[Issue 11881] New: -betterC switch suffers from bit rot

[d-bugmail at puremagic.com]

https://d.puremagic.com/issues/show_bug.cgi?id=11881

           Summary: -betterC switch suffers from bit rot
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody at puremagic.com
        ReportedBy: bugzilla at digitalmars.com


--- Comment #0 from Walter Bright <bugzilla at digitalmars.com> 2014-01-07 18:57:47 PST ---
Adam D. Ruppe writes:

I find the -betterC switch to be totally useless. If you are just toying,
there's no module info anyway:

extern(C) {
    void _d_run_main() {} // why is this required now????
    void* _d_dso_registry;

    void _start() {

    }
}

dmd -c *.d -defaultlib= -debuglib=
gcc -m32 *.o -nostdlib

success. Add "struct Test{}" and:

Error: ModuleInfo not found. object.d may be incorrectly installed or corrupt.

OK, add -betterC:

Error: TypeInfo not found. object.d may be incorrectly installed or corrupt,
compile with -v switch


If you do use an object.d with it defined to get past the compiler, it doesn't
help much as the linker complains anyway:

test.o:(.data._D20TypeInfo_S4test4Test6__initZ+0x0): undefined reference to
`_D15TypeInfo_Struct6__vtblZ'


So my verdict is -betterC is pretty useless. If it got past the TypeInfo stuff
the same way it gets past ModuleInfo though, then we'd be cooking with gas.
That potentially gives a language that is legitimately a better C. But without
structs, bah.

This is a filthy hack, but it is easy to change this in the compiler. (Isn't
-betterC a filthy hack in the first place anyway :) )

In

Expression *Type::getTypeInfo(Scope *sc)

Add
    if(global.params.betterC)
        return NULL;

right to the top.

And same for struct decl

void TypeInfoStructDeclaration::toDt(dt_t **pdt)
{
    if(global.params.betterC)
        return;


Then it compiles with the struct! ~5 KB executable, two line object.d.


....but adding some methods to the struct complain about missing ModuleInfo
again. Looks like it wants to do assert(this !is null); and the assert thing
takes a module info reference.

Ugh.... that said, adding:

    void _d_assert_msg() {}
    void _d_assertm() {}
    void* _D4test12__ModuleInfoZ;

to my extern(C) boilerplate did manage to work - structs with postblits and
dtors yay! - and trimmed the exe down to 1.3K.

Maybe -betterC can stop outputting those references too and then we'd really be
cooking.

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