[llvm] [AMDGPU][SIPreEmitPeephole] mustRetainExeczBranch: use BranchProbability and TargetSchedmodel (PR #109818)

[Juan Manuel Martinez Caamaño via llvm-commits]

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@@ -305,10 +310,53 @@ bool SIPreEmitPeephole::getBlockDestinations(
 }
 
 bool SIPreEmitPeephole::mustRetainExeczBranch(
-    const MachineBasicBlock &From, const MachineBasicBlock &To) const {
+    const MachineBasicBlock &Head, const MachineBasicBlock &From,
+    const MachineBasicBlock &To) const {
+
+  auto FromIt = find(Head.successors(), &From);
+  assert(FromIt != Head.succ_end());
+  BranchProbability ExecNZProb = Head.getSuccProbability(FromIt);
+
   unsigned NumInstr = 0;
-  const MachineFunction *MF = From.getParent();
 
+  unsigned long ExecNZBranchCost = 0;
+  unsigned long UnconditionalBranchCost = 0;
+  unsigned long N = 0;
+  unsigned long D = 0;
+  unsigned long ThenCyclesCost = 0;
+
+  std::function<bool(const MachineInstr &)> IsProfitable =
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jmmartinez wrote:

I moved the functions into 2 classes + base since there is some payload for each cost function.

Alternatively, I can move it to 2 classes and use an `std::variant` for dispatching instead of a virtual method.

https://github.com/llvm/llvm-project/pull/109818