Re: Precompiled headers

[Mike Stump <mrs at apple dot com>]

On Saturday, November 8, 2003, at 04:41 AM, Robert Vazan wrote:
> Yes, I am concerned about modify-compile-test cycle. I don't mind 
> length of
> nightly rebuild and releases.

Ah, ok.  A very important detail.

> >  Yes, in that case, we should be able
> > to get _lots_ of speed improvements.
>
> Do you mean that your project will be able to eliminate unnecessary
> rebuilds?

No, what it means is that if you rebuild, that those rebuilds will go 
faster, compile time
should be close to the amount changed + things that are dependent upon 
those things that changed.  While we don't have all the code 
implemented to do this, yet, the design so far, permits it.

> Can your code answer the question whether given object file will
> change after rebuild without actually rebuilding it? Makefiles answer 
> that
> question wrongly in most cases and that's where the waste comes from.

They change.

> If you already plan this, then I better wait for your results instead 
> of
> starting overlapping project. What do you think?

No, you don't have to wait, but use it (the compile server) as a 
starting point.  See how well it works, see what problems you find, 
report on the results you see, including the bugs.  Try your hand at 
fixing the easier ones that you find.

If you want pointers into what needs doing, see below.  The first three 
are trivial and will need doing.  0 is hard, and I am doing that now.  
3, 4, 5 and 6 need testing and maybe doing.

Unintended problems:
1   add if (server_mode) to output fragments in toplev.c
1   asm_out_file = 0 when we close it (crash on linux)
1   fix fragment end code to not ftell when asm_out_file is 0.
Laguage fidelity:
0   -D on client cmd line
1   C++: cpp macros reset/restored per fragment
      As this is done, -include is only done once, so ensure that all 
fragments are active
	 for the -include.
    Unintented smashing of data (TREE_ASM_WRITTEN) causing errors
2   Fixup overloading to be fragment aware
    #import/#pragma once files will not be included in other TUs.  See 
should_stack_file,
	reset once_only.
Asm fidelity:
3   debugging information
5   EH information
4   RTX const pool
6   Ln being ok on frag reuse
    dup .stabs "t5.cc",130,... info
    debugging info for builtins (bool:) (marked as output, undo/redo)
	IDENTIFIER_TYPENAME_P needs to be set/reset upon fragment activation 
and bewteen units.
	TREE_DEPRACATED needs to be set/reset upon fragment activation and 
bewteen units, also
	should be called
       IDENTIFIER_DEPRACATED
       cpp_hashnode->flags & NODE_POISONED
Usage:
    Streamline server starting
    Default to on (at least for testing)
Determinism:
    Return exit code after we reregister with load balancer
Scalability:
    Running out of vm
    Expiring old fragments when memory is tight
GC:
	Restore useful dynamic type checking in gt_pch_note_object.