Building and Iterating

[Conrad Meyer]

On Fri, Jun 1, 2018 at 1:59 PM, Lev Serebryakov <lev at freebsd.org> wrote:
> On 01.06.2018 23:02, Ryan Stone wrote:
>
>>> 3.  If the boostrap toolchain needs to be built in the normal case, only
>>> target the ARCH being requested.  I understand that we "want" a CC
>>> installed that targets all architectures and this is something I agree with.
>>
>> Has anybody instrumented the build to determine how much time this
>> would actually save?  Before trying to optimize the build we need to
>> be sure that we're actually targetting the right optimizations.
>  LLVM build could easily take one hour to be built on rather modern system.
>
>  My VM to build NanoBSD images has 8GiB of RAM (1/4 of total physical
> RAM), 4 cores of i7 (out of 4 cores / 8 threads) and resides on SSD
> (SATA one). Build WITH cross-toolchain AND world toolchain is about 2.5
> hours and build WITHOUT ANY toolchain (using host's one as
> cross-compiler) is less than a hour.

Unfortunately, you aren't actually measuring the impact of Sean's #3 —
which proposes eliminating cross-compilers from Clang *when building
Clang is actually desired or required.*  It isn't clear that the
additional cross-compiler backends add significant overhead to the
total Clang build time, which includes a lot of shared code, like C
and C++ parsing, generic optimization code, etc.

Ryan's just asking for someone to measure that to justify the change.

Best,
Conrad