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

[Jun Wang via llvm-commits]

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

>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 1/4] [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(

>From b099feec6e743581ec9925002df2a68d8c4b20b5 Mon Sep 17 00:00:00 2001
From: Jun Wang <jwang86 at yahoo.com>
Date: Thu, 27 Aug 2026 15:15:48 -0700
Subject: [PATCH 2/4] Allow +/- to be part of a feature substring, as previous
 Regex does.

---
 llvm/lib/MC/TargetRegistry.cpp | 18 ++++++------------
 1 file changed, 6 insertions(+), 12 deletions(-)

diff --git a/llvm/lib/MC/TargetRegistry.cpp b/llvm/lib/MC/TargetRegistry.cpp
index c8a154b3dcb1f..3bce62b623834 100644
--- a/llvm/lib/MC/TargetRegistry.cpp
+++ b/llvm/lib/MC/TargetRegistry.cpp
@@ -29,19 +29,13 @@ bool Target::isValidFeatureListFormat(StringRef Features) {
   if (Features.empty())
     return true;
 
-  // 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;
-
+  // Each feature starts with '+'/'-' followed by at least one non-comma
+  // character. Features are comma-separated with an optional trailing comma.
   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
+    if (I == 0 || Features[I - 1] == ',') {
+      // At the start of a feature: must have a sign and a non-empty name.
+      if ((Features[I] != '+' && Features[I] != '-') ||
+          I + 1 == Features.size() || Features[I + 1] == ',')
         return false;
     }
   }

>From 0b00b9f83e038ca2304de6fe3d94ef8a3103be45 Mon Sep 17 00:00:00 2001
From: Jun Wang <jwang86 at yahoo.com>
Date: Thu, 27 Aug 2026 15:26:18 -0700
Subject: [PATCH 3/4] Remove the #include directive for Regex.h

---
 llvm/lib/MC/TargetRegistry.cpp | 1 -
 1 file changed, 1 deletion(-)

diff --git a/llvm/lib/MC/TargetRegistry.cpp b/llvm/lib/MC/TargetRegistry.cpp
index 3bce62b623834..ca0621dba4815 100644
--- a/llvm/lib/MC/TargetRegistry.cpp
+++ b/llvm/lib/MC/TargetRegistry.cpp
@@ -16,7 +16,6 @@
 #include "llvm/MC/MCLFI.h"
 #include "llvm/MC/MCObjectStreamer.h"
 #include "llvm/MC/MCObjectWriter.h"
-#include "llvm/Support/Regex.h"
 #include "llvm/Support/raw_ostream.h"
 #include <cassert>
 #include <vector>

>From 71557a8849ba35fdf1723f208ffcf179be90bde9 Mon Sep 17 00:00:00 2001
From: Jun Wang <jwang86 at yahoo.com>
Date: Thu, 27 Aug 2026 15:54:01 -0700
Subject: [PATCH 4/4] Fix for-loop head

---
 llvm/lib/MC/TargetRegistry.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/llvm/lib/MC/TargetRegistry.cpp b/llvm/lib/MC/TargetRegistry.cpp
index ca0621dba4815..185f63637a460 100644
--- a/llvm/lib/MC/TargetRegistry.cpp
+++ b/llvm/lib/MC/TargetRegistry.cpp
@@ -30,7 +30,7 @@ bool Target::isValidFeatureListFormat(StringRef Features) {
 
   // Each feature starts with '+'/'-' followed by at least one non-comma
   // character. Features are comma-separated with an optional trailing comma.
-  for (size_t I = 0; I < Features.size(); ++I) {
+  for (size_t I = 0, E = Features.size(); I != E; ++I) {
     if (I == 0 || Features[I - 1] == ',') {
       // At the start of a feature: must have a sign and a non-empty name.
       if ((Features[I] != '+' && Features[I] != '-') ||