Revert "Compute safety information in a much finer granularity."

Use-after-free in llvm::isGuaranteedToExecute.

llvm-svn: 301214

1 files changed, 16 insertions, 8 deletions

diff --git a/llvm/lib/Transforms/Utils/LoopUtils.cpp b/llvm/lib/Transforms/Utils/LoopUtils.cpp
index 062432f..175d013a 100644
--- a/llvm/lib/Transforms/Utils/LoopUtils.cpp
+++ b/llvm/lib/Transforms/Utils/LoopUtils.cpp
@@ -1044,11 +1044,21 @@ bool llvm::isGuaranteedToExecute(const Instruction &Inst,
                                  const DominatorTree *DT, const Loop *CurLoop,
                                  const LoopSafetyInfo *SafetyInfo) {
   // We have to check to make sure that the instruction dominates all
-  // of the exit points.  If it doesn't, then there is a path out of the loop
-  // which does not execute this instruction and its not guaranteed to execute.
-  for (Instruction *ExitInst : SafetyInfo->EarlyExits)
-    if (!DT->dominates(&Inst, ExitInst))
-      return false;
+  // of the exit blocks.  If it doesn't, then there is a path out of the loop
+  // which does not execute this instruction, so we can't hoist it.
+
+  // If the instruction is in the header block for the loop (which is very
+  // common), it is always guaranteed to dominate the exit blocks.  Since this
+  // is a common case, and can save some work, check it now.
+  if (Inst.getParent() == CurLoop->getHeader())
+    // If there's a throw in the header block, we can't guarantee we'll reach
+    // Inst.
+    return !SafetyInfo->HeaderMayThrow;
+
+  // Somewhere in this loop there is an instruction which may throw and make us
+  // exit the loop.
+  if (SafetyInfo->MayThrow)
+    return false;
 
   // Get the exit blocks for the current loop.
   SmallVector<BasicBlock *, 8> ExitBlocks;
@@ -1061,9 +1071,7 @@ bool llvm::isGuaranteedToExecute(const Instruction &Inst,
 
   // As a degenerate case, if the loop is statically infinite then we haven't
   // proven anything since there are no exit blocks.
-  // However, we also special case instruction from the header as the header
-  // is always guaranteed to execute.
-  if (ExitBlocks.empty() && Inst.getParent() != CurLoop->getHeader())
+  if (ExitBlocks.empty())
     return false;
 
   // FIXME: In general, we have to prove that the loop isn't an infinite loop.