[concurrency] Correctly handle dead-end and unreachable blocks in OptimizeHopToExecutor

Fixes an infinite loop.

rdar://problem/71544153

Author: eeckstein

lib/SILOptimizer/Mandatory/OptimizeHopToExecutor.cpp

@@ -144,40 +144,44 @@ void OptimizeHopToExecutor::allocateBlockStates() {
 /// Solve the dataflow in forward direction.
 void OptimizeHopToExecutor::solveDataflowForward() {
   bool changed = false;
+  bool firstRound = true;
   do {
     changed = false;
     for (BlockState &state : blockStates) {
       int newEntry = state.entry;
       for (SILBasicBlock *pred : state.block->getPredecessorBlocks()) {
         newEntry = BlockState::merge(newEntry, block2State[pred]->exit);
       }
-      if (newEntry != state.entry || state.exit == BlockState::NotSet) {
+      if (newEntry != state.entry || firstRound) {
         changed = true;
         state.entry = newEntry;
         if (state.intra == BlockState::NotSet)
           state.exit = state.entry;
       }
     }
+    firstRound = false;
   } while (changed);
 }
 
 /// Solve the dataflow in backward direction.
 void OptimizeHopToExecutor::solveDataflowBackward() {
   bool changed = false;
+  bool firstRound = true;
   do {
     changed = false;
     for (BlockState &state : llvm::reverse(blockStates)) {
       int newExit = state.exit;
       for (SILBasicBlock *succ : state.block->getSuccessorBlocks()) {
         newExit = BlockState::merge(newExit, block2State[succ]->entry);
       }
-      if (newExit != state.exit || state.entry == BlockState::NotSet) {
+      if (newExit != state.exit || firstRound) {
         changed = true;
         state.exit = newExit;
         if (state.intra == BlockState::NotSet)
           state.entry = state.exit;
       }
     }
+    firstRound = false;
   } while (changed);
 }
 
@@ -255,7 +259,7 @@ bool OptimizeHopToExecutor::removeDeadHopToExecutors() {
   // might require a dedicated executor, don't remove a preceeding
   // hop_to_executor instruction.
   for (BlockState &state : blockStates) {
-    state.exit = (state.block->getTerminator()->isFunctionExiting() ?
+    state.exit = (state.block->getSuccessors().empty() ?
                     BlockState::NoExecutorNeeded : BlockState::NotSet);
     state.intra = BlockState::NotSet;
     for (SILInstruction &inst : llvm::reverse(*state.block)) {

test/SILOptimizer/optimize_hop_to_executor.sil

@@ -156,3 +156,53 @@ bb3:
   return %r : $()
 }
 
+// CHECK-LABEL: sil [ossa] @handleUnreachable1 : $@convention(method) @async (@guaranteed MyActor) -> () {
+// CHECK:       bb0(%0 : @guaranteed $MyActor):
+// CHECK-NOT:     hop_to_executor
+// CHECK:       } // end sil function 'handleUnreachable1'
+sil [ossa] @handleUnreachable1 : $@convention(method) @async (@guaranteed MyActor) -> () {
+bb0(%0 : @guaranteed $MyActor):
+  hop_to_executor %0 : $MyActor
+  cond_br undef, bb1, bb2
+bb1:
+  unreachable
+bb2:
+  %r = tuple ()
+  return %r : $()
+}
+
+// CHECK-LABEL: sil [ossa] @handleUnreachable2 : $@convention(method) @async (@guaranteed MyActor) -> () {
+// CHECK:       bb0(%0 : @guaranteed $MyActor):
+// CHECK-NOT:     hop_to_executor
+// CHECK:       } // end sil function 'handleUnreachable2'
+sil [ossa] @handleUnreachable2 : $@convention(method) @async (@guaranteed MyActor) -> () {
+bb0(%0 : @guaranteed $MyActor):
+  cond_br undef, bb1, bb2
+bb1:
+  hop_to_executor %0 : $MyActor
+  unreachable
+bb2:
+  %r = tuple ()
+  return %r : $()
+}
+
+// CHECK-LABEL: sil [ossa] @handleUnreachableBlock : $@convention(method) @async (@guaranteed MyActor) -> () {
+// CHECK:       bb0(%0 : @guaranteed $MyActor):
+// CHECK-NEXT:    hop_to_executor
+// CHECK:       bb2:
+// CHECK-NOT:     hop_to_executor
+// CHECK:       } // end sil function 'handleUnreachableBlock'
+sil [ossa] @handleUnreachableBlock : $@convention(method) @async (@guaranteed MyActor) -> () {
+bb0(%0 : @guaranteed $MyActor):
+  hop_to_executor %0 : $MyActor
+  %f = function_ref @requiredToRunOnActor : $@convention(method) (@guaranteed MyActor) -> ()
+  apply %f(%0) : $@convention(method) (@guaranteed MyActor) -> ()
+  br bb2
+bb1:
+  br bb2
+bb2:
+  hop_to_executor %0 : $MyActor
+  %r = tuple ()
+  return %r : $()
+}
+