Flags & frontend::CPlusPlus14; }

include/clang/Frontend/LangStandards.def

 LANGSTANDARD_ALIAS_DEPR(c11, "c1x")
 LANGSTANDARD_ALIAS_DEPR(c11, "iso9899:201x")
 
 LANGSTANDARD(gnu11, "gnu11",
              C, "ISO C 2011 with GNU extensions",
              LineComment | C99 | C11 | Digraphs | GNUMode | HexFloat)
 LANGSTANDARD_ALIAS_DEPR(gnu11, "gnu1x")
 
+// C17 modes
+LANGSTANDARD(c17, "c17",
+             C, "ISO C 2017",
+             LineComment | C99 | C11 | C17 | Digraphs | HexFloat)
+LANGSTANDARD_ALIAS(c17, "iso9899:2017")
+LANGSTANDARD(gnu17, "gnu17",
+             C, "ISO C 2017 with GNU extensions",
+             LineComment | C99 | C11 | C17 | Digraphs | GNUMode | HexFloat)
+
 // C++ modes
 LANGSTANDARD(cxx98, "c++98",
              CXX, "ISO C++ 1998 with amendments",
              LineComment | CPlusPlus | Digraphs)
 LANGSTANDARD_ALIAS(cxx98, "c++03")
 
 LANGSTANDARD(gnucxx98, "gnu++98",
              CXX, "ISO C++ 1998 with amendments and GNU extensions",

lib/Frontend/CompilerInvocation.cpp

       break;
     }
   }
 
   const LangStandard &Std = LangStandard::getLangStandardForKind(LangStd);
   Opts.LineComment = Std.hasLineComments();
   Opts.C99 = Std.isC99();
   Opts.C11 = Std.isC11();
+  Opts.C17 = Std.isC17();
   Opts.CPlusPlus = Std.isCPlusPlus();
   Opts.CPlusPlus11 = Std.isCPlusPlus11();
   Opts.CPlusPlus14 = Std.isCPlusPlus14();
   Opts.CPlusPlus17 = Std.isCPlusPlus17();
   Opts.CPlusPlus2a = Std.isCPlusPlus2a();
   Opts.Digraphs = Std.hasDigraphs();
   Opts.GNUMode = Std.isGNUMode();
   Opts.GNUInline = !Opts.C99 && !Opts.CPlusPlus;

lib/Frontend/InitPreprocessor.cpp

   if (!LangOpts.MSVCCompat && !LangOpts.TraditionalCPP)
     Builder.defineMacro("__STDC__");
   if (LangOpts.Freestanding)
     Builder.defineMacro("__STDC_HOSTED__", "0");
   else
     Builder.defineMacro("__STDC_HOSTED__");
 
   if (!LangOpts.CPlusPlus) {
-    if (LangOpts.C11)
+    if (LangOpts.C17)
+      Builder.defineMacro("__STDC_VERSION__", "201710L");
+    else if (LangOpts.C11)
       Builder.defineMacro("__STDC_VERSION__", "201112L");
     else if (LangOpts.C99)
       Builder.defineMacro("__STDC_VERSION__", "199901L");
     else if (!LangOpts.GNUMode && LangOpts.Digraphs)
       Builder.defineMacro("__STDC_VERSION__", "199409L");
   } else {
     // FIXME: Use correct value for C++20.
     if (LangOpts.CPlusPlus2a)

test/Driver/unknown-std.c

 // This file checks output given when processing C/ObjC files.
 // When user selects invalid language standard
 // print out supported values with short description.
 
 // RUN: not %clang %s -std=foobar -c 2>&1 | FileCheck --match-full-lines %s
 // RUN: not %clang -x objective-c %s -std=foobar -c 2>&1 | FileCheck --match-full-lines %s
 // RUN: not %clang -x renderscript %s -std=foobar -c 2>&1 | FileCheck --match-full-lines %s
 
 // CHECK: error: invalid value 'foobar' in '-std=foobar'
 // CHECK-NEXT: note: use 'c89', 'c90', or 'iso9899:1990' for 'ISO C 1990' standard
 // CHECK-NEXT: note: use 'iso9899:199409' for 'ISO C 1990 with amendment 1' standard
 // CHECK-NEXT: note: use 'gnu89' or 'gnu90' for 'ISO C 1990 with GNU extensions' standard
 // CHECK-NEXT: note: use 'c99' or 'iso9899:1999' for 'ISO C 1999' standard
 // CHECK-NEXT: note: use 'gnu99' for 'ISO C 1999 with GNU extensions' standard
 // CHECK-NEXT: note: use 'c11' or 'iso9899:2011' for 'ISO C 2011' standard
 // CHECK-NEXT: note: use 'gnu11' for 'ISO C 2011 with GNU extensions' standard
+// CHECK-NEXT: note: use 'c17' or 'iso9899:2017' for 'ISO C 2017' standard
+// CHECK-NEXT: note: use 'gnu17' for 'ISO C 2017 with GNU extensions' standard
 
 // Make sure that no other output is present.
 // CHECK-NOT: {{^.+$}}