[PATCH] D10717: Enhance loop rotation with existence of profile data in MachineBlockPlacement pass.

[David Li via llvm-commits]

davidxl added inline comments.

================
Comment at: lib/CodeGen/MachineBlockPlacement.cpp:920
@@ +919,3 @@
+    // 1. If the tail node has only one successor, then we will get an
+    //    additional jmp instruction. So the cost here is (MisfetchCost +
+    //    JumpInstCost) * tail node frequency.
----------------
The situation is 

TailBB->currentChainHead
TailBB->OtherSucessor

After rotation, TailBB->OtherSuccessor may be a fall through, so there is no need for a jump for that case. If OtherSuccessor is inside the chain, then a jmp is definitely needed.


http://reviews.llvm.org/D10717