I've been wondering whether the ocaml compiler does any sort of
parameter passing optimizations for data structures, e.g. stack
allocating, or destructuring them when it can determine their scope
does not escape the call. My first conclusion is that it does for
tuples only, but I wanted to see what others might know.
I wrote a number of simple test programs that each pass 6 arguments
through 2 levels of functions by a number of means (main calls foo 1M
times, foo calls bar once). For 1M iterations, the times I saw
(optimized) are posted below.
It looks like the case of passing parameters in a tuple doesn't
allocate (since the number of minor words is the same as the
positional parameters case). However, it still seems to run more than
an order of magnitude slower so perhaps it loses the benefits of
register allocation (?).
Warren
let bar a b c d e f =
a + b + c + d + e + f
minor_words: 7950
promoted_words: 2251
major_words: 2266
minor_collections: 1
major_collections: 0
heap_words: 61440
heap_chunks: 1
top_heap_words: 61440
live_words: 2266
live_blocks: 354
free_words: 59174
free_blocks: 1
largest_free: 59174
fragments: 0
compactions: 0
real0m0.860s
user0m0.835s
sys 0m0.017s
let bar (a, b, c, d, e, f) =
a + b + c + d + e + f
minor_words: 7950
promoted_words: 2251
major_words: 2266
minor_collections: 1
major_collections: 0
heap_words: 61440
heap_chunks: 1
top_heap_words: 61440
live_words: 2266
live_blocks: 354
free_words: 59174
free_blocks: 1
largest_free: 59174
fragments: 0
compactions: 0
real0m11.067s
user0m10.942s
sys 0m0.037s
let bar (Foo(a, b, c, d, e, f)) =
a + b + c + d + e + f
minor_words: 7000224061
promoted_words: 2251
major_words: 2266
minor_collections: 213629
major_collections: 0
heap_words: 61440
heap_chunks: 1
top_heap_words: 61440
live_words: 2266
live_blocks: 354
free_words: 59174
free_blocks: 1
largest_free: 59174
fragments: 0
compactions: 0
real0m17.443s
user0m17.176s
sys 0m0.089s
let bar {a=a; b=b; c=c; d=d; e=e; f=f} =
a + b + c + d + e + f
minor_words: 7000223886
promoted_words: 2251
major_words: 2266
minor_collections: 213629
major_collections: 0
heap_words: 61440
heap_chunks: 1
top_heap_words: 61440
live_words: 2266
live_blocks: 354
free_words: 59174
free_blocks: 1
largest_free: 59174
fragments: 0
compactions: 0
real0m16.314s
user0m16.167s
sys 0m0.059s
let bar ?(a=0) ?(b=0) ?(c=0) ?(d=0) ?(e=0) ?(f=0) () =
a + b + c + d + e + f
minor_words: 12002946309
promoted_words: 2251
major_words: 2266
minor_collections: 366300
major_collections: 0
heap_words: 61440
heap_chunks: 1
top_heap_words: 61440
live_words: 2266
live_blocks: 354
free_words: 59174
free_blocks: 1
largest_free: 59174
fragments: 0
compactions: 0
real0m33.036s
user0m32.648s
sys 0m0.156s
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