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

Juan Manuel Martinez CaamaƱo via llvm-commits llvm-commits at lists.llvm.org
Thu Oct 10 02:33:20 PDT 2024


================
@@ -304,11 +299,62 @@ bool SIPreEmitPeephole::getBlockDestinations(
   return true;
 }
 
+namespace {
+class BranchWeightCostModel {
+  const SIInstrInfo &TII;
+  const TargetSchedModel &SchedModel;
+  BranchProbability BranchProb;
+  static constexpr uint64_t BranchNotTakenCost = 1;
+  uint64_t BranchTakenCost;
+  uint64_t ThenCyclesCost = 0;
+
+public:
+  BranchWeightCostModel(const SIInstrInfo &TII, const MachineInstr &Branch,
+                        const MachineBasicBlock &Succ)
+      : TII(TII), SchedModel(TII.getSchedModel()) {
+    assert(SchedModel.hasInstrSchedModelOrItineraries());
+
+    const MachineBasicBlock &Head = *Branch.getParent();
+    const auto *FromIt = find(Head.successors(), &Succ);
+    assert(FromIt != Head.succ_end());
+
+    BranchProb = Head.getSuccProbability(FromIt);
+    assert(!BranchProb.isUnknown());
----------------
jmmartinez wrote:

I've removed the assert and set the probability of "jumping" to the `Then` block to 0 if unknown.

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


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