[MLton-user] experimental release 20051109

[Stephen Weeks]

I tried compiling with -codegen c -profile time using the following
two versions of {Declare,}ProfileLabel on my Linux machine with gcc
3.3.5.

----------------------------------------------------------------------
#define DeclareProfileLabel(l)                  \
        void l()
#define ProfileLabel(l)                                         \
        __asm__ __volatile__ (".globl _" #l "\n_" #l ":" : : )
----------------------------------------------------------------------
#define DeclareProfileLabel(l)                                  \
	extern void l () asm (#l "_internal")
#define ProfileLabel(l)                                 \
        __asm__ __volatile__ (#l "_internal:" : : )
----------------------------------------------------------------------

Both of them failed, when trying to run the executable, with

  Max profile label is 0 -- something is wrong.

Am I doing something wrong?

Of course, everything works with what's currently in the SVN.

----------------------------------------------------------------------
#define DeclareProfileLabel(l)                                  \
        void l() __attribute__ ((alias (#l "_internal")))
#define ProfileLabel(l)                                 \
        __asm__ __volatile__ (#l "_internal:" : : )
----------------------------------------------------------------------

Since MLton's time profiling works with gcc 2.9x and 3.x, which are
the most common gcc's around, and {Declare,}ProfileLabel is very
tricky and dependent on gcc version and platform, I'm reluctant to
change them just before the release.  Also, since gcc 4.x has a new
requirement for aliasing and requires -fno-tree-ch to work (even with
new definitions of {Declare,}ProfileLabel), it seems to me like the
right solution for this release is to not change anything for all
existing platform/gcc combinations, and to only introduce new
behaviors when we encounter gcc 4.0.

So, I propose the following two changes

 1. We put tests in main.fun to add -fno-tree-ch if
    (a) we're using gcc 4.x, and
    (b) time profiling is on, and
    (c) the C codegen is being used

 2. Put an #ifdef in c-chunk.h that uses the extern void definition
    of DeclareProfileLabel if gcc version is 4.x (assuming someone has
    verified that that works with gcc 4.x).

Alternatively, we could change nothing, and simply document the
-fno-tree-ch solution, since, at least for now, the current definition
of {Declare,}ProfileLabel works with that (unless I've
misunderstood).

What do people think?