[llvm] [LV] Add support for cmp reductions with decreasing IVs. (PR #140451)

[Alexey Bataev via llvm-commits]

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@@ -621,8 +621,16 @@ Value *VPInstruction::generate(VPTransformState &State) {
     unsigned UF = getNumOperands() - 2;
     Value *ReducedPartRdx = State.get(getOperand(2));
     for (unsigned Part = 1; Part < UF; ++Part) {
-      ReducedPartRdx = createMinMaxOp(Builder, RecurKind::SMax, ReducedPartRdx,
-                                      State.get(getOperand(2 + Part)));
+      if (RK == RecurKind::FindLastIV)
+        ReducedPartRdx =
+            createMinMaxOp(Builder, RecurKind::SMax, ReducedPartRdx,
+                           State.get(getOperand(2 + Part)));
+      else
+        ReducedPartRdx =
+            createMinMaxOp(Builder,
+                           RK == RecurKind::FindFirstIVSMin ? RecurKind::SMin
+                                                            : RecurKind::UMin,
+                           ReducedPartRdx, State.get(getOperand(2 + Part)));
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alexey-bataev wrote:

Lots of similar code, better just to preselect RecurKind

https://github.com/llvm/llvm-project/pull/140451