performance of .Primitive and .Internal

The reason .Internal(paste0(.Primitive("list")("this","and","that"),NULL)) is slower seems to be because of what Josh O'Brien guessed. Calling .Primitive("list") directly incurs some additional overhead.

You can see the effects via a simple example:

require(compiler)pl <- cmpfun({.Primitive("list")})microbenchmark(list(), .Primitive("list")(), pl())# Unit: nanoseconds#                  expr  min     lq median     uq   max neval#                list()   63   98.0  112.0  140.5   529   100#  .Primitive("list")() 4243 4391.5 4486.5 4606.0 16077   100#                  pl()   79  135.5  148.0  175.5 39108   100

That said, you're not going to be able to improve the speed of .Primitive and .Internal from the R prompt. They are both entry points to C code.

And there's no reason to try and replace a call to .Primitive with .Internal. That's recursive, since .Internal is itself a primitive.

> .Internalfunction (call)  .Primitive(".Internal")

You'll get the same slowness if you try to call .Internal "directly"... and a similar "speedup" if you compile the "direct" call.

Internal. <- function() .Internal(paste0(list("this","and","that"),NULL))Primitive. <- function() .Primitive(".Internal")(paste0("this","and","that"),NULL)cPrimitive. <- cmpfun({Primitive.})microbenchmark(Internal., Primitive., cPrimitive., times=1e4)# Unit: nanoseconds#         expr min lq median uq  max neval#    Internal.  26 27     27 28 1057 10000#   Primitive.  28 32     32 33 2526 10000#  cPrimitive.  26 27     27 27 1706 10000

The R interpreter has hardcoded optimizations for common functions, and this goes deeper than byte compiling:

> list2 <- list> list3 <- cmpfun(list2)> microbenchmark(+   list(1,2),+   list2(1,2),+   list3(1,2)+ )Unit: nanoseconds        expr min    lq    mean median    uq   max neval  list(1, 2) 576 620.5  654.53  640.0 675.5   941   100 list2(1, 2) 619 702.0 1123.43  728.0 761.0 39045   100 list3(1, 2) 617 683.0  735.83  715.5 759.0  1964   100

Here's what the SEXPs look like. Note the metadata on "list"

> .Internal(inspect(quote(list(1,2))))@23b0ed0 06 LANGSXP g0c0 [NAM(2)]   @1ed8f48 01 SYMSXP g1c0 [MARK,LCK,gp=0x4000] "list" (has value)  @2c7adf8 14 REALSXP g0c1 [] (len=1, tl=0) 1  @2c7adc8 14 REALSXP g0c1 [] (len=1, tl=0) 2

list2 is missing some metadata:

> list2 <- list> .Internal(inspect(quote(list2(1,2))))@23b1578 06 LANGSXP g0c0 [NAM(2)]   @23b0a70 01 SYMSXP g0c0 [] "list2"  @2c7ad08 14 REALSXP g0c1 [] (len=1, tl=0) 1  @2c7acd8 14 REALSXP g0c1 [] (len=1, tl=0) 2

.Primitive("list") is a more complicated expression:

> .Internal(inspect(quote(.Primitive("list")(1,2))))@297e748 06 LANGSXP g0c0 [NAM(2)]   @297d9a0 06 LANGSXP g0c0 []     @1ec4530 01 SYMSXP g1c0 [MARK,LCK,gp=0x4000] ".Primitive" (has value)    @2c7a888 16 STRSXP g0c1 [] (len=1, tl=0)      @1ed5588 09 CHARSXP g1c1 [MARK,gp=0x61] [ASCII] [cached] "list"  @2c7a858 14 REALSXP g0c1 [] (len=1, tl=0) 1  @2c7a828 14 REALSXP g0c1 [] (len=1, tl=0) 2