968845 - Win32 PGO builds pass -LTCG:PGINSTRUMENT to cl, but -LTCG is a linker option

Status: RESOLVED WORKSFORME

(Firefox Build System :: General, defect)

Description

[Emanuel Hoogeveen [:ehoogeveen]]

While looking at a build log for a recent win32 PGO build I noticed that cl prints the following warning:

cl : Command line warning D9002 : ignoring unknown option '-LTCG:PGINSTRUMENT'

And indeed, this flag is passed to cl during a lot of build steps - but -LTCG is a linker option. Since I couldn't find -LTCG:PGOPTIMIZE anywhere, for a while I thought PGO might be entirely broken, but it seems we do pass -LTCG:PGINSTRUMENT to the linker while linking xul and use -LTCG:PGUPDATE further down, so I think this is probably just a cosmetic issue.

Still, it's confusing at best and there's still a chance passing the flag to cl means we're not passing it to the linker in places we intend to, so it would be nice to fix. As an aside, cl also prints the following other warnings:

cl : Command line warning D9002 : ignoring unknown option '-OP'
cl : Command line warning D9002 : ignoring unknown option '-OT'
cl : Command line warning D9002 : ignoring unknown option '-O:'
cl : Command line warning D9002 : ignoring unknown option '-OR'
cl : Command line warning D9002 : ignoring unknown option '-OE'
cl : Command line warning D9002 : ignoring unknown option '-OF'

Comment 1

[(not currently active) Ted Mielczarek]

I don't see this anywhere in a current PGO build log:
https://treeherder.mozilla.org/logviewer.html#?job_id=22264168&repo=mozilla-inbound

Maybe we fixed it at some point?

Comment 2

[Emanuel Hoogeveen [:ehoogeveen]]

Yeah, I didn't see this locally anymore either when I tested it again recently. I did see several instances of "MSIL .netmodule or module compiled with /GL found; restarting link with /LTCG; add /LTCG to the link command line to improve linker performance", but I'm not sure if that's a PGO thing, or how much difference it would make to fix. Either way, not this bug.

Comment 3

[(not currently active) Ted Mielczarek]

That happens if you wind up linking without -LTCG but you link in an object file that was compiled with -GL. It's pretty harmless, but if we can track down where it comes from we could fix it.