Fix condition forwarding for switch_enum with default in ossa

In ossa, switch_enum's destination accepts an argument. Fixup
condition forwarding to correctly forward the enum in this case.

Fixes rdar://143042093

Author: meg-gupta

lib/SILOptimizer/Transforms/ConditionForwarding.cpp

@@ -290,9 +290,13 @@ bool ConditionForwarding::tryOptimize(SwitchEnumInst *SEI) {
     llvm::SmallVector<SILValue, 2> BranchArgs;
     unsigned HasEnumArg = NeedEnumArg.contains(SEDest);
     if (SEDest->getNumArguments() == 1 + HasEnumArg) {
-      // The successor block has an original argument, which is the Enum's
-      // payload.
-      BranchArgs.push_back(EI->getOperand());
+      if (SEI->hasDefault() && SEDest == SEI->getDefaultBB()) {
+        BranchArgs.push_back(EI);
+      } else {
+        // The successor block has an original argument, which is the Enum's
+        // payload.
+        BranchArgs.push_back(EI->getOperand());
+      }
     }
     if (HasEnumArg) {
       // The successor block has a new argument (which we created above) where

test/SILOptimizer/conditionforwarding_nontrivial_ossa.sil

@@ -21,6 +21,13 @@ enum FakeOptional<T> {
   case some(T)
 }
 
+enum PrimaryColor : Int {
+  case red = 0
+  case blue = 1
+  case green = 2
+}
+
+sil [ossa] @use_color : $@convention(thin) (PrimaryColor) -> ()
 sil [ossa] @callee : $@convention(thin) () -> ()
 sil [ossa] @use_enum : $@convention(thin) (@guaranteed E) -> ()
 sil [ossa] @use_int : $@convention(thin) (Builtin.Int64) -> ()
@@ -134,6 +141,34 @@ bb6:
   return %r : $()
 }
 
+sil [ossa] @simple_forwarding4 : $@convention(thin) (Builtin.Int1) -> () {
+bb0(%0 : $Builtin.Int1):
+  cond_br %0, bb1, bb2
+
+bb1:
+  %2 = enum $PrimaryColor, #PrimaryColor.red!enumelt
+  br bb3(%2 : $PrimaryColor)
+
+bb2:
+  %3 = enum $PrimaryColor, #PrimaryColor.blue!enumelt
+  br bb3(%3 : $PrimaryColor)
+
+bb3(%14 : $PrimaryColor):
+  switch_enum %14 : $PrimaryColor, case #PrimaryColor.red!enumelt: bb4, default bb5
+
+bb4:
+  br bb6
+
+bb5(%18 : $PrimaryColor):
+  %15 = function_ref @use_color : $@convention(thin) (PrimaryColor) -> ()
+  %16 = apply %15(%18) : $@convention(thin) (PrimaryColor) -> ()
+  br bb6
+
+bb6:
+  %r = tuple ()
+  return %r : $()
+}
+
 // CHECK-LABEL: sil [ossa] @simple_switch_enum_forwarding1 : 
 // CHECK: bb0({{.*}}):
 // CHECK-NEXT: br bb3