The mechanism by which PGO builds are kicked off is kinda wonky.
The MOZ_PGO environment variable is recognized by configure and setting
it will result in MOZ_PGO being defined in substs. In addition, the
build backend (previously client.mk, now Makefile.in) also recognizes
MOZ_PGO (from mozconfig or environment) and takes appropriate action.
In-tree mozconfigs set MOZ_PGO via mk_add_options. mk_add_options
is intended as a mechanism to inject state into client.mk and the
make-based build system.
In addition, there is code in mozharness (unchanged by this commit)
that sets MOZ_PGO if appropriate.
A PGO build configuration is different from a non-PGO build
configuration. Therefore a make-centric environment variable to
control PGO is not ideal. Instead, this should be defined as a
configure-time flag and the build invocation should key off that.
This commit normalizes in-tree mozconfigs to set MOZ_PGO via
ac_add_options and updates the PGO documentation to recommend
this method.
MozReview-Commit-ID: k6AZyJuXjs
--HG--
extra : rebase_source : b1a6348611eba08dd67ec938cca5586fbe8e6910
extra : source : 25c7ebc7c44dd253f421b6de3d0337635d0c99d0
Gabriele Svelto
Gregory Szorc