1456603 - Tup backend: audit usage of check_unchanged=True

Status: RESOLVED FIXED

(Firefox Build System :: General, enhancement)

Description

[Michael Shal [:mshal]]

For ipdl and WebIDL, we use check_unchanged=True in the rule to skip downstream rules if the output is the same (ie: if a generated .cpp file is identical to the previous run, the corresponding .o file will be skipped). This should probably also be turned on for xpidl, and possibly all GeneratedFiles. We can investigate if it's also useful for compilation or other rules as well.

Comment 1

[Michael Shal [:mshal]]

Attachment: Bug 1456603 - Enable check_unchanged=True for more rules in the tup backend;

Enabling this flag on rules that produce many small outputs (especially
header files that may trigger many other rules) can help reduce
incremental build time. It probably doesn't make sense to have this
enabled for .o files and linker rules, because those are less likely to
be unchanged when an input file changes, and are also larger so the time
to diff them can be more significant.

Review commit: https://reviewboard.mozilla.org/r/242448/diff/#index_header
See other reviews: https://reviewboard.mozilla.org/r/242448/

Comment 2

[Chris Manchester (limited bugmail, email directly)]

Comment on attachment 8974166 [details]
Bug 1456603 - Enable check_unchanged=True for more rules in the tup backend;

https://reviewboard.mozilla.org/r/242448/#review248378

Comment 3

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/c99ba2e8d166
Enable check_unchanged=True for more rules in the tup backend; r=chmanchester

Comment 4

[Cosmin Sabou [:CosminS]]

https://hg.mozilla.org/mozilla-central/rev/c99ba2e8d166