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

[Kyle Butt via Phabricator via llvm-commits]

iteratee marked 4 inline comments as done.
iteratee added inline comments.


================
Comment at: lib/CodeGen/MachineBlockPlacement.cpp:156
+             "Percent as integer."),
+    cl::init(2),
+    cl::Hidden);
----------------
davidxl wrote:
> Is this default value too low? Increase it 5 or 10 perhaps?
No, I think we should leave it. Now that it's a flag it's easy to change, and especially comparing with the entry frequency 2% is a big enough margin.


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Comment at: lib/CodeGen/MachineBlockPlacement.cpp:625
+  BlockFrequency Gain = A - B;
+  if (Gain.getFrequency() < (uint64_t) 1 << 32) {
+    if (EntryFreq < (uint64_t) 1 << 40) {
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davidxl wrote:
> I suppose this logic here is for rounding errors or overflow? Can you explain why the simple scaling with branch prob (in BranchProbablity.cpp) does not work?  
> 
> return  Gain > EntryFreq*ThresholdProb; 
> 
> 
I did the math, and found a way to do it simply.


https://reviews.llvm.org/D28583