[llvm] [VPlan] Support multiple F(Max|Min)Num reductions. (PR #161735)

[Mel Chen via llvm-commits]

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@@ -884,52 +871,69 @@ bool VPlanTransforms::handleMaxMinNumReductions(VPlan &Plan) {
   }
 
   VPBasicBlock *LatchVPBB = LoopRegion->getExitingBasicBlock();
+  VPBasicBlock *MiddleVPBB = Plan.getMiddleBlock();
+  VPBuilder MiddleBuilder(MiddleVPBB, MiddleVPBB->begin());
   VPBuilder Builder(LatchVPBB->getTerminator());
-  auto *LatchExitingBranch = cast<VPInstruction>(LatchVPBB->getTerminator());
-  assert(LatchExitingBranch->getOpcode() == VPInstruction::BranchOnCount &&
+  VPValue *AnyNaN = nullptr;
+  SmallPtrSet<VPValue *, 2> RdxResults;
+  for (VPReductionPHIRecipe *RedPhiR : ReductionsToConvert) {
+    VPValue *MinMaxOp = GetMinMaxCompareValue(RedPhiR);
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Mel-Chen wrote:

Is the recurrence chain for RecurKind::FMinNum and RecurKind::FMaxNum limited to a single min/max operation (similar to FindLast, which has only one select)?
Seems like GetMinMaxCompareValue only returns the last min/max operation.
If multiple min/max operations can appear in the recurrence chain, should all of them be handled? Or only handle the last one is correct?

https://github.com/llvm/llvm-project/pull/161735