[PATCH] [lld][Core] Implement parallel_for_each

[Shankar Kalpathi Easwaran]

================
Comment at: include/lld/Core/Parallel.h:300
@@ +299,3 @@
+  const ptrdiff_t minParallelSizeForEach = 1024;
+  int64_t length = distance(begin, end);
+  int64_t taskSize = (length < minParallelSizeForEach)
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ruiu wrote:
> Does this compile without std::?
compiles/runs fine for me.

================
Comment at: include/lld/Core/Parallel.h:303
@@ +302,3 @@
+                         ? length
+                         : length / minParallelSizeForEach;
+  while (taskSize <= distance(begin, end)) {
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ruiu wrote:
> This expression doesn't make sense again. You divide length of the array with minSize, which is equal to how many minSize chunks in the array. It's not a task size.
> 
> Let's make this simple as a starter. Just set 1024 to taskSize unconditionally. That's probably large enough. You may still have to run a test with that number, though.
will change. we cannot set taskSize to 1024 unconditionally if the length < 1024.

http://reviews.llvm.org/D8348

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