Remove a transformation introduced in PR13652 which fails on the iOS

simulator in a way I can't repro.  Reimplement the important part of it
in a new way to achieve the same effect.

Author: lattner

lib/SILOptimizer/SILCombiner/SILCombiner.h

@@ -242,7 +242,6 @@ class SILCombiner :
   SILInstruction *visitEnumInst(EnumInst *EI);
 
   SILInstruction *visitMarkDependenceInst(MarkDependenceInst *MDI);
-  SILInstruction *visitInitExistentialRefInst(InitExistentialRefInst *IER);
   SILInstruction *visitConvertFunctionInst(ConvertFunctionInst *CFI);
 
   /// Instruction visitor helpers.

lib/SILOptimizer/SILCombiner/SILCombinerMiscVisitors.cpp

@@ -1437,40 +1437,16 @@ SILInstruction *SILCombiner::visitMarkDependenceInst(MarkDependenceInst *MDI) {
       eraseInstFromFunction(*ier);
     return MDI;
   }
-  
-  return nullptr;
-}
 
-
-SILInstruction *SILCombiner::
-visitInitExistentialRefInst(InitExistentialRefInst *IER) {
-  // Arrays in particular end up with chains of init/open existential refs,
-  // which convert back and forth between a class reference and an existential
-  // reference e.g. like this:
-  //
-  // %a = init_existential_ref %x : $_ContiguousArrayStorageBase :
-  //                                $_ContiguousArrayStorageBase, $_NSArrayCore
-  // %b = open_existential_ref %a : $_NSArrayCore to
-  //                                $@opened("EA85...") _NSArrayCore
-  //
-  // %c = init_existential_ref %b : $@opened("EA85...") _NSArrayCore :
-  //                                $@opened("EA85...") _NSArrayCore, $AnyObject
-  // we can simplify this by having %c initialize itself from the %x reference
-  // directly.
-  if (auto *ORE = dyn_cast<OpenExistentialRefInst>(IER->getOperand())) {
-    if (auto *IER2 = dyn_cast<InitExistentialRefInst>(ORE->getOperand())) {
-      
-      // We create a new instruction, instead of modifying the existing one
-      // in place, because we need the result type of "%c" but the operand list
-      // of "%a", and the number of dependent types could disagree.
-      return Builder.createInitExistentialRef(IER->getLoc(), IER->getType(),
-                                              IER->getFormalConcreteType(),
-                                              IER2->getOperand(),
-                                              IER->getConformances());
-      
-    }
+  // Conversions from a class to AnyObject also happen a lot, we can just depend
+  // on the class reference.
+  if (auto oeri = dyn_cast<OpenExistentialRefInst>(MDI->getBase())) {
+    MDI->setBase(oeri->getOperand());
+    if (oeri->use_empty())
+      eraseInstFromFunction(*oeri);
+    return MDI;
   }
-  
+
   return nullptr;
 }
 

test/SILOptimizer/sil_combine.sil

@@ -2083,19 +2083,6 @@ bb0(%0 : $B, %1 : $@sil_unowned B, %2 : $AnyObject, %3: $@sil_unmanaged AnyObjec
   return %9999 : $(B, @sil_unowned B, AnyObject, @sil_unmanaged AnyObject)
 }
 
-// CHECK-LABEL: sil @collapse_init_open_init_ref_cast
-// CHECK:       bb0([[Ref:%.*]]: $MyClass):
-// CHECK-NEXT:     init_existential_ref
-// CHECK-NEXT:     return
-sil @collapse_init_open_init_ref_cast : $@convention(thin) (MyClass) -> (AnyObject) {
-bb0(%0: $MyClass):
-  %1 = init_existential_ref %0 : $MyClass : $MyClass, $AnyObject
-  %2 = open_existential_ref %1 : $AnyObject to $@opened("2CAE06CE-5F10-11E4-AF13-C82A1428F987") AnyObject
-  %3 = init_existential_ref %2 : $@opened("2CAE06CE-5F10-11E4-AF13-C82A1428F987") AnyObject : $@opened("2CAE06CE-5F10-11E4-AF13-C82A1428F987") AnyObject, $AnyObject
-  return %3 : $AnyObject
-}
-
-
 // CHECK-LABEL: sil @collapse_existential_pack_unpack_unchecked_ref_cast
 // CHECK:       bb0([[Ref:%.*]]: $MyClass):
 // CHECK-NOT:     init_existential_ref
@@ -3459,5 +3446,22 @@ bb0(%0 : $*Builtin.Int64, %1 : $B):
   return %4 : $Builtin.Int64
 }
 
+// CHECK-LABEL: sil @mark_dependence_base2
+// CHECK: bb0(
+// CHECK-NOT: open_existential_ref
+// CHECK-NOT: enum
+// CHECK-NEXT: mark_dependence
+// CHECK-NEXT: load
+// CHECK: return
+sil @mark_dependence_base2 : $@convention(thin) (@inout Builtin.Int64, @owned B) -> Builtin.Int64 {
+bb0(%0 : $*Builtin.Int64, %1 : $B):
+  %2 = init_existential_ref %1 : $B : $B, $AnyObject
+  %3 = open_existential_ref %2 : $AnyObject to $@opened("B674783A-EF08-11E7-97D6-8C85900CB088") _NSArrayCore
+  %5 = mark_dependence %0 : $*Builtin.Int64 on %3 : $@opened("B674783A-EF08-11E7-97D6-8C85900CB088") _NSArrayCore
+
+  %4 = load %5 : $*Builtin.Int64
+  return %4 : $Builtin.Int64
+}
+