[llvm] [MachineOutliner] Sort by Benefit to Cost Ratio (PR #90264)

[Xuan Zhang via llvm-commits]

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@@ -0,0 +1,96 @@
+; This tests the order in which functions are outlined in MachineOutliner
+; There are TWO key OutlinedFunction in FunctionList
+;
+; ===================== First One =====================
+;   ```
+;     mov     w0, #1
+;     mov     w1, #2
+;     mov     w2, #3
+;     mov     w3, #4
+;     mov     w4, #5
+;   ```
+; It has:
+;   - `SequenceSize=20` and `OccurrenceCount=6`
+;   - each Candidate has `CallOverhead=12` and `FrameOverhead=4`
+;   - `NotOutlinedCost=20*6=120` and `OutliningCost=12*6+20+4=96`
+;   - `Benefit=120-96=24` and `Priority=120/96=1.25`
+;
+; ===================== Second One =====================
+;   ```
+;     mov     w6, #6
+;     mov     w7, #7
+;     b
+;   ```
+; It has:
+;   - `SequenceSize=12` and `OccurrenceCount=4`
+;   - each Candidate has `CallOverhead=4` and `FrameOverhead=0`
+;   - `NotOutlinedCost=12*4=48` and `OutliningCost=4*4+12+0=28`
+;   - `Benefit=120-96=20` and `Priority=48/28=1.71`
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xuanzh-meta wrote:

Yes! Thanks for catching this!

https://github.com/llvm/llvm-project/pull/90264