[ruby-core:98762] [Ruby master Bug#16941] MJIT doesn't identify Struct kind of instruction

Issue #16941 has been updated by abhsha (Abhishek Sharma).


Hello K0kubun,

Here is the revised script
```
def my_method
    a_struct = Struct.new(:a).new
    a_struct.a = "a"
    puts "Inside this Method"
end

3.times{ puts "=="; my_method; puts "==" }
```

Output with --jit-min-calls=1
```
ruby --jit-save-temps --disable-gems --jit-min-calls=1 --jit-verbose=2 --jit-wait test.rb
MJIT: CC defaults to /tool/pandora64/bin/gcc
MJIT: tmp_dir is /tmp
Creating precompiled header
Starting process: /tool/pandora64/bin/gcc /tool/pandora64/bin/gcc -w -Wfatal-errors -fPIC -shared -w -pipe -O3 -o /tmp/_ruby_mjit_hp23581u0.h.gch /tool/pandora64/.package/ruby-2.6.0/include/ruby-2.6.0/x86_64-linux/rb_mjit_min_header-2.6.0.h
start compilation: block in <main>@test.rb:7 -> /tmp/_ruby_mjit_p23581u0.c
Starting process: /tool/pandora64/bin/gcc /tool/pandora64/bin/gcc -w -Wfatal-errors -fPIC -shared -w -pipe -O3 -o /tmp/_ruby_mjit_p23581u0.o /tmp/_ruby_mjit_p23581u0.c -c -Wl,--compress-debug-sections=zlib -nostartfiles -nodefaultlibs -nostdlib
Starting process: /tool/pandora64/bin/gcc /tool/pandora64/bin/gcc -shared -Wfatal-errors -fPIC -shared -w -pipe -O3 -o /tmp/_ruby_mjit_p23581u0.so /tmp/_ruby_mjit_p23581u0.o -Wl,--compress-debug-sections=zlib -nostartfiles -nodefaultlibs -nostdlib
JIT success (119.4ms): block in <main>@test.rb:7 -> /tmp/_ruby_mjit_p23581u0.c
==
start compilation: [e-mail]:1 -> /tmp/_ruby_mjit_p23581u1.c
Starting process: /tool/pandora64/bin/gcc /tool/pandora64/bin/gcc -w -Wfatal-errors -fPIC -shared -w -pipe -O3 -o /tmp/_ruby_mjit_p23581u1.o /tmp/_ruby_mjit_p23581u1.c -c -Wl,--compress-debug-sections=zlib -nostartfiles -nodefaultlibs -nostdlib
Starting process: /tool/pandora64/bin/gcc /tool/pandora64/bin/gcc -shared -Wfatal-errors -fPIC -shared -w -pipe -O3 -o /tmp/_ruby_mjit_p23581u1.so /tmp/_ruby_mjit_p23581u1.o -Wl,--compress-debug-sections=zlib -nostartfiles -nodefaultlibs -nostdlib
JIT success (176.5ms): [e-mail]:1 -> /tmp/_ruby_mjit_p23581u1.c
start compilation: a=@test.rb:2 -> /tmp/_ruby_mjit_p23581u2.c
MJIT warning: Skipped to compile unsupported instruction: opt_call_c_function
JIT failure (0.0ms): a=@test.rb:2 -> /tmp/_ruby_mjit_p23581u2.c
Inside this Method
==
==
start compilation: a=@test.rb:2 -> /tmp/_ruby_mjit_p23581u3.c
MJIT warning: Skipped to compile unsupported instruction: opt_call_c_function
JIT failure (0.0ms): a=@test.rb:2 -> /tmp/_ruby_mjit_p23581u3.c
Inside this Method
==
==
start compilation: a=@test.rb:2 -> /tmp/_ruby_mjit_p23581u4.c
MJIT warning: Skipped to compile unsupported instruction: opt_call_c_function
JIT failure (0.0ms): a=@test.rb:2 -> /tmp/_ruby_mjit_p23581u4.c
Inside this Method
==
Stopping worker thread
Successful MJIT finish
```

From the documentation, I understand on 1st (jit-min-calls) call a method gets queued to be "JITed", and since I'm using --jit-wait, it waits for the method to get JIT-compiled. The only problem here is that it doesn't consider if a process has been attempted to get JITed before and has failed to do so. Therefore it attempts to recompile again and again.

I have a more greedy thought, is it possible to have a mechanism to persist the JITed methods and load on a later point of time? This could be useful for creating fast gems without the need to use the C interface to write code. Also, it can be a useful scenario, where the same code runs for very large number of times. For Example, delivering software to the client, where he is just interested in running the software as a black box and get desired output.

Thanks,
Abhishek

----------------------------------------
Bug #16941: MJIT doesn't identify Struct kind of instruction
https://bugs.ruby-lang.org/issues/16941#change-86120

* Author: abhsha (Abhishek Sharma)
* Status: Feedback
* Priority: Normal
* Assignee: k0kubun (Takashi Kokubun)
* ruby -v: 2.6.0p0 (2018-12-25 revision 66547) [x86_64-linux]
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN
----------------------------------------
MJIT does not identify Struct instructions and gives a warning while compiling to C.

Example: 
def my_method
    1.times do
        a_struct = Struct.new(:a).new
        a_struct.a = "a"
    end
end

my_method

$: ruby --jit-save-temps --jit-min-calls=1 --disable-gems --jit --jit-verbose=2 --jit-wait test.rb

output:
start compilation: a=@test.rb:3 -> /tmp/_ruby_mjit_p30696u2.c
MJIT warning: Skipped to compile unsupported instruction: opt_call_c_function
JIT failure (0.0ms): a=@test.rb:3 -> /tmp/_ruby_mjit_p30696u2.c

Are structs not recognised by JIT compiler? 
We have this call in our programs many number of times (~ 10^6), it attempts every time and fails. Can this be a cause of programs to get slower with --jit enabled ? 



-- 
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