8387377: Compilation is very slow when --module-path contains many Automatic Modules and ALL-MODULE-PATH is used.

[lahodaj]

Automatic modules have requires transitive directives to all other automatic modules. When computing the transitive readability set, javac follows all these directives, for all the modules. When there's a high number of automatic modules, this can take a long time, as for each automatic module, javac does the full loop through all the other automatic modules.

This PR is attempting to improve the situation in two ways:

• the transitive readability computation is computed directly for automatic modules, avoiding the repeated analysis of automatic module dependencies.
• the pre-existing transitive readability cache is filled and used a bit more directly.

The enclosed test which uses 1_000 automatic modules is running in ~1s on my computer with this change; times out without it.

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 ⚠️ Found trailing period in issue title for 8387377: Compilation is very slow when --module-path contains many Automatic Modules and ALL-MODULE-PATH is used.

Issue

• JDK-8387377: Compilation is very slow when --module-path contains many Automatic Modules and ALL-MODULE-PATH is used. (Bug - P4)

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[davidalayachew]

Thank you thank you so much! This will make development much easier. Plus, having this work will make migration much easier for other projects too.

Automatic Modules are a critical first step for projects that want to dip their toes into going fully modular. Adding the Automatic-Module-Name to a jar's MANIFEST.MF is an easy first step to get most of the benefits of going modular, and an important stabilizing point. But, that also requires the ALL-MODULE-PATH to make it usable from the start. Without it, it just takes too much effort to enumerate every transitive Automatic Module that is not being pulled in by your direct dependencies.