1064049 - The build system is not using the correct PGO flags when building with clang

Status: RESOLVED FIXED

(Firefox Build System :: General, enhancement)

Description

[alaviss0]

User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:34.0) Gecko/20100101 Firefox/34.0 Nightly/34.0a1
Build ID: 20140830062019

Steps to reproduce:

Build firefox with clang and have PGO enabled


Actual results:

The build system build firefox with -fprofile-use (not supported by clang, only create an warning said that the flag is not supported)


Expected results:

The build system build firefox with -fprofile-instr-generate then do the second build with -fprofile-instr-use

Ref: http://clang.llvm.org/docs/UsersManual.html#profile-guided-optimization

Comment 1

[Prasanth Ravi]

Same bug occurs with clang in OSX (Yosemite) with PGO optimization. 
I get the following warnings,

clang: warning: optimization flag '-fprofile-use' is not supported
clang: warning: optimization flag '-fprofile-correction' is not supported
clang: warning: optimization flag '-fprofile-use' is not supported
clang: warning: optimization flag '-fprofile-correction' is not supported

Comment 2

[alferpal]

Attachment: clang-pgo.patch

I managed to throw a patch that fixes clang being fed with incorrect arguments, still, there two things that I haven't figured out due tu my almost 0 knowledge of the firefox build system.

1) convert all whatever.rawdata generated by the profiling pass to .profdata using llvm-profdata merge

2)the .profdata generated in step1 need to be passed to fprofile-instr-use

Still, don't know where do that.

Comment 3

[helllamer]

Looks like, with clang-3.7.0, firefox does not build. And patch clang-pgo.patch does not help.

../../build/unix/gold/ld: error: /mnt/src/user/projects/repo/firefox-developer-hg/src/mozilla-aurora/obj-x86_64-unknown-linux-gnu/toolkit/library/../../media/mtransport/build/transportlayerloopback.i_o: requires dynamic R_X86_64_PC32 reloc against '__llvm_profile_data__ZN7sigslot9has_slotsINS_15single_threadedEE14signal_connectEPNS_22_signal_base_interfaceE' which may overflow at runtime; recompile with -fPIC
../../build/unix/gold/ld: error: /mnt/src/user/projects/repo/firefox-developer-hg/src/mozilla-aurora/obj-x86_64-unknown-linux-gnu/toolkit/library/../../media/mtransport/build/transportlayerprsock.i_o: requires dynamic R_X86_64_PC32 reloc against '__llvm_profile_data__ZN7sigslot9has_slotsINS_15single_threadedEE14signal_connectEPNS_22_signal_base_interfaceE' which may overflow at runtime; recompile with -fPIC
../../build/unix/gold/ld: error: read-only segment has dynamic relocations
... more errors ...
... and many warnings...

Comment 4

[(not currently active) Ted Mielczarek]

We're shipping PGO builds built with clang now.