Enable extended debugging symbols to including better tracking.

Enable extended debugging symbols to including better tracking.

Adding -fvar-tracking-assignments and -fvar-tracking to improve
tracking of variables and assignments. While mostly useful when
compiling with optimisations on (-O flags), it does help with clang
(and later gccs) which are doing many optimisations all the time.
(It does sometimes default to on when compiling with -O flags.)

From http://gcc.gnu.org/onlinedocs/gcc/Debugging-Options.html
> -fvar-tracking
>  Run variable tracking pass. It computes where variables are stored
>  at each position in code. Better debugging information is then
>  generated (if the debugging information format supports this
>  information).
>
>  It is enabled by default when compiling with optimization (-Os, -O,
>  -O2, ...), debugging information (-g) and the debug info format
>  supports it.
>
> -fvar-tracking-assignments
>  Annotate assignments to user variables early in the compilation and
>  attempt to carry the annotations over throughout the compilation
>  all the way to the end, in an attempt to improve debug information
>  while optimizing. Use of -gdwarf-4 is recommended along with it.
>
>  It can be enabled even if var-tracking is disabled, in which case
>  annotations are created and maintained, but discarded at the end.

Committed: https://crrev.com/9f7cb7480b85d868fb3420b960018d9137c9954a
Cr-Commit-Position: refs/heads/master@{#296662}

[mithro-old, 2014-09-23 17:12:18]

mithro@mithis.com changed reviewers:
+ thakis@chomium.org, thestig@chromium.org

[mithro-old, 2014-09-23 17:15:03]

Heyo,

Just cleaning up some old CLs and came across the whole reason I started
enabling debug fission stuff in the first place.

With landing https://codereview.chromium.org/198363002/ and it seeming to have
stuck now, this CL now becomes possible.

Tim 'mithro' Ansell

[Lei Zhang, 2014-09-23 23:58:05]

thestig@chromium.org changed reviewers:
+ thakis@chromium.org
- thakis@chomium.org

[Lei Zhang, 2014-09-23 23:58:05]

lgtm

https://codereview.chromium.org/362183003/diff/40001/build/common.gypi
File build/common.gypi (right):

https://codereview.chromium.org/362183003/diff/40001/build/common.gypi#newcod...
build/common.gypi:3566: '-fvar-tracking-assignments', '-fvar-tracking',
Do we need to explicitly pass -fvar-tracking? The man page says it's "enabled by
default when compiling with optimization ..." We seem to meet all the
requirements.

[Nico, 2014-09-23 23:59:58]

Does clang implement these? Does this still make sense?

[mithro-old, 2014-09-24 01:14:34]

I'll check but I do believe they are implemented (but my be a nop). While
var tracking is enabled by default when building with higher optimisation
levels, it's actually still useful on the lower one where it isn't normally
enabled (specially when arguments are passed in registers). Var tracking
also further enhances the macro stuff in the other patch and is recommended
to be turned on by -g3 (these two patches use to be one before I split
them).

Tim 'mithro' Ansell
On 24 Sep 2014 09:59, <thakis@chromium.org> wrote:

> Does clang implement these? Does this still make sense?
>
> https://codereview.chromium.org/362183003/
>

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[mithro-old, 2014-09-25 04:55:52]

The CQ bit was checked by mithro@mithis.com

[commit-bot: I haz the power, 2014-09-25 04:56:20]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/362183003/40001

[commit-bot: I haz the power, 2014-09-25 05:57:03]

Committed patchset #3 (id:40001) as f67db0067a578a8e7a02a111e5bbac0d34b5feb2

[commit-bot: I haz the power, 2014-09-25 05:57:53]

Patchset 3 (id:??) landed as
https://crrev.com/9f7cb7480b85d868fb3420b960018d9137c9954a
Cr-Commit-Position: refs/heads/master@{#296662}

[mithro-old, 2014-09-25 06:16:00]

A revert of this CL (patchset #3 id:40001) has been created in
https://codereview.chromium.org/602023002/ by mithro@mithis.com.

