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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@278886 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 7 insertions, 2 deletions

diff --git a/lib/IR/Instruction.cpp b/lib/IR/Instruction.cpp
index ed08f85c60b..cfddbf78f0c 100644
--- a/lib/IR/Instruction.cpp
+++ b/lib/IR/Instruction.cpp
@@ -92,8 +92,13 @@ void Instruction::insertAfter(Instruction *InsertPos) {
 /// 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) {