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According to MSVC manual (*1), cl.exe can skip including a header file
when that:
- contains #pragma once, or
- starts with #ifndef, or
- starts with #if ! defined.
GCC has a similar trick (*2), but it acts more stricter (e. g. there
must be _no tokens_ outside of #ifndef...#endif).
Sun C lacked #pragma once for a looong time. Oracle Developer Studio
12.5 finally implemented it, but we cannot assume such recent version.
This changeset modifies header files so that each of them include
strictly one #ifndef...#endif. I believe this is the most portable way
to trigger compiler optimizations. [Bug #16770]
*1: https://docs.microsoft.com/en-us/cpp/preprocessor/once
*2: https://gcc.gnu.org/onlinedocs/cppinternals/Guard-Macros.html
Notes:
Merged: https://github.com/ruby/ruby/pull/3023
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vm_getivar() provides fastpath for T_OBJECT by caching an index
of ivar. This patch also provides fastpath for FL_EXIVAR objects.
FL_EXIVAR objects have an each ivar array and index can be cached
as T_OBJECT. To access this ivar array, generic_iv_tbl is exposed
by rb_ivar_generic_ivtbl() (declared in variable.h which is newly
introduced).
Benchmark script:
Benchmark.driver(repeat_count: 3){|x|
x.executable name: 'clean', command: %w'../clean/miniruby'
x.executable name: 'trunk', command: %w'./miniruby'
objs = [Object.new, 'str', {a: 1, b: 2}, [1, 2]]
objs.each.with_index{|obj, i|
rep = obj.inspect
rep = 'Object.new' if /\#/ =~ rep
x.prelude str = %Q{
v#{i} = #{rep}
def v#{i}.foo
@iv # ivar access method (attr_reader)
end
v#{i}.instance_variable_set(:@iv, :iv)
}
puts str
x.report %Q{
v#{i}.foo
}
}
}
Result:
v0.foo # T_OBJECT
clean: 85387141.8 i/s
trunk: 85249373.6 i/s - 1.00x slower
v1.foo # T_STRING
trunk: 57894407.5 i/s
clean: 39957178.6 i/s - 1.45x slower
v2.foo # T_HASH
trunk: 56629413.2 i/s
clean: 39227088.9 i/s - 1.44x slower
v3.foo # T_ARRAY
trunk: 55797530.2 i/s
clean: 38263572.9 i/s - 1.46x slower
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