[PATCH] D110018: [lld-macho] Speed up markLive()

[Vy Nguyen via Phabricator via llvm-commits]

oontvoo marked an inline comment as done.
oontvoo added inline comments.


================
Comment at: lld/MachO/MarkLive.cpp:97-120
+      // TODO:  we can avoid iterating inputSections multiple times.
+      //
+      // S_ATTR_LIVE_SUPPORT sections are live if they point _to_ a live
+      // section.
+      // Process them in a second pass.
+      if (!skip) {
+        for (size_t i = start; i <= end; ++i) {
----------------
int3 wrote:
> I'm kind of suspicious of this. It's marking sections as live based on the liveness of other sections, which are concurrently being marked as live. Depending on the order of writes, it may incorrectly conclude that a certain live section X is not live, and therefore not mark the sections that X points to as live.
Good point! (kind of surprised not a lot of tests were failing ...)



================
Comment at: lld/MachO/MarkLive.cpp:171-172
+
+    if (start < idx || end >= size) {
+      if (idx < size) {
+        start = end = idx;
----------------
int3 wrote:
> i'm kind of confused here. why are we comparing `start` to `idx` -- isn't `start` an index into the `size` array of jobs, whereas `idx` is the index of the `Task` vector of size `poolSize`? seems like we're comparing numbers on different scales...
> 
> same thing for `idx` and `size`
"idx" is the index of the Task vector, yes but it correlates to where its work items are:

So the division of labour is like this:

```
Task[0] : start=0, end = start + d -1 = d -1 
Task[1] : start=d, end = d + d - 1
Task[2]: start = d + d, end = d + d + d -1
....
Task[n]: start = n * d, end = start + d -1.
```


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D110018/new/

https://reviews.llvm.org/D110018