Debug options for IRHydra (deoptimizations tracing)

[puzrin]

It would be nice to have more options for deoptimizations debug: http://mrale.ph/irhydra/2/

1. --print-opt-code
2. patch for IRHydra2

Is it possible to enable those by default? If not, is it possible to have ready dev binaries, that can be installed easy via nvm and so on. Building dev configuration manually is not convenient.

[trevnorris]

1. haven't done any performance analysis
2. must wait for upgrade to V8 3.24.39

[puzrin]

Can i hope to see IRHydra2 support in nearest releases? AFAIK v8 is now upgraded to acceptable version.

[bnoordhuis]

--print-opt-code only works when V8 is compiled with ENABLE_DISASSEMBLER. That flag is disabled in release builds unless v8_enable_disassembler=1 is set.

Is it worth it to enable it by default? It will make the binary a few hundred kB bigger and add a few seconds to the build.

[puzrin]

I use node to write high-speed modules. Last example is https://github.com/nodeca/pako , that is just 1.3 time slower than native C code. Problem with such modules is lack of easily accessible tools.

IMHO, good instruments will motivate developpers to do interesting things. I'll be fine with ANY one-click solution, that will not require manually edit configs and rebuild node froum src. Special official dev build will be ok, for example.

[trevnorris]

IRHydra2 can be used with current master. You only need the build option if
you want to be able to see the assembly code generated by Crankshaft. If
viewing the IR generated by Hydrogen, code paths, deoptimizations, etc. are
enough then you need no additional build option.

[puzrin]

IMHO, viewing assembly src is useful, to better understand if optimized code still contains unboxing calls or not. This also helps to locate problem places, because IRHydra2 not always can find exact string number in js, that caused deoptimization.

[jasnell]

@trevnorris @bnoordhuis ... any further thoughts on this one?

[trevnorris]

I know the disassembler was enabled in the io.js build, but I forget if it was done in Node.js.

[jasnell]

Ok, so the question then becomes: should we enable it in joyent/node master or v0.12 going forward or simply pick it up in the converged stream?

[bnoordhuis]

I think @indutny did that in #7639? Or was that reverted?

[jasnell]

Don't believe so. Will close this then!