RFR: 8293116: Incremental JDK build could be sped up [v2]

[Jan Lahoda]

On Wed, 31 Aug 2022 20:02:46 GMT, Erik Joelsson <erikj at openjdk.org> wrote:

>> Jan Lahoda has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Reflecting review feedback.
>
> make/common/JavaCompilation.gmk line 451:
> 
>> 449:     # $$($1_VARDEPS_FILE) is used as dependency to track changes in set of
>> 450:     # list of files.
>> 451:     $$($1_COMPILE_TARGET): $$($1_SRCS) $$($1_DEPENDS) \
> 
> What's the reason for inlining this recipe into the main compilation recipe? I would think generating the modfiles file in the FILELIST rule would help reduce the noise from non source files in the prerequisites list (as the old FILELIST rule had a lot less prerequisites listed). Keeping this recipe separate also limits regeneration of the FILELIST.

I've tried to fix this in:
https://github.com/openjdk/jdk/pull/10104/commits/f1e19e8b636ddf08500a6401ce1488265f7b9446

> make/common/JavaCompilation.gmk line 456:
> 
>> 454: 		$$(call LogWarn, Compiling up to $$(words $$($1_SRCS)) files for $1)
>> 455: 		$$(eval $$(call ListPathsSafely, $1_SRCS, $$($1_FILELIST)))
>> 456: 		$$(call WriteFile, "-XDmodifiedInputs=$$? ", $$@.modfiles)
> 
> I'm not sure WriteFile is safe to use here. `$?` could potentially contain all files in `$1_SRCS`, which is why we use ListPathsSafely in the first place. This is only a problem if using make <4.0, but as long as that's not prohibited, we need to keep it working without the file function.

Is there some recommendation on how to generate what is needed? Which is:

"-XDmodifiedFiles=<list-of-files> "


I was looking at the `WriteFile` rule, and it is not clear to be what is the problem there, but I'm not very knowledgeable of the build system.

I was trying to use `ListPathsSafely`, but wasn't able to find a way that would be working.

Thanks!

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PR: https://git.openjdk.org/jdk/pull/10104