Re: [epsilon-devel] How to write a simple code generation which is not terrible

[Luca Saiu]

-- Sorry.  This is the hand-optimized version (I wrote the unoptimized
version twice by mistake):

instruction push-variable (?n 0 1, ?n 0 1 2 3 4 5)
  code
    int i;
    const int depth = JITTER_ARGN0;
    const int index = JITTER_ARGN1;
    jitter_int res;
    JITTER_PUSH_UNSPECIFIED_MAINSTACK();
    for (i = 0; i < depth; i ++)
      JITTER_STATE_RUNTIME_FIELD(env) = JITTER_STATE_RUNTIME_FIELD(env)->upper;
    res = jitter_state_runtime.env->values [index];
    JITTER_TOP_MAINSTACK() = res;
  end
end

And the specialized instruction disassembly is the three-instruction
sequence I copied:
    0x00007f56eb77e5e1 48 89 75 08              movq   %rsi,0x8(%rbp)
    0x00007f56eb77e5e5 49 8b 71 10              movq   0x10(%r9),%rsi
    0x00007f56eb77e5e9 48 83 c5 08              addq   $0x8,%rbp

It's easy to see that this version closely matches what the behavior of
machine-generated code obtaining the the stack effect separately from
assigning results to the appropriate l-values.

Awesome.

-- 
Luca Saiu
* GNU epsilon:           http://www.gnu.org/software/epsilon
* My personal web site:  http://ageinghacker.net

I support everyone's freedom of mocking any opinion or belief, no
matter how deeply held, with open disrespect and the same unrelented
enthusiasm of a toddler who has just learned the word "poo".

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