[llvm] [LV] Implement integer part of VPDerivedIV cost model (PR #198252)

[David Sherwood via llvm-commits]

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@@ -2797,6 +2797,86 @@ bool VPWidenIntOrFpInductionRecipe::isCanonical() const {
          getScalarType() == getRegion()->getCanonicalIVType();
 }
 
+InstructionCost VPDerivedIVRecipe::computeCost(ElementCount VF,
+                                               VPCostContext &Ctx) const {
+  // The cost model for this is modelled on expandVPDerivedIV in
+  // VPlanTransforms.cpp. In order to avoid overly pessimistic costs that can
+  // negatively affect vectorization it takes into account any expected
+  // simplifications that happen in simplifyRecipe.
+  switch (getInductionKind()) {
+  default:
+    // TODO: Compute cost for remaining kinds.
+    break;
+  case InductionDescriptor::IK_IntInduction: {
+    // There are currently no tests that expose a path where all lanes are
+    // used, so it's better to bail out for now.
+    if (!vputils::onlyFirstLaneUsed(this))
+      break;
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david-arm wrote:

Hi, if the patch doesn't get reverted I'll follow up with these review comments!

https://github.com/llvm/llvm-project/pull/198252