[llvm] [NFC][MC][DecoderEmitter] Simplify loop to find the best filter (PR #156237)

[Rahul Joshi via llvm-commits]

https://github.com/jurahul created https://github.com/llvm/llvm-project/pull/156237

Eliminate `AllUseless` as that can be inferred as `BestScore == 0`. Track pointer instead of index for the best filter.

>From 98eabb8b0b7cea41b44358c42adcad6316114843 Mon Sep 17 00:00:00 2001
From: Rahul Joshi <rjoshi at nvidia.com>
Date: Sat, 30 Aug 2025 16:33:48 -0700
Subject: [PATCH] [NFC][MC][DecoderEmitter] Simplify loop to find the best
 filter

---
 llvm/utils/TableGen/DecoderEmitter.cpp | 15 +++++----------
 1 file changed, 5 insertions(+), 10 deletions(-)

diff --git a/llvm/utils/TableGen/DecoderEmitter.cpp b/llvm/utils/TableGen/DecoderEmitter.cpp
index 98569abfbb1a4..871e06a07a7b3 100644
--- a/llvm/utils/TableGen/DecoderEmitter.cpp
+++ b/llvm/utils/TableGen/DecoderEmitter.cpp
@@ -1473,26 +1473,21 @@ FilterChooser::findBestFilter(ArrayRef<bitAttr_t> BitAttrs, bool AllowMixed,
 
   // We have finished with the filter processings.  Now it's time to choose
   // the best performing filter.
-  unsigned BestIndex = 0;
-  bool AllUseless = true;
+  std::unique_ptr<Filter> *BestFilter = nullptr;
   unsigned BestScore = 0;
 
-  for (const auto &[Idx, Filter] : enumerate(Filters)) {
+  for (std::unique_ptr<Filter> &Filter : Filters) {
     unsigned Usefulness = Filter->usefulness();
-
-    if (Usefulness)
-      AllUseless = false;
-
     if (Usefulness > BestScore) {
-      BestIndex = Idx;
+      BestFilter = &Filter;
       BestScore = Usefulness;
     }
   }
 
-  if (AllUseless)
+  if (BestFilter == nullptr)
     return nullptr;
 
-  return std::move(Filters[BestIndex]);
+  return std::move(*BestFilter);
 }
 
 std::unique_ptr<Filter> FilterChooser::findBestFilter() const {