[llvm] [LV][VPlan] Implement VPlan-based cost for exit condition. (PR #125640)

[Florian Hahn via llvm-commits]

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@@ -7238,45 +7238,6 @@ LoopVectorizationPlanner::precomputeCosts(VPlan &Plan, ElementCount VF,
     }
   }
 
-  /// Compute the cost of all exiting conditions of the loop using the legacy
-  /// cost model. This is to match the legacy behavior, which adds the cost of
-  /// all exit conditions. Note that this over-estimates the cost, as there will
-  /// be a single condition to control the vector loop.
-  SmallVector<BasicBlock *> Exiting;
-  CM.TheLoop->getExitingBlocks(Exiting);
-  SetVector<Instruction *> ExitInstrs;
-  // Collect all exit conditions.
-  for (BasicBlock *EB : Exiting) {
-    auto *Term = dyn_cast<BranchInst>(EB->getTerminator());
-    if (!Term)
-      continue;
-    if (auto *CondI = dyn_cast<Instruction>(Term->getOperand(0))) {
-      ExitInstrs.insert(CondI);
-    }
-  }
-  // Compute the cost of all instructions only feeding the exit conditions.
-  for (unsigned I = 0; I != ExitInstrs.size(); ++I) {
-    Instruction *CondI = ExitInstrs[I];
-    if (!OrigLoop->contains(CondI) ||
-        !CostCtx.SkipCostComputation.insert(CondI).second)
-      continue;
-    InstructionCost CondICost = CostCtx.getLegacyCost(CondI, VF);
-    LLVM_DEBUG({
-      dbgs() << "Cost of " << CondICost << " for VF " << VF
-             << ": exit condition instruction " << *CondI << "\n";
-    });
-    Cost += CondICost;
-    for (Value *Op : CondI->operands()) {
-      auto *OpI = dyn_cast<Instruction>(Op);
-      if (!OpI || any_of(OpI->users(), [&ExitInstrs, this](User *U) {
-            return OrigLoop->contains(cast<Instruction>(U)->getParent()) &&
-                   !ExitInstrs.contains(cast<Instruction>(U));
-          }))
-        continue;
-      ExitInstrs.insert(OpI);
----------------
fhahn wrote:

I am not sure, `for (unsigned I = 0; I != ExitInstrs.size(); ++I) {` should evaluate `.size()` on each iteration, given that it may change in the loop?


https://github.com/llvm/llvm-project/pull/125640