[LoopUtils] Freeze compare results for diff checks instead of pointers.

THe freezes are introduced to avoid branch on undef/poison, if any of
the pointers may be poison. The same can be achieved by just freezing
the compare, which reduces the number of freezes needed. See
https://alive2.llvm.org/ce/z/NHa_ud

Note that the individual compares need to be frozen and it is not
sufficient to only freeze the resulting OR:

Result OR frozen only (UNSOUND): https://alive2.llvm.org/ce/z/YzFHQY
Individual conds frozen (SOUND): https://alive2.llvm.org/ce/z/5L6Z3f

1 files changed, 3 insertions, 6 deletions

diff --git a/llvm/lib/Transforms/Utils/LoopUtils.cpp b/llvm/lib/Transforms/Utils/LoopUtils.cpp
index c03d118..8bb4e17 100644
--- a/llvm/lib/Transforms/Utils/LoopUtils.cpp
+++ b/llvm/lib/Transforms/Utils/LoopUtils.cpp
@@ -1795,15 +1795,12 @@ Value *llvm::addDiffRuntimeChecks(
                              ConstantInt::get(Ty, IC * C.AccessSize));
     Value *Sink = Expander.expandCodeFor(C.SinkStart, Ty, Loc);
     Value *Src = Expander.expandCodeFor(C.SrcStart, Ty, Loc);
-    if (C.NeedsFreeze) {
-      IRBuilder<> Builder(Loc);
-      Sink = Builder.CreateFreeze(Sink, Sink->getName() + ".fr");
-      Src = Builder.CreateFreeze(Src, Src->getName() + ".fr");
-    }
     Value *Diff = ChkBuilder.CreateSub(Sink, Src);
     Value *IsConflict =
         ChkBuilder.CreateICmpULT(Diff, VFTimesUFTimesSize, "diff.check");
-
+    if (C.NeedsFreeze)
+      IsConflict =
+          ChkBuilder.CreateFreeze(IsConflict, IsConflict->getName() + ".fr");
     if (MemoryRuntimeCheck) {
       IsConflict =
           ChkBuilder.CreateOr(MemoryRuntimeCheck, IsConflict, "conflict.rdx");