asynchronous_exceptions

[Richard Henderson <rth at redhat dot com>]

What, exactly, does this get used for in the java runtime?

As far as I can tell, the implementation of this in the generic part
of the compiler is completely broken, and has quite possibly never
Really Worked.

Further, I find indications in gcc/java/decl.c that you want to throw
from inside signal handlers, which will not work properly with dwarf2
EH as-is.  (We'd need cpu+os specific code to help us interpret the
signal stack frame.)

What I'm thinking of doing is putting in a language-specific hook
allowing the front end to indicate whether a may_trap_p insn may
throw an exception, and if so, what set of exceptions might be seen.
(The exact interface for the later I havn't thought about too much.)

This cleanup will allow two things: One, we'll be able to create
correct control-flow graphs for things besides calls.  Two, I'll
be able to remove NOTE_INSN_EH_REGION notes during the main body
of compilation and rely entirely on REG_EH_REGION tags.  This will
in turn simplify several optimization passes.


r~