[llvm] r278886 - Scalar: Avoid dereferencing end() in IndVarSimplify

[Duncan P. N. Exon Smith via llvm-commits]

Author: dexonsmith
Date: Tue Aug 16 20:54:41 2016
New Revision: 278886

URL: http://llvm.org/viewvc/llvm-project?rev=278886&view=rev
Log:
Scalar: Avoid dereferencing end() in IndVarSimplify

IndVarSimplify::sinkUnusedInvariants calls
BasicBlock::getFirstInsertionPt on the ExitBlock and moves instructions
before it.  This can return end(), so it's not safe to dereference.  Add
an iterator-based overload to Instruction::moveBefore to avoid the UB.

Modified:
    llvm/trunk/include/llvm/IR/Instruction.h
    llvm/trunk/lib/IR/Instruction.cpp
    llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp

Modified: llvm/trunk/include/llvm/IR/Instruction.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/IR/Instruction.h?rev=278886&r1=278885&r2=278886&view=diff
==============================================================================
--- llvm/trunk/include/llvm/IR/Instruction.h (original)
+++ llvm/trunk/include/llvm/IR/Instruction.h Tue Aug 16 20:54:41 2016
@@ -94,6 +94,11 @@ public:
   /// the basic block that MovePos lives in, right before MovePos.
   void moveBefore(Instruction *MovePos);
 
+  /// Unlink this instruction and insert into BB before I.
+  ///
+  /// \pre I is a valid iterator into BB.
+  void moveBefore(BasicBlock &BB, SymbolTableList<Instruction>::iterator I);
+
   //===--------------------------------------------------------------------===//
   // Subclass classification.
   //===--------------------------------------------------------------------===//

Modified: llvm/trunk/lib/IR/Instruction.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/IR/Instruction.cpp?rev=278886&r1=278885&r2=278886&view=diff
==============================================================================
--- llvm/trunk/lib/IR/Instruction.cpp (original)
+++ llvm/trunk/lib/IR/Instruction.cpp Tue Aug 16 20:54:41 2016
@@ -92,8 +92,13 @@ void Instruction::insertAfter(Instructio
 /// Unlink this instruction from its current basic block and insert it into the
 /// basic block that MovePos lives in, right before MovePos.
 void Instruction::moveBefore(Instruction *MovePos) {
-  MovePos->getParent()->getInstList().splice(
-      MovePos->getIterator(), getParent()->getInstList(), getIterator());
+  moveBefore(*MovePos->getParent(), MovePos->getIterator());
+}
+
+void Instruction::moveBefore(BasicBlock &BB,
+                             SymbolTableList<Instruction>::iterator I) {
+  assert(I == BB.end() || I->getParent() == &BB);
+  BB.getInstList().splice(I, getParent()->getInstList(), getIterator());
 }
 
 void Instruction::setHasNoUnsignedWrap(bool b) {

Modified: llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp?rev=278886&r1=278885&r2=278886&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp Tue Aug 16 20:54:41 2016
@@ -2058,7 +2058,7 @@ void IndVarSimplify::sinkUnusedInvariant
   BasicBlock *Preheader = L->getLoopPreheader();
   if (!Preheader) return;
 
-  Instruction *InsertPt = &*ExitBlock->getFirstInsertionPt();
+  BasicBlock::iterator InsertPt = ExitBlock->getFirstInsertionPt();
   BasicBlock::iterator I(Preheader->getTerminator());
   while (I != Preheader->begin()) {
     --I;
@@ -2127,9 +2127,9 @@ void IndVarSimplify::sinkUnusedInvariant
       Done = true;
     }
 
-    ToMove->moveBefore(InsertPt);
+    ToMove->moveBefore(*ExitBlock, InsertPt);
     if (Done) break;
-    InsertPt = ToMove;
+    InsertPt = ToMove->getIterator();
   }
 }