Pull in r269908 from upstream llvm trunk (by James Molloy):

  [VectorUtils] Fix nasty use-after-free

  In truncateToMinimalBitwidths() we were RAUW'ing an instruction then
  erasing it. However, that intruction could be cached in the map we're
  iterating over. The first check is "I->use_empty()" which in most
  cases would return true, as the (deleted) object was RAUW'd first so
  would have zero use count. However in some cases the object could
  have been polluted or written over and this wouldn't be the case.
  Also it makes valgrind, asan and traditionalists who don't like their
  compiler to crash sad.

  No testcase as there are no externally visible symptoms apart from a
  crash if the stars align.

  Fixes PR26509.

This should fix crashes when building a number of ports on arm64.

Reported by:	andrew

1 files changed, 3 insertions, 1 deletions

diff --git a/contrib/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp b/contrib/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
index 17c25df..2935460 100644
--- a/contrib/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/contrib/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -3161,10 +3161,11 @@ void InnerLoopVectorizer::truncateToMinimalBitwidths() {
   // truncated version of `I` and reextend its result. InstCombine runs
   // later and will remove any ext/trunc pairs.
   //
+  SmallPtrSet<Value *, 4> Erased;
   for (auto &KV : MinBWs) {
     VectorParts &Parts = WidenMap.get(KV.first);
     for (Value *&I : Parts) {
-      if (I->use_empty())
+      if (Erased.count(I) || I->use_empty())
         continue;
       Type *OriginalTy = I->getType();
       Type *ScalarTruncatedTy = IntegerType::get(OriginalTy->getContext(),
@@ -3238,6 +3239,7 @@ void InnerLoopVectorizer::truncateToMinimalBitwidths() {
       Value *Res = B.CreateZExtOrTrunc(NewI, OriginalTy);
       I->replaceAllUsesWith(Res);
       cast<Instruction>(I)->eraseFromParent();
+      Erased.insert(I);
       I = Res;
     }
   }