[PATCH] SectionMemoryManager is not a JITMemoryManager

[David Tweed]

Hi,

I haven't had time to do more than skim the patch, but one thing is that I
notice there aren't any changes to any of the tests. I know that we've
unfortunately got a situation where several of the MCJIT using tests just
copy and paste whatever memory management code lli was using at the time so
they easily end up out-of-sync. If after this patch is applied they still
need updating I'll have a go at it, although it might be preferable if
someone more knowledgeable has a look... (I just about know how to what
needs to be done one ARM, but I may well not understand the other supported
but less mainstream architectures.)

Will try to come up with other comments on the patch today,

Cheers,
Dave

-----Original Message-----
From: llvm-commits-bounces at cs.uiuc.edu
[mailto:llvm-commits-bounces at cs.uiuc.edu] On Behalf Of Filip Pizlo
Sent: 04 May 2013 20:37
To: llvm-commits at cs.uiuc.edu
Subject: [PATCH] SectionMemoryManager is not a JITMemoryManager

This patch cleans up the relationship between RTDyldMemoryManager,
JITMemoryManager, and EngineBuilder.

As I understand it, JITMemoryManager is meant to go away at some point, and
RTDyldMemoryManager is not meant to be predestined to have to support all of
the things that JITMemoryManager had; it may have some of the same things,
but also maybe some new things, and probably not all of the old things.

But right now EngineBuilder doesn't know anything about RTDyldMemoryManager
and assumes that JITMemoryManager is the way memory is managed in both MCJIT
and the old JIT.  This means that if you want to pass an RTDyldMemoryManager
to the MCJIT via the EngineBuilder API, you have to actually create a
JITMemoryManager and stub out a *bunch* of methods.  SectionMemoryManager
does this, for example: SectionMemoryManager is a subtype of
JITMemoryManager that cannot actually be used as a JITMemoryManager, except
passing it through EngineBuilder so that MCJIT can use it as an
RTDyldMemoryManager. :-/

This patch attempts to fix the problem:

- EngineBuilder now knows that RTDyldMemoryManager and JITMemoryManager are
different but similar things.  It knows that if you set a JITMemoryManager,
then it can be used for the MCJIT.  It knows that an RTDyldMemoryManager can
also be used for the MCJIT, but cannot be used for old JIT.  It will ensure
that you cannot set both at the same time since that would be confusing
(setting one overrides the other).

- SectionMemoryManager is no longer a subtype of JITMemoryManager, and no
longer has a ton of stub unimplemented methods.

- lli and various tests are changed to know that a SectionMemoryManager is
not a JITMemoryManager.

This is a change to the C++ API, and I actually don't know that the policies
on this are!  But I hope that this is something that we can change, since it
kills some gnarly code and concentrates whatever little ugliness remains
into EngineBuilder (it's only ugly because it has to know that there are two
kinds of ways of saying that you want to manager memory yourself).

-Filip