Revert r340921 "[NFC] Unify guards detection"

This broke the build, see e.g.

http://lab.llvm.org:8011/builders/clang-cmake-armv8-lnt/builds/4626/
http://lab.llvm.org:8011/builders/clang-ppc64be-linux-lnt/builds/18647/
http://lab.llvm.org:8011/builders/clang-cmake-x86_64-avx2-linux/builds/5856/
http://lab.llvm.org:8011/builders/lld-x86_64-freebsd/builds/22800/

> We have multiple places in code where we try to identify whether or not
> some instruction is a guard. This patch factors out this logic into a separate
> utility function which works uniformly in all places.
>
> Differential Revision: https://reviews.llvm.org/D51152
> Reviewed By: fedor.sergeev

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@340923 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Analysis/AliasSetTracker.cpp

@@ -34,7 +34,6 @@
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/raw_ostream.h"
-#include "llvm/Transforms/Utils/GuardUtils.h"
 #include <cassert>
 #include <cstdint>
 #include <vector>
@@ -173,7 +172,8 @@ void AliasSet::addUnknownInst(Instruction *I, AliasAnalysis &AA) {
   // Guards are marked as modifying memory for control flow modelling purposes,
   // but don't actually modify any specific memory location.
   using namespace PatternMatch;
-  bool MayWriteMemory = I->mayWriteToMemory() && !isGuard(I) &&
+  bool MayWriteMemory = I->mayWriteToMemory() &&
+    !match(I, m_Intrinsic<Intrinsic::experimental_guard>()) &&
     !(I->use_empty() && match(I, m_Intrinsic<Intrinsic::invariant_start>()));
   if (!MayWriteMemory) {
     Alias = SetMayAlias;