YJIT: Introduce jit_putobject

[jhawthorn]

This extracts the logic previously inside gen_putobject to a more reusable helper method jit_putobject.

The motivation for this is that it both simplifies the implementation of other instructions, and other instructions can reuse the optimized behaviour for 32-bit special constants (most importantly opt_getinlinecache).

This commit also expands the optimization to use a mov directly to memory when we encounter a 32-bit immediate constant. Previously it covered fixnums and Qtrue/Qfalse, now it will cover any SPECIAL_CONST_P value which can be represented as a 32-bit immediate. Notably, this includes static symbols, and Qnil.

Sample disassembly

putobject with static symbol

:foo

Before:

  ; putobject
  55976964005d:  mov    eax, 0x84710c
  559769640062:  mov    qword ptr [rbx], rax

After:

  ; putobject
  55e4bb62105d:  mov    qword ptr [rbx], 0x84710c

getinlinecache

FOO = 123

def get_foo
  FOO
end

10.times { get_foo }

Before:

  ; opt_getinlinecache
  55bc6656b11a:  mov    eax, 0xf7
  55bc6656b11f:  mov    qword ptr [rbx], rax

After:

  ; opt_getinlinecache
  55ab1a1f111a:  mov    qword ptr [rbx], 0xf7

[maximecb]

Neat! :)