[NFC] Factor out a helper function for checking if a block has a potential early implicit exit.

llvm-svn: 327065

include/llvm/Analysis/ValueTracking.h

@@ -423,6 +423,13 @@ class Value;
   /// though division by zero might cause undefined behavior.
   bool isGuaranteedToTransferExecutionToSuccessor(const Instruction *I);
 
+  /// Returns true if this block does not contain a potential implicit exit.
+  /// This is equivelent to saying that all instructions within the basic block
+  /// are guaranteed to transfer execution to their successor within the basic
+  /// block. This has the same assumptions w.r.t. undefined behavior as the
+  /// instruction variant of this function. 
+  bool isGuaranteedToTransferExecutionToSuccessor(const BasicBlock *BB);
+
   /// Return true if this function can prove that the instruction I
   /// is executed for every iteration of the loop L.
   ///

lib/Analysis/ValueTracking.cpp

@@ -3968,6 +3968,15 @@ bool llvm::isGuaranteedToTransferExecutionToSuccessor(const Instruction *I) {
   return true;
 }
 
+bool llvm::isGuaranteedToTransferExecutionToSuccessor(const BasicBlock *BB) {
+  // TODO: This is slightly consdervative for invoke instruction since exiting
+  // via an exception *is* normal control for them.
+  for (auto I = BB->begin(), E = BB->end(); I != E; ++I)
+    if (!isGuaranteedToTransferExecutionToSuccessor(&*I))
+      return false;
+  return true;
+}
+
 bool llvm::isGuaranteedToExecuteForEveryIteration(const Instruction *I,
                                                   const Loop *L) {
   // The loop header is guaranteed to be executed for every iteration.

lib/Transforms/Scalar/JumpThreading.cpp

@@ -1019,9 +1019,7 @@ bool JumpThreadingPass::ProcessBlock(BasicBlock *BB) {
 
       // Invalidate LVI information for BB if the LVI is not provably true for
       // all of BB.
-      if (any_of(*BB, [](Instruction &I) {
-            return !isGuaranteedToTransferExecutionToSuccessor(&I);
-          }))
+      if (!isGuaranteedToTransferExecutionToSuccessor(BB))
         LVI->eraseBlock(BB);
       return true;
     }

lib/Transforms/Utils/LoopUtils.cpp

@@ -1491,10 +1491,8 @@ void llvm::computeLoopSafetyInfo(LoopSafetyInfo *SafetyInfo, Loop *CurLoop) {
   SafetyInfo->MayThrow = false;
   SafetyInfo->HeaderMayThrow = false;
   // Iterate over header and compute safety info.
-  for (BasicBlock::iterator I = Header->begin(), E = Header->end();
-       (I != E) && !SafetyInfo->HeaderMayThrow; ++I)
-    SafetyInfo->HeaderMayThrow |=
-        !isGuaranteedToTransferExecutionToSuccessor(&*I);
+  SafetyInfo->HeaderMayThrow =
+    !isGuaranteedToTransferExecutionToSuccessor(Header);
 
   SafetyInfo->MayThrow = SafetyInfo->HeaderMayThrow;
   // Iterate over loop instructions and compute safety info.
@@ -1505,9 +1503,8 @@ void llvm::computeLoopSafetyInfo(LoopSafetyInfo *SafetyInfo, Loop *CurLoop) {
   for (Loop::block_iterator BB = std::next(CurLoop->block_begin()),
                             BBE = CurLoop->block_end();
        (BB != BBE) && !SafetyInfo->MayThrow; ++BB)
-    for (BasicBlock::iterator I = (*BB)->begin(), E = (*BB)->end();
-         (I != E) && !SafetyInfo->MayThrow; ++I)
-      SafetyInfo->MayThrow |= !isGuaranteedToTransferExecutionToSuccessor(&*I);
+    SafetyInfo->MayThrow |=
+      !isGuaranteedToTransferExecutionToSuccessor(*BB);
 
   // Compute funclet colors if we might sink/hoist in a function with a funclet
   // personality routine.