Re: [patch] Build generator programs in a build directory

[Zack Weinberg <zack at codesourcery dot com>]

Kelley Cook <kcook@gcc.gnu.org> writes:

> Zack Weinberg said:
>>  You can correct this by leaving the (elaborated) definition of
>>  fancy_abort in gcov.c, or by adding rules to the Makefile to buld
>>  two copies of errors.o, one for build one for host (see the existing
>>  treatment of rtl.c) And if you like to rename all the object files
>>  that are built only for the build machine, so that it's harder to
>>  mak this mistake in the future, that would be nice.
>
> This patch takes Zack's suggestion and goes one step further and puts 
> all the generated programs into a separate build/ directory.  The only 
> slight loss is that the few dozen gen* files will no longer be part of 
> the bootstrap comparison process as they are no longer copied into the 
> stageN directories.
>
> It should be mostly uncontroversial, though I would like Paolo to peruse 
> it in case it has some ramifications for his toplevel bootstrap plan. 

I agree that this should be mostly uncontroversial; I have no
objection, but would also like to hear Paolo's comment.  I'd also like
to suggest that if this goes through, you remove the "build-" prefix
from the basenames of various object files, as this is now redundant.

> Doing this has some additional future benefits, since the gen*.o files 
> are in a separate directory with a few tweaks they no longer would be 
> required to be deleted and thereby forcibly rebuilt for each stage. 
...
> The only disadvantage that I foresee will be that we will miss the case 
> of a hypothetical complier bug that causes it to only miscompile one of 
> the gen*.c in such a way that it generates a different insn-* file, but 
> not end up misgenerating anything else in the rest of the compiler or 
> the testsuite.  That seems to be is a remote possibilty.  I think that 
> potential loss will be seen as a fair trade for greater developer 
> efficiency.

There *have* been bugs in the past where the gen*.c have been
miscompiled, but like you, I doubt that those bugs would have failed
to show up elsewhere.  And I certainly like the idea of making
bootstrap go faster.

zw