add test for C trigraphs

[duncan]

main = print "??)"

If we compile the above -fvia-C then some gcc versions report:

/tmp/ghc6084_0/ghc6084_0.hc:99:30:
     warning: trigraph ??) ignored, use -trigraphs to enable

This should make us nervous.

According to the GCC manual if we were ever to use -std=c89 or any of the official C standard compliance modes (ie non-GNU) then we would get standard C (cpp) trigraph behavior.

We should therefore add a codeGen/should_run test to make sure that the above program does always print "??)" and never "]". This test only needs to be run for the -fvia-C 'ways', optc etc.

It's not an immediate priority but it may trip someone up in future when porting or if we make unregisterised C code more standards compliant and start using one of the official -std= modes. It is unlikely to hit us but if it ever did it'd be a real pain to debug.

[duncan]

For info on gcc's treatment of trigraphs see  http://gcc.gnu.org/onlinedocs/cpp/Initial-processing.html

[igloo]

Good point; I've added a test cg063. It would make sense to avoid generating them too.

Based on what gcc -Wall says, "??)" is a trigraph but "?" "?)" isn't.

[duncan]

Replying to igloo:

Based on what gcc -Wall says, "??)" is a trigraph but "?" "?)" isn't.

Yes, the GCC page above says:

The nine trigraphs and their replacements are

          Trigraph:       ??(  ??)  ??<  ??>  ??=  ??/  ??'  ??!  ??-
          Replacement:      [    ]    {    }    #    \    ^    |    ~

It's also got some hints on how to avoid them, though it also seems to indicate that they're not portable.