SILOptimizer: Use getNextDepth()/getMaxDepth()

Author: slavapestov

lib/SILOptimizer/FunctionSignatureTransforms/ExistentialTransform.cpp

@@ -277,10 +277,7 @@ void ExistentialTransform::convertExistentialArgTypesToGenericArgTypes(
   params.append(FTy->getParameters().begin(), FTy->getParameters().end());
 
   /// Determine the existing generic parameter depth.
-  int Depth = 0;
-  if (OrigGenericSig != nullptr) {
-    Depth = OrigGenericSig.getGenericParams().back()->getDepth() + 1;
-  }
+  int Depth = OrigGenericSig.getNextDepth();
 
   /// Index of the Generic Parameter.
   int GPIdx = 0;
@@ -514,10 +511,7 @@ void ExistentialTransform::populateThunkBody() {
     }
   }
 
-  unsigned int OrigDepth = 0;
-  if (F->getLoweredFunctionType()->isPolymorphic()) {
-    OrigDepth = OrigCalleeGenericSig.getGenericParams().back()->getDepth() + 1;
-  }
+  unsigned int OrigDepth = OrigCalleeGenericSig.getNextDepth();
   SubstitutionMap OrigSubMap = F->getForwardingSubstitutionMap();
 
   /// Create substitutions for Apply instructions.

lib/SILOptimizer/Utils/Devirtualize.cpp

@@ -410,7 +410,7 @@ getSubstitutionsForCallee(SILModule &module, CanSILFunctionType baseCalleeType,
   unsigned baseDepth = 0;
   SubstitutionMap baseSubMap;
   if (auto baseClassSig = baseClassDecl->getGenericSignatureOfContext()) {
-    baseDepth = baseClassSig.getGenericParams().back()->getDepth() + 1;
+    baseDepth = baseClassSig.getNextDepth();
 
     // Compute the type of the base class, starting from the
     // derived class type and the type of the method's self
@@ -435,9 +435,7 @@ getSubstitutionsForCallee(SILModule &module, CanSILFunctionType baseCalleeType,
 
   // Add generic parameters from the method itself, ignoring any generic
   // parameters from the derived class.
-  unsigned origDepth = 0;
-  if (auto calleeClassSig = calleeClassDecl->getGenericSignatureOfContext())
-    origDepth = calleeClassSig.getGenericParams().back()->getDepth() + 1;
+  unsigned origDepth = calleeClassDecl->getGenericSignature().getNextDepth();
 
   auto baseCalleeSig = baseCalleeType->getInvocationGenericSignature();
 
@@ -927,10 +925,8 @@ getWitnessMethodSubstitutions(
   // substitutions for the concrete type's generic parameters.
   auto baseSubMap = conformance->getSubstitutionMap();
 
-  unsigned baseDepth = 0;
   auto *rootConformance = conformance->getRootConformance();
-  if (auto conformingTypeSig = rootConformance->getGenericSignature())
-    baseDepth = conformingTypeSig.getGenericParams().back()->getDepth() + 1;
+  unsigned baseDepth = rootConformance->getGenericSignature().getNextDepth();
 
   // witnessThunkSig begins with the optional class 'Self', followed by the
   // generic parameters of the concrete conforming type, followed by the