[SystemZ][z/OS] enable trigraphs by default on z/OS

[abhina.sreeskantharajan]

Summary

This patch enables trigraphs on z/OS.

[hubert.reinterpretcast]

clang/lib/Frontend/CompilerInvocation.cpp

2787–2789

If going with an integrated update to the existing sentences, both of the original sentences would require an update (not just the first one). The first sentence is also meant to describe GCC's behavior, for which I am not sure there's a statement to be made for GCC on z/OS. I suggest to add an additional sentence instead.

2791

I would like to point out that processing trigraphs when most platforms don't would be a portability concern. Clang appears to mitigate this somewhat with warnings.

clang/test/Frontend/trigraphs.cpp

8

Do we know if -fno-trigraphs is meaningfully functional on z/OS? I believe trigraph usage might need to be replaced to use digraphs in the system headers before using -fno-trigraphs can be expected to work in a real user application.

[fanbo-meng]

Can you modify clang/test/Frontend/trigraphs.cpp and clang/test/Lexer/cxx1z-trigraphs.cpp ? These tests are assuming trigraphs are disabled by -std=gnu++11 -fms-compatibility -std=c++1z, and it won't be the case here because on z/OS trigraphs are still enabled when these options are present.

[abhina.sreeskantharajan]

Thanks Hubert and Fanbo for reviewing. I updated the comment to Hubert's suggestion, and updated both testcases as requested.

[abhina.sreeskantharajan]

clang/lib/Frontend/CompilerInvocation.cpp

2791

Unfortunately we can't move away from this because the system headers currently use trigraphs. But we will definitely look into whether we can update these headers to not be dependent on trigraphs and improve portability.

clang/test/Frontend/trigraphs.cpp

8

With the current system headers, compiling with -fno-trigraphs would not work in a user application. As mentioned above, we will look into whether we can remove this dependency.

[hubert.reinterpretcast]

clang/test/Lexer/cxx1z-trigraphs.cpp

33

This strategy duplicates the trigraphs-enabled behaviour checks three times.

Plain -verify can be used along with a macro instead (without such duplication). This also allows the explicit -fno-trigraphs case to be added with little cost.

Pseudo-code:

// RUN: ...
// RUN: ... -ftrigraphs -DENABLED_TRIGRAPHS=1
// RUN: ... -fno-trigraphs -DENABLED_TRIGRAPHS=0

#ifdef __MVS__
#ifndef ENABLED_TRIGRAPHS
#define ENABLED_TRIGRAPHS 1
#endif
#endif

#if !ENABLED_TRIGRAPHS
// ...
#else
// ...
#endif

[abhina.sreeskantharajan]

Thanks Hubert for the suggestion. I've updated the lit test.

[hubert.reinterpretcast]

LGTM with suggested changes.

clang/test/Lexer/cxx1z-trigraphs.cpp

19

Intentional whitespace disappeared.

24

This seems to have changed in a weird way?

[abhina.sreeskantharajan]

Thanks for catching that. I fixed up the testcase.

clang/lib/Frontend/CompilerInvocation.cpp

if (const Arg *A = Args.getLastArg(OPT_fms_compatibility_version)) {
     if (VT.tryParse(A->getValue()))
       Diags.Report(diag::err_drv_invalid_value) << A->getAsString(Args)
                                                 << A->getValue();
     Opts.MSCompatibilityVersion = VT.getMajor() * 10000000 +
                                   VT.getMinor().getValueOr(0) * 100000 +
                                   VT.getSubminor().getValueOr(0);
   }
 
   // Mimicking gcc's behavior, trigraphs are only enabled if -trigraphs
   // is specified, or -std is set to a conforming mode.
   // Trigraphs are disabled by default in c++1z onwards.
-  Opts.Trigraphs = !Opts.GNUMode && !Opts.MSVCCompat && !Opts.CPlusPlus17;
+  // For z/OS, trigraphs are enabled by default (without regard to the above).
+  Opts.Trigraphs =
+      (!Opts.GNUMode && !Opts.MSVCCompat && !Opts.CPlusPlus17) || T.isOSzOS();
   Opts.Trigraphs =
       Args.hasFlag(OPT_ftrigraphs, OPT_fno_trigraphs, Opts.Trigraphs);
 
