Merge pull request #27424 from gottesmm/swift-5.1-branch-rdar55709778

[simplify-cfg] When determining/searching for the end of a switch_enu…

Author: gottesmm

lib/SILOptimizer/Transforms/SimplifyCFG.cpp

@@ -1878,14 +1878,38 @@ static bool onlyForwardsNone(SILBasicBlock *noneBB, SILBasicBlock *someBB,
 ///    \            ... (more bbs?)
 ///     \           /
 ///       ulimateBB
-static bool hasSameUlitmateSuccessor(SILBasicBlock *noneBB, SILBasicBlock *someBB) {
+static bool hasSameUltimateSuccessor(SILBasicBlock *noneBB, SILBasicBlock *someBB) {
+  // Make sure that both our some, none blocks both have single successors that
+  // are not themselves (which can happen due to single block loops).
   auto *someSuccessorBB = someBB->getSingleSuccessorBlock();
-  if (!someSuccessorBB)
+  if (!someSuccessorBB || someSuccessorBB == someBB)
     return false;
   auto *noneSuccessorBB = noneBB->getSingleSuccessorBlock();
-  while (noneSuccessorBB != nullptr && noneSuccessorBB != someSuccessorBB)
-    noneSuccessorBB = noneSuccessorBB->getSingleSuccessorBlock();
-  return noneSuccessorBB == someSuccessorBB;
+  if (!noneSuccessorBB || noneSuccessorBB == noneBB)
+    return false;
+
+  // If we immediately find a diamond, return true. We are done.
+  if (noneSuccessorBB == someSuccessorBB)
+    return true;
+
+  // Otherwise, lets keep looking down the none case.
+  auto *next = noneSuccessorBB;
+  while (next != someSuccessorBB) {
+    noneSuccessorBB = next;
+    next = noneSuccessorBB->getSingleSuccessorBlock();
+
+    // If we find another single successor and it is not our own block (due to a
+    // self-loop), continue.
+    if (next && next != noneSuccessorBB)
+      continue;
+
+    // Otherwise, we either have multiple successors or a self-loop. We do not
+    // support this, return false.
+    return false;
+  }
+
+  // At this point, we know that next must be someSuccessorBB.
+  return true;
 }
 
 /// Simplify switch_enums on class enums that branch to objc_method calls on
@@ -1920,7 +1944,7 @@ bool SimplifyCFG::simplifySwitchEnumOnObjcClassOptional(SwitchEnumInst *SEI) {
   if (SEI->getCaseDestination(someDecl) != someBB)
     std::swap(someBB, noneBB);
 
-  if (!hasSameUlitmateSuccessor(noneBB, someBB))
+  if (!hasSameUltimateSuccessor(noneBB, someBB))
     return false;
 
   if (!onlyForwardsNone(noneBB, someBB, SEI))

test/SILOptimizer/simplify_switch_enum_objc.sil

@@ -381,3 +381,43 @@ bb8:
 bb9:
   br bb7
 }
+
+sil @infinite_loop_get_optional_nsobject : $@convention(thin) () -> @autoreleased Optional<NSObject>
+sil @infinite_loop_get_superview : $@convention(thin) (NSObject) -> @autoreleased Optional<NSObject>
+
+// Just make sure we do not infinite loop here when looking for successors.
+// CHECK-LABEL: sil @infinite_loop_1 : $@convention(thin) () -> @owned Optional<NSObject> {
+// CHECK: } // end sil function 'infinite_loop_1'
+sil @infinite_loop_1 : $@convention(thin) () -> @owned Optional<NSObject> {
+bb0:
+  %13 = function_ref @infinite_loop_get_optional_nsobject : $@convention(thin) () -> @autoreleased Optional<NSObject>
+  %14 = apply %13() : $@convention(thin) () -> @autoreleased Optional<NSObject>
+  br bb1(%14 : $Optional<NSObject>)
+
+bb1(%16 : $Optional<NSObject>):
+  retain_value %16 : $Optional<NSObject>
+  switch_enum %16 : $Optional<NSObject>, case #Optional.some!enumelt.1: bb2, case #Optional.none!enumelt: bb5
+
+bb2(%19 : $NSObject):
+  release_value %16 : $Optional<NSObject>
+  %21 = enum $Optional<NSObject>, #Optional.none!enumelt
+  release_value %16 : $Optional<NSObject>
+  return %21 : $Optional<NSObject>
+
+bb3:
+  %24 = unchecked_enum_data %16 : $Optional<NSObject>, #Optional.some!enumelt.1
+  strong_retain %24 : $NSObject
+  %26 = function_ref @infinite_loop_get_superview : $@convention(thin) (NSObject) -> @autoreleased Optional<NSObject>
+  %27 = apply %26(%24) : $@convention(thin) (NSObject) -> @autoreleased Optional<NSObject>
+  strong_release %24 : $NSObject
+  release_value %16 : $Optional<NSObject>
+  br bb1(%27 : $Optional<NSObject>)
+
+bb4:
+  release_value %16 : $Optional<NSObject>
+  br bb1(%16 : $Optional<NSObject>)
+
+bb5:
+  release_value %16 : $Optional<NSObject>
+  switch_enum %16 : $Optional<NSObject>, case #Optional.none!enumelt: bb4, default bb3
+}