[specializer] Teach the specializer how to handle indentity {unconditional_checked_cast,checked_cast_br} super_to_archetype.

This is working under the assumption that every class is in a certain
sense its own super class (or we are allowing it to be so for these
casts).

Swift SVN r18020

lib/SILPasses/GenericSpecializer.cpp

@@ -288,16 +288,27 @@ private:
       SILCloner<TypeSubCloner>::visitUnconditionalCheckedCastInst(Inst);
       return;
     case CheckedCastKind::SuperToArchetype: {
-      // Just change the type of cast to an unconditional_checked_cast downcast
-      SILLocation OpLoc = getOpLocation(Inst->getLoc());
       SILValue OpValue = getOpValue(Inst->getOperand());
-      SILType OpType = getOpType(Inst->getType());
+      SILType OpFromTy = OpValue.getType();
+      SILType OpToTy = getOpType(Inst->getType());
+
+      // If the from/to type is the same, just propagate the operand along to
+      // all uses.
+      if (OpFromTy == OpToTy) {
+        auto Pair = std::make_pair(SILValue(Inst),
+                                   OpValue);
+        ValueMap.insert(Pair);
+        return;
+      }
+
+      // Otherwise we assume this is an unconditional_checked_cast downcast.
+      SILLocation OpLoc = getOpLocation(Inst->getLoc());
       CheckedCastKind OpCastKind = CheckedCastKind::Downcast;
       doPostProcess(Inst,
                     getBuilder().createUnconditionalCheckedCast(OpLoc,
                                                                 OpCastKind,
                                                                 OpValue,
-                                                                OpType));
+                                                                OpToTy));
       return;
     }
     case CheckedCastKind::ArchetypeToArchetype:
@@ -422,15 +433,28 @@ private:
       // Just change the type of cast to a checked_cast_br downcast
       SILLocation OpLoc = getOpLocation(Inst->getLoc());
       SILValue OpValue = getOpValue(Inst->getOperand());
-      SILType OpType = getOpType(Inst->getCastType());
+      SILType OpFromTy = OpValue.getType();
+      SILType OpToTy = getOpType(Inst->getCastType());
       SILBasicBlock *OpSuccBB = getOpBasicBlock(Inst->getSuccessBB());
+
+      // If the from/to type is the same, insert a branch to the success basic
+      // block with the relevant argument.
+      if (OpFromTy == OpToTy) {
+        auto Args = ArrayRef<SILValue>(getOpValue(Inst->getOperand()));
+        auto *Br = Builder.createBranch(OpLoc, OpSuccBB, Args);
+        doPostProcess(Inst, Br);
+        return;
+      }
+
+      // Otherwise we assume that we are performing a checked_cast_kind
+      // downcast.
       SILBasicBlock *OpFailBB = getOpBasicBlock(Inst->getFailureBB());
       CheckedCastKind OpCastKind = CheckedCastKind::Downcast;
       doPostProcess(Inst,
                     getBuilder().createCheckedCastBranch(OpLoc,
                                                          OpCastKind,
                                                          OpValue,
-                                                         OpType,
+                                                         OpToTy,
                                                          OpSuccBB,
                                                          OpFailBB));
       return;

test/SILPasses/specialize_checked_cast_branch.swift

@@ -304,6 +304,13 @@ SuperToArchetypeCastC(c: c, t: b)
 // CHECK: bb1
 SuperToArchetypeCastD(d: d, t: c)
 
+// CHECK-LABEL: sil shared @_TTSC30specialize_checked_cast_branch1D___TF30specialize_checked_cast_branch21SuperToArchetypeCastDU__FT1dCS_1D1tQ__Q_ : $@thin (@out D, @owned D, @in D) -> () {
+// CHECK: bb0
+// CHECK: function_ref @_TTSC30specialize_checked_cast_branch1D___TFSs24_injectValueIntoOptionalU__FQ_GSqQ__ : $@thin (@out Optional<D>, @in D) -> ()
+// CHECK-NOT: checked_cast_br super_to_archetype
+// CHECK: bb1
+SuperToArchetypeCastD(d: d, t: d)
+
 //////////////////////////////
 // Existential To Archetype //
 //////////////////////////////

test/SILPasses/specialize_unconditional_checked_cast.swift

@@ -300,6 +300,15 @@ SuperToArchetypeC(c: c, t: b)
 // CHECK-NOT: unconditional_checked_cast super_to_archetype
 SuperToArchetypeD(d: d, t: c)
 
+// CHECK-LABEL: sil shared @_TTSC37specialize_unconditional_checked_cast1D___TF37specialize_unconditional_checked_cast17SuperToArchetypeDU__FT1dCS_1D1tQ__Q_ : $@thin (@out D, @owned D, @in D) -> () {
+// CHECK: bb0
+// CHECK-NEXT: store
+// CHECK-NEXT: load
+// CHECK-NEXT: strong_release
+// CHECK-NEXT: tuple
+// CHECK-NEXT: return
+SuperToArchetypeD(d: d, t: d)
+
 //////////////////////////////
 // Existential To Archetype //
 //////////////////////////////