[llvm] [ConstraintSystem] Build constraint rows in sparse form (NFC). (PR #215735)

[Florian Hahn via llvm-commits]

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@@ -227,25 +217,29 @@ bool ConstraintSystem::mayHaveSolution() {
   return HasSolution;
 }
 
-std::pair<ConstraintSystem, SmallVector<int64_t, 8>>
-ConstraintSystem::getSubSystem(ArrayRef<int64_t> R) const {
+std::pair<ConstraintSystem, ConstraintSystem::RowTy>
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fhahn wrote:

Unfortunately this does not build without `ConstraintSystem::`

https://github.com/llvm/llvm-project/pull/215735