Remove rint from jsmath library. NFC

[sbc100]

We use __builtin_rint (which lowers to a single f64.nearest
instruction) when compiling the musl version of rint.c so there there is
no need to use a JS call for this case.

[sbc100]

I updated this change to only effect rint which is clearly not necessary.

[kripken]

Hmm, I am not certain the new code is smaller, as unless I am doing something wrong, even though rint.c just does __builtin_rint, it doesn't turn into a single instruction. My testcase:

#include <emscripten.h>

int main(int argc, char **argv) {
  double x = double(argc + 1000) / double(argc + 100);
  return __builtin_rint(x);
}

emcc -O3 --profiling leads to

 (func $main (param $0 i32) (param $1 i32) (result i32)
  (local $2 f64)
  (if
   (f64.lt
    (f64.abs
     (local.tee $2
      (f64.nearest
       (f64.div
        (f64.convert_i32_s
         (i32.add
          (local.get $0)
          (i32.const 1000)
         )
        )
        (f64.convert_i32_s
         (i32.add
          (local.get $0)
          (i32.const 100)
         )
        )
       )
      )
     )
    )
    (f64.const 2147483648)
   )
   (then
    (return
     (i32.trunc_f64_s
      (local.get $2)
     )
    )
   )
  )
  (i32.const -2147483648)
 )

Ignoring the division etc., it looks like rint is not a single instruction but f64.nearest, abs, lt, trunc operations?

[sbc100]

rint does compile to single instruction:

$ ar x ./cache/sysroot/lib/wasm64-emscripten/libc.a rint.o
$ wasm-objdump -d -r -x rint.o
...
000059 func[0] <rint>:
 00005a: 20 00                      | local.get 0
 00005c: 9e                         | f64.nearest
 00005d: 0b                         | end

[sbc100]

The rest of the complixity in your example I think comes from the conversion from double to int because your are returning and double from your main function.

If I do this I see the expected results:

$ cat test.c
extern double x;

int main(int argc, char **argv) {
  x = __builtin_rint(x);
}
$ ./emcc -Os test.c -c
$ dump test.o
000043 func[0] <__main_argc_argv>:
 000044: 41 00                      | i32.const 0
 000046: 41 00                      | i32.const 0
 000048: 2b 03 80 80 80 80 00       | f64.load 3 0
           00004a: R_WASM_MEMORY_ADDR_LEB 1 <x>
 00004f: 9e                         | f64.nearest
 000050: 39 03 80 80 80 80 00       | f64.store 3 0
           000052: R_WASM_MEMORY_ADDR_LEB 1 <x>
 000057: 41 00                      | i32.const 0
 000059: 0b                         | end

[kripken]

Oh, you're right, I missed the other conversion, sorry...