The reason for reverting is: Breaks with

FAILED: /b/build/goma/gomacc
../../third_party/llvm-build/Release+Asserts/bin/clang -MMD -MF
obj/third_party/libwebp/enc/libwebp_enc.config.o.d -DV8_DEPRECATION_WARNINGS
-D_FILE_OFFSET_BITS=64 -DCHROMIUM_BUILD -DCR_CLANG_REVISION=216630
-DCOMPONENT_BUILD -DTOOLKIT_VIEWS=1 -DUI_COMPOSITOR_IMAGE_TRANSPORT -DUSE_AURA=1
-DUSE_ASH=1 -DUSE_PANGO=1 -DUSE_CAIRO=1 -DUSE_GLIB=1
-DUSE_DEFAULT_RENDER_THEME=1 -DUSE_LIBJPEG_TURBO=1 -DUSE_X11=1
-DUSE_CLIPBOARD_AURAX11=1 -DENABLE_ONE_CLICK_SIGNIN -DENABLE_PRE_SYNC_BACKUP
-DUSE_XI2_MT=2 -DENABLE_REMOTING=1 -DENABLE_WEBRTC=1 -DENABLE_PEPPER_CDMS
-DENABLE_CONFIGURATION_POLICY -DENABLE_NOTIFICATIONS -DUSE_UDEV
-DENABLE_EGLIMAGE=1 -DENABLE_TASK_MANAGER=1 -DENABLE_EXTENSIONS=1
-DENABLE_PLUGINS=1 -DENABLE_SESSION_SERVICE=1 -DENABLE_THEMES=1
-DENABLE_AUTOFILL_DIALOG=1 -DENABLE_BACKGROUND=1 -DENABLE_GOOGLE_NOW=1
-DCLD_VERSION=2 -DCLD2_DATA_SOURCE=static -DENABLE_FULL_PRINTING=1
-DENABLE_PRINTING=1 -DENABLE_SPELLCHECK=1 -DENABLE_CAPTIVE_PORTAL_DETECTION=1
-DENABLE_APP_LIST=1 -DENABLE_SETTINGS_APP=1 -DENABLE_MANAGED_USERS=1
-DENABLE_MDNS=1 -DENABLE_SERVICE_DISCOVERY=1 -DENABLE_LOAD_COMPLETION_HACKS=1
-DUSE_NSS=1 -DDYNAMIC_ANNOTATIONS_ENABLED=1 -DWTF_USE_DYNAMIC_ANNOTATIONS=1
-D_DEBUG -D_GLIBCXX_DEBUG=1 -Igen -I../../third_party/libwebp -fstack-protector
--param=ssp-buffer-size=4 -Werror -pthread -fno-strict-aliasing
-Wno-unused-parameter -Wno-missing-field-initializers -fvisibility=hidden -pipe
-fPIC -Wno-reserved-user-defined-literal -Xclang -load -Xclang
/b/build/slave/Linux_Builder__dbg_/build/src/third_party/llvm-build/Release+Asserts/lib/libFindBadConstructs.so
-Xclang -add-plugin -Xclang find-bad-constructs -fcolor-diagnostics
-B/b/build/slave/Linux_Builder__dbg_/build/src/third_party/binutils/Linux_x64/Release/bin
-Wheader-hygiene -Wno-char-subscripts -Wno-unneeded-internal-declaration
-Wno-covered-switch-default -Wstring-conversion -Wno-c++11-narrowing
-Wno-deprecated-register -Wno-format -Wno-unused-result -m64 -march=x86-64 -O0
-g -gdwarf-4 -fvar-tracking-assignments -fvar-tracking -funwind-tables
-gsplit-dwarf -Wno-undefined-bool-conversion -Wno-tautological-undefined-compare
  -c ../../third_party/libwebp/enc/config.c -o
obj/third_party/libwebp/enc/libwebp_enc.config.o
clang: error: unknown argument: '-fvar-tracking-assignments'
clang: error: unknown argument: '-fvar-tracking'


See
http://build.chromium.org/p/chromium.linux/builders/Linux%20Builder%20%28dbg%...
for more info..