SILOptimizer: add basic block utilities ReachingReturnBlocks and NonErrorHandlingBlocks

* ReachingReturnBlocks: computes the set of blocks from which a path to the return-block exists (does not include paths to a throw-block)
* NonErrorHandlingBlocks: computes the set of blocks which are not used for error handling, i.e. not (exclusively) reachable from the error-block of a try_apply

Author: eeckstein

include/swift/SILOptimizer/Utils/BasicBlockOptUtils.h

@@ -26,6 +26,7 @@
 #include "swift/SIL/BasicBlockBits.h"
 #include "swift/SIL/SILCloner.h"
 #include "swift/SIL/SILInstruction.h"
+#include "swift/SIL/BasicBlockDatastructures.h"
 #include "swift/SILOptimizer/Utils/InstOptUtils.h"
 
 namespace swift {
@@ -54,6 +55,34 @@ class ReachableBlocks {
   bool isVisited(SILBasicBlock *bb) const { return visited.contains(bb); }
 };
 
+/// Computes the set of blocks from which a path to the return-block exists.
+/// This does not include pathes to a throw-block.
+class ReachingReturnBlocks {
+    BasicBlockWorklist worklist;
+
+public:
+  ReachingReturnBlocks(SILFunction *function);
+
+  /// Returns true if there exists a path from \p block to the return-block.
+  bool reachesReturn(SILBasicBlock *block) const {
+    return worklist.isVisited(block);
+  }
+};
+
+/// Computes the set of blocks which are not used for error handling, i.e. not
+/// (exclusively) reachable from the error-block of a try_apply.
+class NonErrorHandlingBlocks {
+    BasicBlockWorklist worklist;
+
+public:
+  NonErrorHandlingBlocks(SILFunction *function);
+
+  /// Returns true if there exists a path from \p block to the return-block.
+  bool isNonErrorHandling(SILBasicBlock *block) const {
+    return worklist.isVisited(block);
+  }
+};
+
 /// Remove all instructions in the body of \p bb in safe manner by using
 /// undef.
 void clearBlockBody(SILBasicBlock *bb);

lib/SILOptimizer/Utils/BasicBlockOptUtils.cpp

@@ -39,6 +39,33 @@ bool ReachableBlocks::visit(function_ref<bool(SILBasicBlock *)> visitor) {
   return true;
 }
 
+ReachingReturnBlocks::ReachingReturnBlocks(SILFunction *function)
+    : worklist(function) {
+  for (SILBasicBlock &block : *function) {
+    if (isa<ReturnInst>(block.getTerminator()))
+      worklist.push(&block);
+  }
+  
+  while (SILBasicBlock *block = worklist.pop()) {
+    for (SILBasicBlock *pred : block->getPredecessorBlocks()) {
+      worklist.pushIfNotVisited(pred);
+    }
+  }
+}
+
+NonErrorHandlingBlocks::NonErrorHandlingBlocks(SILFunction *function)
+    : worklist(function->getEntryBlock()) {
+  while (SILBasicBlock *block = worklist.pop()) {
+    if (auto ta = dyn_cast<TryApplyInst>(block->getTerminator())) {
+      worklist.pushIfNotVisited(ta->getNormalBB());
+    } else {
+      for (SILBasicBlock *succ : block->getSuccessorBlocks()) {
+        worklist.pushIfNotVisited(succ);
+      }
+    }
+  }
+}
+
 /// Remove all instructions in the body of \p bb in safe manner by using
 /// undef.
 void swift::clearBlockBody(SILBasicBlock *bb) {