[llvm] [SandboxVec][Legality] Fix mask on diamond reuse with shuffle (PR #126963)

[Florian Mayer via llvm-commits]

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@@ -202,14 +202,20 @@ CollectDescr
 LegalityAnalysis::getHowToCollectValues(ArrayRef<Value *> Bndl) const {
   SmallVector<CollectDescr::ExtractElementDescr, 4> Vec;
   Vec.reserve(Bndl.size());
-  for (auto [Lane, V] : enumerate(Bndl)) {
+  uint32_t LaneAccum;
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fmayer wrote:

We use this uninitialized in `LaneAccum += VLanes;`

https://github.com/llvm/llvm-project/pull/126963