Openmp parallel iterator improvements (#9493)

* More flexibility in OpenMP pragma
* Use static to constrain to compile-time annotation string
* Update changelog with OpenMP change

changelog.md

@@ -11,6 +11,12 @@
   use `editdistance.editDistance` or `editdistance.editDistanceAscii`
   instead.
 
+- The OpenMP parallel iterator \``||`\` now supports any `#pragma omp directives`
+  and not just `#pragma omp parallel for`. See [OpenMP documentation](https://www.openmp.org/wp-content/uploads/OpenMP-4.5-1115-CPP-web.pdf).
+
+  The default annotation is `parallel for`, if you used OpenMP without annotation
+  the change is transparent, if you used annotations you will have to prefix
+  your previous annotations with `parallel for`.
 
 #### Breaking changes in the standard library
 

compiler/ccgstmts.nim

@@ -557,7 +557,7 @@ proc genParForStmt(p: BProc, t: PNode) =
     initLocExpr(p, call.sons[1], rangeA)
     initLocExpr(p, call.sons[2], rangeB)
 
-    lineF(p, cpsStmts, "#pragma omp parallel for $4$n" &
+    lineF(p, cpsStmts, "#pragma omp $4$n" &
                         "for ($1 = $2; $1 <= $3; ++$1)",
                         [forLoopVar.loc.rdLoc,
                         rangeA.rdLoc, rangeB.rdLoc,

compiler/semexprs.nim

@@ -2041,11 +2041,6 @@ proc semMagic(c: PContext, n: PNode, s: PSym, flags: TExprFlags): PNode =
       result = c.graph.emptyNode
   of mOmpParFor:
     checkMinSonsLen(n, 3, c.config)
-    if n.sonsLen == 4:
-      let annotationStr = getConstExpr(c.module, semExpr(c, n[^1]), c.graph)
-      if annotationStr == nil or annotationStr.kind notin nkStrKinds:
-        localError(c.config, result[^1].info,
-          "The annotation string for `||` must be known at compile time")
     result = semDirectOp(c, n, flags)
   else:
     result = semDirectOp(c, n, flags)

lib/system.nim

@@ -2186,10 +2186,14 @@ else:
         inc(res)
 
 
-iterator `||`*[S, T](a: S, b: T, annotation=""): T {.
+iterator `||`*[S, T](a: S, b: T, annotation: static string = "parallel for"): T {.
   inline, magic: "OmpParFor", sideEffect.} =
-  ## parallel loop iterator. Same as `..` but the loop may run in parallel.
+  ## OpenMP parallel loop iterator. Same as `..` but the loop may run in parallel.
   ## `annotation` is an additional annotation for the code generator to use.
+  ## The default annotation is `parallel for`.
+  ## Please refer to the `OpenMP Syntax Reference<https://www.openmp.org/wp-content/uploads/OpenMP-4.5-1115-CPP-web.pdf>`_
+  ## for further information.
+  ##
   ## Note that the compiler maps that to
   ## the ``#pragma omp parallel for`` construct of `OpenMP`:idx: and as
   ## such isn't aware of the parallelism in your code! Be careful! Later