[PATCH] [lld][Core] Implement parallel_for_each

[Shankar Kalpathi Easwaran]

Implement a non-recursive version as per davide/ruiu.


http://reviews.llvm.org/D8348

Files:
  include/lld/Core/Parallel.h

Index: include/lld/Core/Parallel.h
===================================================================
--- include/lld/Core/Parallel.h
+++ include/lld/Core/Parallel.h
@@ -295,7 +295,16 @@
 #else
 template <class Iterator, class Func>
 void parallel_for_each(Iterator begin, Iterator end, Func func) {
-  // TODO: Make this parallel.
+  TaskGroup tg;
+  const ptrdiff_t minParallelSizeForEach = 1024;
+  int64_t length = distance(begin, end);
+  int64_t taskSize = (length < minParallelSizeForEach)
+                         ? length
+                         : length / minParallelSizeForEach;
+  while (taskSize <= distance(begin, end)) {
+    tg.spawn([=, &func, &tg] { std::for_each(begin, begin + taskSize, func); });
+    begin += taskSize;
+  }
   std::for_each(begin, end, func);
 }
 #endif

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