[llvm] [LV] Support argmin/argmax with strict predicates. (PR #170223)

[Florian Hahn via llvm-commits]

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@@ -1120,6 +1122,128 @@ bool VPlanTransforms::handleMaxMinNumReductions(VPlan &Plan) {
   return true;
 }
 
+/// For argmin/argmax reductions with strict predicates, convert the existing
+/// FindLastIV reduction to a new UMin reduction of a wide canonical IV. If the
+/// original IV was not canonical, a new canonical wide IV is added, and the
+/// final result is scaled back to the original IV.
+static bool handleFirstArgMinArgMax(VPlan &Plan,
+                                    VPReductionPHIRecipe *MinMaxPhiR,
+                                    VPReductionPHIRecipe *FindIVPhiR,
+                                    VPWidenIntOrFpInductionRecipe *WideIV,
+                                    VPInstruction *MinMaxResult) {
+  Type *Ty = Plan.getVectorLoopRegion()->getCanonicalIVType();
+  // TODO: Support different IV types.
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fhahn wrote:

clarified, thanks

https://github.com/llvm/llvm-project/pull/170223