Optimizer: when propagating the concrete type of an existential, make sure to not violate dominance order

Make sure that an enum is only initialized once before it is taken. This implies that the initialization must dominate the take.

Fixes a verifier crash: rdar://139381701

Author: eeckstein

lib/SILOptimizer/Utils/InstOptUtils.cpp

@@ -904,30 +904,34 @@ swift::findInitAddressForTrivialEnum(UncheckedTakeEnumDataAddrInst *utedai) {
   if (!asi)
     return nullptr;
 
-  SILInstruction *singleUser = nullptr;
+  InjectEnumAddrInst *singleInject = nullptr;
+  InitEnumDataAddrInst *singleInit = nullptr;
   for (auto use : asi->getUses()) {
     auto *user = use->getUser();
     if (user == utedai)
       continue;
 
-    // As long as there's only one UncheckedTakeEnumDataAddrInst and one
-    // InitEnumDataAddrInst, we don't care how many InjectEnumAddr and
-    // DeallocStack users there are.
-    if (isa<InjectEnumAddrInst>(user) || isa<DeallocStackInst>(user))
+    // If there is a single init_enum_data_addr and a single inject_enum_addr,
+    // those instructions must dominate the unchecked_take_enum_data_addr.
+    // Otherwise the enum wouldn't be initialized on all control flow paths.
+    if (auto *inj = dyn_cast<InjectEnumAddrInst>(user)) {
+      if (singleInject)
+        return nullptr;
+      singleInject = inj;
       continue;
+    }
 
-    if (singleUser)
-      return nullptr;
+    if (auto *init = dyn_cast<InitEnumDataAddrInst>(user)) {
+      if (singleInit)
+        return nullptr;
+      singleInit = init;
+      continue;
+    }
 
-    singleUser = user;
+    if (isa<DeallocStackInst>(user) || isa<DebugValueInst>(user))
+      continue;
   }
-  if (!singleUser)
-    return nullptr;
-
-  // Assume, without checking, that the returned InitEnumDataAddr dominates the
-  // given UncheckedTakeEnumDataAddrInst, because that's how SIL is defined. I
-  // don't know where this is actually verified.
-  return dyn_cast<InitEnumDataAddrInst>(singleUser);
+  return singleInit;
 }
 
 //===----------------------------------------------------------------------===//

test/SILOptimizer/sil_combine_enums.sil

@@ -16,6 +16,11 @@ enum Numerals {
   case Four
 }
 
+protocol P {
+  mutating func foo()
+}
+
+sil @createit : $@convention(thin) <τ_0_0 where τ_0_0 : P> (@thick τ_0_0.Type) -> @out τ_0_0
 sil @external_func: $@convention(thin) () -> ()
 
 //CHECK-LABEL: eliminate_sw_enum_addr
@@ -663,3 +668,38 @@ bb0(%0 : $S):
   return %11 : $()
 }
 
+// CHECK-LABEL: sil @dont_promote_existential_type_from_non_dominating_block :
+//   Just check that this doesn't crash
+// CHECK:       } // end sil function 'dont_promote_existential_type_from_non_dominating_block'
+sil @dont_promote_existential_type_from_non_dominating_block : $@convention(thin) (@thick any P.Type) -> () {
+bb0(%0 : $@thick any P.Type):
+  %1 = alloc_stack $Optional<any P>
+  cond_br undef, bb1, bb2
+
+bb1:
+  inject_enum_addr %1 : $*Optional<any P>, #Optional.none!enumelt
+  br bb3
+
+bb2:
+  %5 = init_enum_data_addr %1 : $*Optional<any P>, #Optional.some!enumelt
+  %6 = open_existential_metatype %0 : $@thick any P.Type to $@thick (@opened("B0100688-9C78-11EF-8A3C-4EA2A866E4C4", any P) Self).Type
+  %7 = init_existential_addr %5 : $*any P, $@opened("B0100688-9C78-11EF-8A3C-4EA2A866E4C4", any P) Self
+  %f = function_ref @createit : $@convention(thin) <τ_0_0 where τ_0_0 : P> (@thick τ_0_0.Type) -> @out τ_0_0
+  %a = apply %f<@opened("B0100688-9C78-11EF-8A3C-4EA2A866E4C4", any P) Self>(%7, %6) : $@convention(thin) <τ_0_0 where τ_0_0 : P> (@thick τ_0_0.Type) -> @out τ_0_0
+  inject_enum_addr %1 : $*Optional<any P>, #Optional.some!enumelt
+  br bb3
+
+bb3:
+  %9 = unchecked_take_enum_data_addr %1 : $*Optional<any P>, #Optional.some!enumelt
+  dealloc_stack %1 : $*Optional<any P>
+  %11 = alloc_stack [lexical] [var_decl] $any P, var, name "comp"
+  copy_addr [take] %9 to [init] %11 : $*any P
+  %13 = open_existential_addr mutable_access %11 : $*any P to $*@opened("36EE10D8-9C78-11EF-8A3C-4EA2A866E4C4", any P) Self
+  %14 = witness_method $@opened("36EE10D8-9C78-11EF-8A3C-4EA2A866E4C4", any P) Self, #P.foo : <Self where Self : P> (inout Self) -> () -> (), %13 : $*@opened("36EE10D8-9C78-11EF-8A3C-4EA2A866E4C4", any P) Self : $@convention(witness_method: P) <τ_0_0 where τ_0_0 : P> (@inout τ_0_0) -> ()
+  %15 = apply %14<@opened("36EE10D8-9C78-11EF-8A3C-4EA2A866E4C4", any P) Self>(%13) : $@convention(witness_method: P) <τ_0_0 where τ_0_0 : P> (@inout τ_0_0) -> ()
+  destroy_addr %11 : $*any P
+  dealloc_stack %11 : $*any P
+  %18 = tuple ()
+  return %18 : $()
+}
+