Add gpuId proc on locale

modules/internal/ChapelLocale.chpl

@@ -443,6 +443,16 @@ module ChapelLocale {
     @chpldoc.nodoc
     proc isGpu() : bool { return false; }
 
+    // if using a gpu locale return its position in the parent locale's
+    // `here.gpus` array
+    proc gpuId : int do return gpuIdImpl();
+
+    @chpldoc.nodoc
+    proc gpuIdImpl() : int {
+      halt("Can not use 'gpuId' field on a non gpu locale");
+      return -1;
+    }
+
 // Part of the required locale interface.
 // Commented out because presently iterators are statically bound.
 //    iter getChildren() : locale  {

modules/internal/localeModels/gpu/LocaleModel.chpl

@@ -262,6 +262,10 @@ module LocaleModel {
     }
 
     override proc isGpu() : bool { return true; }
+
+    override proc gpuIdImpl() : int {
+      return sid;
+    }
   }
 
   const chpl_emptyLocaleSpace: domain(1) = {1..0};

test/gpu/native/multiGPU/gpuId.chpl

@@ -0,0 +1,5 @@
+var n = 0;
+for gpu in here.gpus do on gpu {
+  assert(gpu.gpuId == n);
+  n += 1;
+}

test/gpu/native/multiLocale/gpuId.chpl

@@ -0,0 +1,7 @@
+coforall loc in Locales do on loc {
+  var n = 0;
+  for gpu in here.gpus do on gpu {
+    assert(gpu.gpuId == n);
+    n += 1;
+  }
+}

test/gpu/nongpu/gpuId.chpl

@@ -0,0 +1 @@
+writeln(here.gpuId);

test/gpu/nongpu/gpuId.good

@@ -0,0 +1 @@
+gpuId.chpl:1: error: halt reached - Can not use 'gpuId' field on a non gpu locale