[llvm] [llvm] Change the implementation of isValidFeatureListFormat (PR #219266)

[Jun Wang via llvm-commits]

https://github.com/jwanggit86 created https://github.com/llvm/llvm-project/pull/219266

This is mostly to change the function-local static variable because some programs are having static initialization order problems. Also the coding standard states statics with ctor/dtor should be avoided. The new implementation also does not use Regex anymore.

>From 00b727d9c24698212181e9ba2e754d1f4446985b Mon Sep 17 00:00:00 2001
From: Jun Wang <jwang86 at yahoo.com>
Date: Thu, 27 Aug 2026 11:44:02 -0700
Subject: [PATCH] [llvm] Change the implementation of isValidFeatureListFormat

This is mostly to change the function-local static variable because
some programs are having static initialization order problems. Also
the coding standard states statics with ctor/dtor should be avoided.
The new implementation also does not use Regex anymore.
---
 llvm/lib/MC/TargetRegistry.cpp | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/llvm/lib/MC/TargetRegistry.cpp b/llvm/lib/MC/TargetRegistry.cpp
index 2727e587496f3..c8a154b3dcb1f 100644
--- a/llvm/lib/MC/TargetRegistry.cpp
+++ b/llvm/lib/MC/TargetRegistry.cpp
@@ -29,8 +29,23 @@ bool Target::isValidFeatureListFormat(StringRef Features) {
   if (Features.empty())
     return true;
 
-  static const llvm::Regex pattern("^([+-][^,]+)(,[+-][^,]+)*,?$");
-  return pattern.match(Features);
+  // Each feature starts with a '+' or '-' and ends with a ',', except
+  // the trailing comma is optional for the last feature.
+  if (Features[0] != '+' && Features[0] != '-')
+    return false;
+
+  for (size_t I = 0; I < Features.size(); ++I) {
+    if (Features[I] == ',') {
+      if (I + 1 == Features.size()) // trailing comma
+        break;
+      if (Features[I + 1] != '+' && Features[I + 1] != '-')
+        return false;
+    } else if (Features[I] == '+' || Features[I] == '-') {
+      if (I + 1 == Features.size() || Features[I + 1] == ',') // empty feature
+        return false;
+    }
+  }
+  return true;
 }
 
 MCStreamer *Target::createMCObjectStreamer(