[m-rev.] for review: fix smart recompilation bug

[Simon Taylor]

On 04-Jul-2001, Fergus Henderson <fjh at cs.mu.OZ.AU> wrote:
> On 04-Jul-2001, Simon Taylor <stayl at cs.mu.OZ.AU> wrote:
> > 
> > Use a timestamp file mechanism similar to that used for `.int' files 
> > to avoid rechecking whether a module needs to be recompiled on each
> > mmake if no used interfaces have changed.
> 
> Hmm... your change means that this timestamp file mechanism is used
> even when smart recompilation is not enabled.  This will slow down
> compilation in the case when smart recompilation is not enabled.
> Compilation will be slower because
> 
> 	(1) More files need to be read
> 	(2) More files need to be written
> 	(3) The directory is bigger, because it contains more files
> 
> These effects will be more pronounced if file I/O is expensive,
> e.g. when using NFS file systems.
> 
> Have you measured how much effect this change has on compilation
> speed when compiling over NFS?
> 
> Have you considered enabling the new mechanism only when
> `--smart-recompilation' is used?

I did think about this, but my intention is that smart recompilation
will be the default sooner rather than later. It's not worth adding
the extra complexity to conditionally use timestamps.

We'll also be able to do something about the proliferation of timestamp
files when mmake is part of the compiler.

Simon.
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