[PATCH] D21663: [MBP] Enhance cost based branch prob threshold computation to handle general control flows

[Dehao Chen via llvm-commits]

danielcdh added inline comments.

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Comment at: lib/CodeGen/MachineBlockPlacement.cpp:610
@@ +609,3 @@
+    //         (C)                 (D)
+    //  (D) is a degenerated case of (C) where Pred1 does not exist. In (D),
+    //  Let
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You mean in (C), right?

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Comment at: lib/CodeGen/MachineBlockPlacement.cpp:624
@@ +623,3 @@
+    //  order for BB->Succ to be selected, we must have F1 > F2 + F3. So the
+    //  backward probability threshold is (backward checking igores other
+    //  predecessors other than Pred2):
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This is a little confusing, I think the condition should be:

F1 > max(2*F3, F2)

So when checking Pred1, the backward threhold should be 0.66, when checking Pred2, the backward threshold should be 0.5?

But for the current implementation, I tried all testcase, and some other testcases with different triangle-diamond combination, and it always gives me optimal solution.


http://reviews.llvm.org/D21663