[mlir] Avoid repeated hash lookups (NFC) (#112158)

Author: kazutakahirata

mlir/lib/Transforms/SROA.cpp

@@ -100,10 +100,11 @@ computeDestructuringInfo(DestructurableMemorySlot &slot,
   mlir::getForwardSlice(slot.ptr, &forwardSlice);
   for (Operation *user : forwardSlice) {
     // If the next operation has no blocking uses, everything is fine.
-    if (!info.userToBlockingUses.contains(user))
+    auto it = info.userToBlockingUses.find(user);
+    if (it == info.userToBlockingUses.end())
       continue;
 
-    SmallPtrSet<OpOperand *, 4> &blockingUses = info.userToBlockingUses[user];
+    SmallPtrSet<OpOperand *, 4> &blockingUses = it->second;
     auto promotable = dyn_cast<PromotableOpInterface>(user);
 
     // An operation that has blocking uses must be promoted. If it is not