Inliner: allow the inliner generate partial_apply with an open existential in the substitution list.

There was an old check in the inliner which prevented this, because IRGen didn't support it.
Now it seems that IRGen can handle "partial_apply <@opened...>", so we can remove that check in the inliner.

Author: eeckstein

lib/SILOptimizer/Utils/PerformanceInlinerUtils.cpp

@@ -556,49 +556,6 @@ static bool calleeIsSelfRecursive(SILFunction *Callee) {
   return false;
 }
 
-// Returns true if the callee contains a partial apply instruction,
-// whose substitutions list would contain opened existentials after
-// inlining.
-static bool calleeHasPartialApplyWithOpenedExistentials(FullApplySite AI) {
-  if (!AI.hasSubstitutions())
-    return false;
-
-  SILFunction *Callee = AI.getReferencedFunctionOrNull();
-  assert(Callee && "Trying to optimize a dynamic function?!");
-
-  auto SubsMap = AI.getSubstitutionMap();
-
-  // Bail if there are no open existentials in the list of substitutions.
-  bool HasNoOpenedExistentials = true;
-  for (auto Replacement : SubsMap.getReplacementTypes()) {
-    if (Replacement->hasOpenedExistential()) {
-      HasNoOpenedExistentials = false;
-      break;
-    }
-  }
-
-  if (HasNoOpenedExistentials)
-    return false;
-
-  for (auto &BB : *Callee) {
-    for (auto &I : BB) {
-      if (auto PAI = dyn_cast<PartialApplyInst>(&I)) {
-        if (!PAI->hasSubstitutions())
-          continue;
-
-        // Check if any of substitutions would contain open existentials
-        // after inlining.
-        auto PAISubMap = PAI->getSubstitutionMap();
-        PAISubMap = PAISubMap.subst(SubsMap);
-        if (PAISubMap.hasOpenedExistential())
-          return true;
-      }
-    }
-  }
-
-  return false;
-}
-
 // Returns true if a given apply site should be skipped during the
 // early inlining pass.
 //
@@ -781,12 +738,6 @@ SILFunction *swift::getEligibleFunction(FullApplySite AI,
       return nullptr;
   }
 
-  // IRGen cannot handle partial_applies containing opened_existentials
-  // in its substitutions list.
-  if (calleeHasPartialApplyWithOpenedExistentials(AI)) {
-    return nullptr;
-  }
-
   return Callee;
 }