[llvm] [LV] Fix '-1U' bits for smallest type in getSmallestAndWidestTypes (PR #135783)

[Florian Hahn via llvm-commits]

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@@ -4798,17 +4798,16 @@ LoopVectorizationCostModel::getSmallestAndWidestTypes() {
   // if there are no loads/stores in the loop. In this case, check through the
   // reduction variables to determine the maximum width.
   if (ElementTypesInLoop.empty() && !Legal->getReductionVars().empty()) {
-    // Reset MaxWidth so that we can find the smallest type used by recurrences
-    // in the loop.
-    MaxWidth = -1U;
     for (const auto &PhiDescriptorPair : Legal->getReductionVars()) {
       const RecurrenceDescriptor &RdxDesc = PhiDescriptorPair.second;
       // When finding the min width used by the recurrence we need to account
       // for casts on the input operands of the recurrence.
-      MaxWidth = std::min<unsigned>(
-          MaxWidth, std::min<unsigned>(
+      MinWidth = std::min<unsigned>(
+          MinWidth, std::min<unsigned>(
                         RdxDesc.getMinWidthCastToRecurrenceTypeInBits(),
                         RdxDesc.getRecurrenceType()->getScalarSizeInBits()));
+      MaxWidth = std::max<unsigned>(
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fhahn wrote:

Yes, it seems like the new behavior matches the expectations.

https://github.com/llvm/llvm-project/pull/135783