proper order of initialization for .global. variables

compiler/ccgstmts.nim

@@ -53,7 +53,7 @@ proc genSingleVar(p: BProc, a: PNode) =
   var targetProc = p
   var immediateAsgn = a.sons[2].kind != nkEmpty
   if sfGlobal in v.flags:
-    targetProc = p.module.initProc
+    targetProc = p.module.preInitProc
     assignGlobalVar(targetProc, v)
     genObjectInit(targetProc, cpsInit, v.typ, v.loc, true)
   else:

compiler/cgen.nim

@@ -859,6 +859,7 @@ proc genInitCode(m: BModule) =
   
   app(prc, genSectionStart(cpsLocals))
   app(prc, m.initProc.s[cpsLocals])
+  app(prc, m.preInitProc.s[cpsLocals])
   app(prc, genSectionEnd(cpsLocals))
 
   app(prc, genSectionStart(cfsTypeInit1))
@@ -875,10 +876,12 @@ proc genInitCode(m: BModule) =
     app(prc, genSectionEnd(i))
   
   app(prc, genSectionStart(cpsInit))
+  app(prc, m.preInitProc.s[cpsInit])
   app(prc, m.initProc.s[cpsInit])
   app(prc, genSectionEnd(cpsInit))
 
   app(prc, genSectionStart(cpsStmts))
+  app(prc, m.preInitProc.s[cpsStmts])
   app(prc, m.initProc.s[cpsStmts])
   if optStackTrace in m.initProc.options and not m.PreventStackTrace:
     app(prc, deinitFrame(m.initProc))
@@ -916,6 +919,7 @@ proc rawNewModule(module: PSym, filename: string): BModule =
   result.typeInfoMarker = initIntSet()
   result.initProc = newProc(nil, result)
   result.initProc.options = gOptions
+  result.preInitProc = newProc(nil, result)
   initNodeTable(result.dataCache)
   result.typeStack = @[]
   result.forwardedProcs = @[]

compiler/cgendata.nim

@@ -93,6 +93,10 @@ type
     headerFiles*: TLinkedList # needed headers to include
     typeInfoMarker*: TIntSet  # needed for generating type information
     initProc*: BProc          # code for init procedure
+    preInitProc*: BProc       # code executed before the init proc
+                              # used for initialization code for
+                              # .global. variables
+                              # (or instantiated generic variables)
     typeStack*: TTypeSeq      # used for type generation
     dataCache*: TNodeTable
     forwardedProcs*: TSymSeq  # keep forwarded procs here

doc/manual.txt

@@ -3267,7 +3267,7 @@ but are used to override the settings temporarily. Example:
   {.pop.} # restore old settings
 
 
-Register pragma
+register pragma
 ---------------
 The `register`:idx: pragma is for variables only. It declares the variable as
 ``register``, giving the compiler a hint that the variable should be placed
@@ -3277,6 +3277,22 @@ though and for good reasons: Often they do a better job without it anyway.
 In highly specific cases (a dispatch loop of an bytecode interpreter for
 example) it may provide benefits, though.
 
+global pragma
+---------------
+The `global`:idx pragma can be applied to a variable within a proc to instruct
+the compiler to store it in a global location and initialize it once at program
+startup.
+
+.. code-block:: nimrod
+proc isHexNumber(s: string): bool =
+  var pattern {.global.} = re"[0-9a-fA-F]+"
+  result = s.match(pattern)
+
+When used within a generic proc, a separate unique global variable will be
+created for each instantiation of the proc. The order of initialization of
+the created global variables within a module is not defined, but all of them
+will be initialized after any top-level variables in their originating module
+and before any variable in a module that imports it. 
 
 DeadCodeElim pragma
 -------------------

tests/run/globalaux.nim

@@ -0,0 +1,15 @@
+type 
+  TObj*[T] = object
+    val*: T
+
+var
+  totalGlobals* = 0
+
+proc makeObj[T](x: T): TObj[T] =
+  totalGlobals += 1
+  result.val = x
+
+proc globalInstance*[T]: var TObj[T] =
+  var g {.global.} = when T is int: makeObj(10) else: makeObj("hello")
+  result = g
+

tests/run/globalaux2.nim

@@ -0,0 +1,4 @@
+import globalaux
+
+echo "in globalaux2: ", globalInstance[int]().val
+

tests/run/tglobal.nim

@@ -0,0 +1,16 @@
+discard """
+  file: "toop1.nim"
+  output: "in globalaux2: 10\ntotal globals: 2\nint value: 100\nstring value: second"
+"""
+
+import globalaux, globalaux2
+
+echo "total globals: ", totalGlobals
+
+globalInstance[int]().val = 100
+echo "int value: ", globalInstance[int]().val
+
+globalInstance[string]().val = "first"
+globalInstance[string]().val = "second"
+echo "string value: ", globalInstance[string]().val
+