[turbofan] Add single --turbo flag.

src/flag-definitions.h

Index: src/flag-definitions.h
diff --git a/src/flag-definitions.h b/src/flag-definitions.h
index 6923c6c04654f9309462ae56b3ad37d5576921b0..deaffd6be2353190d7989acb4da56efc8507a988 100644
--- a/src/flag-definitions.h
+++ b/src/flag-definitions.h
@@ -380,6 +380,9 @@ DEFINE_BOOL(omit_map_checks_for_leaf_maps, true,
             "deoptimize the optimized code if the layout of the maps changes.")
 
 // Flags for TurboFan.
+DEFINE_BOOL(turbo, false, "enable TurboFan compiler")
+DEFINE_VALUE_IMPLICATION(turbo, turbo_filter, "*")

[Michael Achenbach, 2015/04/16 11:37:21]

I assume this can be overridden and e.g. has no meaning when
--turbo_filter=something_else is used on the command line?

[Michael Starzinger, 2015/04/16 12:10:22]

Unfortunately no. The implication always wins, this means --turbo always wins.
Hence "--turbo --turbo=filter=foo" will still set the filter to "*" and
--turbo-filter will be ignored, no matter in what order the flags appear on the
command line. Totally non-intuitive. :(

[Michael Starzinger, 2015/04/16 13:56:50]

Done. OK, this is the closest I could get it to what we want. Now --turbo-filter
(almost) always wins. Whenever the FLAG_turbo_filter is still set to the default
value after all flags have been parse, then --turbo will set --turbo-filter=* as
an implication. Is this good enough? WDYT?

+DEFINE_IMPLICATION(turbo, turbo_deoptimization)
 DEFINE_STRING(turbo_filter, "~", "optimization filter for TurboFan compiler")
 DEFINE_BOOL(trace_turbo, false, "trace generated TurboFan IR")
 DEFINE_BOOL(trace_turbo_graph, false, "trace generated TurboFan graphs")