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Re: Use move-if-change on macro_list dependency

On 17/11/2004, at 3:08 AM, Nathan Sidwell wrote:

Geoffrey Keating wrote:
On 16/11/2004, at 4:31 AM, Nathan Sidwell wrote:
I received the attached patch from Jon Grimm, --
I've added the changelog. It does fix the problem I am seeing, and seems
good to me.

tested on powerpc64-unknown-linux-gnu with -j4 bootstrap
Does this really fix the problem, or does it just permute the Makefile and cause the underlying problem to be hidden?
(If it does fix the problem, could you explain how?)

All the other uses of move-if-changed in the makefile use the stamp file
idiom. We're using recursive makes and move-if-changed is causing
the child makes to be lied to, as the file time stamps no longer reflect
the rebuilding wavefront. The stamp idiom makes sure the rebuild wavefront
is accurate. the child makes will percieve macro_list as out of date
wrt stmp-macro_list, but the rule to rebuild that causes no change to
the file system, only changes the child make's internal state.

I've actually seen another report, from Dale, that having multiple sub-makes running inside the gcc/ directory causes other problems; he wasn't seeing anything to do with macro_list, he was failing earlier trying to build insn-recog.c (or some insn- file, anyway). So I'm quite sure that this patch doesn't fix the problem it was claimed to fix, which is that we have multiple copies of make trying to rebuild gcc/.

However, it may fix some other problem. From the description above, it saves an exec() or two, at the cost of adding an extra rule; so it's a performance patch, or possibly an unperformance patch.

If, considering the above, you still think this patch is a good idea, it's OK to commit.

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