[PATCH] D28583: CodeGen: Allow small copyable blocks to "break" the CFG.

[Kyle Butt via Phabricator via llvm-commits]

iteratee added inline comments.


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Comment at: lib/CodeGen/MachineBlockPlacement.cpp:642
+  // increases fallthrough.
+  if (SuccSuccs.size() == 0)
+    return true;
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davidxl wrote:
> davidxl wrote:
> > I assume this is loop back edge source block. You need a test case to cover it.
> test case for this?
It's not just a back edge. I added a test case.


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Comment at: lib/CodeGen/MachineBlockPlacement.cpp:671
+  BranchProbability PProb = MBPI->getEdgeProbability(BB, Succ);
+  BlockFrequency P = BBFreq * PProb;
+  // At this point, we don't know which block would be chosen instead of Succ.
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davidxl wrote:
> Add a short cut here with comments:
> 
> // If P is not larger, the best successor selection loop will eventually select C, not Succ (as it is not profitable to do so).
> if (P <= Qout)
>    return false;
If we weren't estimating Qout, I'd agree. Instead we'll skip calling this altogether if we know that we won't use the result.


https://reviews.llvm.org/D28583