   Opts.DollarIdents = Args.hasFlag(OPT_fdollars_in_identifiers,
                                    OPT_fno_dollars_in_identifiers,
                                    Opts.DollarIdents);
   Opts.PascalStrings = Args.hasArg(OPT_fpascal_strings);
   Opts.setVtorDispMode(

clang/test/Frontend/trigraphs.cpp

 // RUN: %clang_cc1 -DSTDCPP11 -std=c++11 -verify -fsyntax-only %s
 // RUN: %clang_cc1 -DSTDGNU11 -std=gnu++11 -verify -fsyntax-only %s
 // RUN: %clang_cc1 -DSTDGNU11TRI -ftrigraphs -std=gnu++11 -verify -fsyntax-only %s
 // RUN: %clang_cc1 -DSTDCPP17 -std=c++1z -verify -fsyntax-only %s
 // RUN: %clang_cc1 -DSTDCPP17TRI -ftrigraphs -std=c++1z -verify -fsyntax-only %s
 // RUN: %clang_cc1 -DMSCOMPAT -fms-compatibility -std=c++11 -verify -fsyntax-only %s
+// RUN: %clang_cc1 -DNOTRI -fno-trigraphs -verify -fsyntax-only %s
 
 void foo() {
 #if defined(NOFLAGS) || defined(STDCPP11) || defined(STDGNU11TRI) || \
-    defined(STDCPP17TRI)
+    defined(STDCPP17TRI) || (defined(__MVS__) && !defined(NOTRI))
   const char c[] = "??/n"; // expected-warning{{trigraph converted to '\' character}}
-#elif defined(STDGNU11) || defined(STDCPP17) || defined(MSCOMPAT)
+#elif defined(STDGNU11) || defined(STDCPP17) || defined(MSCOMPAT) || \
+    defined(NOTRI)
   const char c[] = "??/n"; // expected-warning{{trigraph ignored}}
 #else
 #error Not handled.
 #endif
 }

clang/test/Lexer/cxx1z-trigraphs.cpp

 // RUN: %clang_cc1 -std=c++1z %s -verify
-// RUN: %clang_cc1 -std=c++1z %s -ftrigraphs -fsyntax-only 2>&1 | FileCheck --check-prefix=TRIGRAPHS %s
+// RUN: %clang_cc1 -std=c++1z %s -verify -ftrigraphs -DENABLED_TRIGRAPHS=1
+// RUN: %clang_cc1 -std=c++1z %s -verify -fno-trigraphs -DENABLED_TRIGRAPHS=0
 
-??= define foo ; // expected-error {{}} expected-warning {{trigraph ignored}}
+#ifdef __MVS__
+#ifndef ENABLED_TRIGRAPHS
+#define ENABLED_TRIGRAPHS 1
+#endif
+#endif
 
-static_assert("??="[0] == '#', ""); // expected-error {{failed}} expected-warning {{trigraph ignored}}
+??= define foo ;
+
+static_assert("??="[0] == '#', "");
 
 // ??/
-error here; // expected-error {{}}
+error here;
 
-// Note, there is intentionally trailing whitespace two lines below.
-// TRIGRAPHS: :[[@LINE+1]]:{{.*}} backslash and newline separated by space
-// ??/  
-error here; // expected-error {{}}
+// Note, there is intentionally trailing whitespace one lines below.
+// ??/
+error here;
+
+#if !ENABLED_TRIGRAPHS
+// expected-error@11 {{}} expected-warning@11 {{trigraph ignored}}
+// expected-error@13 {{}} {failed}} expected-warning@13 {{trigraph ignored}}
+// expected-error@16 {{}}
+// expected-error@20 {{}}
+#else
+// expected-warning@11 {{trigraph converted}}
+// expected-warning@13 {{trigraph converted}}
+// expected-warning@19 {{backslash and newline separated by space}}
+#endif