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

[Matt Arsenault via llvm-commits]

Juan Manuel Martinez =?utf-8?q?Caamaño?= <juamarti at amd.com>
Message-ID:
In-Reply-To: <llvm.org/llvm/llvm-project/pull/109818 at github.com>


================
@@ -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());
----------------
arsenm wrote:

But does it matter that it underflowed? The logic will still come out to return false? This check is not required for correctness 

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