[Gm2] git commits/pushes to master

[Gaius Mulley]

Hi,

I'm in the process of pushing git commits on the master branch which
include two new options:

   -fm2-plugin and -fno-m2-plugin

which insert a back end plugin to detect whether an exception is going
to be executed at run-time.  Also added are some better exception
descriptions (for loop/begin/end identified and assignment of procedure
function return value overflow).  The plugin will generate a warning
should an exception be executed and it deduces this by examining the
first basic block of each procedure and detecting whether a call to any
exception handler in M2RTS is invoked.

This is performed as a plugin as it is inserted at the end of
optimisation.  Thus the constant folding, constant propagation etc will
all have occurred which gives the gcc backend the opportunity to
eliminate any dead code, thus increasing the likelihood of compile time
detection of the handler invocation.

The -fm2-plugin option is best used with -O2 or -O3 as it can exploit
the control flow and variable analysis optimisation knowledge.

Once I've sorted out some libtool automake problems these changes will
be git pushed and ready for testing.

hope these are useful,


regards,
Gaius