From 2082160f33b5b531aa0ffe2f5f8d2e48553da68f Mon Sep 17 00:00:00 2001
From: Philip Reames <listmail@philipreames.com>
Date: Thu, 8 Mar 2018 21:25:30 +0000
Subject: [PATCH] [NFC] Factor out a helper function for checking if a block
 has a potential early implicit exit.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@327065 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/llvm/Analysis/ValueTracking.h   |  7 +++++++
 lib/Analysis/ValueTracking.cpp          |  9 +++++++++
 lib/Transforms/Scalar/JumpThreading.cpp |  4 +---
 lib/Transforms/Utils/LoopUtils.cpp      | 11 ++++-------
 4 files changed, 21 insertions(+), 10 deletions(-)

diff --git a/include/llvm/Analysis/ValueTracking.h b/include/llvm/Analysis/ValueTracking.h
index b326873523c..ced95df94d4 100644
--- a/include/llvm/Analysis/ValueTracking.h
+++ b/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.
   ///
diff --git a/lib/Analysis/ValueTracking.cpp b/lib/Analysis/ValueTracking.cpp
index c132586d874..2ec9cc11493 100644
--- a/lib/Analysis/ValueTracking.cpp
+++ b/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.
diff --git a/lib/Transforms/Scalar/JumpThreading.cpp b/lib/Transforms/Scalar/JumpThreading.cpp
index 8759563267b..15cc709451b 100644
--- a/lib/Transforms/Scalar/JumpThreading.cpp
+++ b/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;
     }
diff --git a/lib/Transforms/Utils/LoopUtils.cpp b/lib/Transforms/Utils/LoopUtils.cpp
index c9c50cd7384..01f3b2dddd3 100644
--- a/lib/Transforms/Utils/LoopUtils.cpp
+++ b/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.
-- 
2.11.0