[OpenMP] Nim symbol interpolation support

[mratsim]

Similar to emit pragma it would be very useful to have Nim symbol interpolation support in OpenMP annotations.

Currently the following code:

import sequtils, macros

var x = toSeq(1..1000)

let ompsize = x.len
let ompthreshold = 800

for i in `||`(0, x.len - 1, "if(`ompthreshold` < `ompsize`)"):
  x[i] += 2

echo x[0]

Generates:

// ... removing seq initialization
	T7_ = (x_wFAR9b1Cy8ShaaTQG2FH9c7g ? x_wFAR9b1Cy8ShaaTQG2FH9c7g->Sup.len : 0);
	ompsize_89bqUwA9bOswTIcWIVyaG9cfw = T7_;
	ompthreshold_XaMtJe9ajIFJ9btvwMO3AaEw = ((NI) 800);
	T8_ = (x_wFAR9b1Cy8ShaaTQG2FH9c7g ? x_wFAR9b1Cy8ShaaTQG2FH9c7g->Sup.len : 0);
	#pragma omp parallel for if(`ompthreshold` < `ompsize`)
for (i = ((NI) 0); i <= (NI)(T8_ - ((NI) 1)); ++i)	{
		x_wFAR9b1Cy8ShaaTQG2FH9c7g->data[i] += ((NI) 2);
	}
	nimZeroMem((void*)T10_, sizeof(tyArray_nHXaesL0DJZHyVS07ARPRA));
	T10_[0] = nimIntToStr(x_wFAR9b1Cy8ShaaTQG2FH9c7g->data[((NI) 0)]);
	echoBinSafe(T10_, 1);

[alaviss]

I think you should substitute ompthreshold and ompsize in the C code with their actual name...

[mratsim]

@alaviss I can't easily, that's the whole point of the feature request.

[mratsim]

Here is a workaround for 0.19 that will also mangles names in case of nested OpenMP loops.

In templates exportc doesn't catch the constants #9366 hence the omp_suffix proc must keep track of the last suffix generated.

# omp_mangling.nim
import random
from strutils import toHex

var mangling_rng {.compileTime.} = initRand(0x1337DEEDBEAF)
var current_suffix {.compileTime.} = ""

proc omp_suffix*(genNew: static bool = false): static string =
  ## genNew:
  ##   if false, return the last suffix
  ##   else return a fresh one

  if genNew:
    current_suffix = mangling_rng.rand(high(uint32)).toHex
  result = current_suffix

# omp_threshold.nim

import sequtils, macros
import ../laser/openmp/omp_mangling

var x = toSeq(1..1000)

template plus2(s: var seq[int]) =
  const
    suffix = omp_suffix(genNew = true)
    ompsize_Csym = "ompsize_" & suffix
    ompthreshold_Csym = "ompthreshold_" & suffix
    ompAnnotation = "if(" & ompthreshold_Csym & " < " & ompsize_Csym & ")"

  # We can't use {.exportc: ompsize_Csym.} directly due to #9366
  let ompsize {.exportc: "ompsize_" & omp_suffix(genNew = false).}= x.len
  let ompthreshold {.exportc: "ompthreshold_" & omp_suffix(genNew = false).}= 800

  for i in `||`(0, x.len - 1, ompAnnotation):
    x[i] += 2

plus2(x)
plus2(x)

echo x[0]

Generated C code

// ...........
	T7_ = (x_wFAR9b1Cy8ShaaTQG2FH9c7g ? x_wFAR9b1Cy8ShaaTQG2FH9c7g->Sup.len : 0);
	ompsize_00000000CB2E7BAE = T7_;
	ompthreshold_00000000CB2E7BAE = ((NI) 800);
	T8_ = (x_wFAR9b1Cy8ShaaTQG2FH9c7g ? x_wFAR9b1Cy8ShaaTQG2FH9c7g->Sup.len : 0);
	#pragma omp parallel for if(ompthreshold_00000000CB2E7BAE < ompsize_00000000CB2E7BAE)
for (i = ((NI) 0); i <= (NI)(T8_ - ((NI) 1)); ++i)	{
		x_wFAR9b1Cy8ShaaTQG2FH9c7g->data[i] += ((NI) 2);
	}
	T10_ = (x_wFAR9b1Cy8ShaaTQG2FH9c7g ? x_wFAR9b1Cy8ShaaTQG2FH9c7g->Sup.len : 0);
	ompsize_000000009280FB6D = T10_;
	ompthreshold_000000009280FB6D = ((NI) 800);
	T11_ = (x_wFAR9b1Cy8ShaaTQG2FH9c7g ? x_wFAR9b1Cy8ShaaTQG2FH9c7g->Sup.len : 0);
	#pragma omp parallel for if(ompthreshold_000000009280FB6D < ompsize_000000009280FB6D)
for (i_2 = ((NI) 0); i_2 <= (NI)(T11_ - ((NI) 1)); ++i_2)	{
		x_wFAR9b1Cy8ShaaTQG2FH9c7g->data[i_2] += ((NI) 2);
	}
	nimZeroMem((void*)T13_, sizeof(tyArray_nHXaesL0DJZHyVS07ARPRA));
	T13_[0] = nimIntToStr(x_wFAR9b1Cy8ShaaTQG2FH9c7g->data[((NI) 0)]);
	echoBinSafe(T13_, 1);