[vm/compiler] Fix liveness analysis for unboxed parameters on 32-bit.

Fixes dart-lang/sdk#41977

Cq-Include-Trybots: luci.dart.try:vm-kernel-precomp-linux-release-simarm-try,vm-kernel-precomp-linux-debug-simarm_x64-try
Change-Id: Ifcba1aac8e23aa382bdafe7506ce1725b8f2221d
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/148602
Reviewed-by: Vyacheslav Egorov <[email protected]>
Commit-Queue: Vyacheslav Egorov <[email protected]>

Author: linzj

runtime/vm/compiler/backend/linearscan.cc

@@ -276,6 +276,10 @@ void SSALivenessAnalysis::ComputeInitialSets() {
         const intptr_t vreg = def->ssa_temp_index();
         kill_[entry->postorder_number()]->Add(vreg);
         live_in_[entry->postorder_number()]->Remove(vreg);
+        if (def->HasPairRepresentation()) {
+          kill_[entry->postorder_number()]->Add(ToSecondPairVreg((vreg)));
+          live_in_[entry->postorder_number()]->Remove(ToSecondPairVreg(vreg));
+        }
       }
     }
   }