[llvm] [AArch64TargetParser]Fix reconstructFromParsedFeatures ignoring negative features (PR #142236)

[Matthias Braun via llvm-commits]

https://github.com/MatzeB created https://github.com/llvm/llvm-project/pull/142236

The `targetFeatureToExtension` function used by
reconstructFromParsedFeatures only found positive `+FEATURE` strings,
but not negative `-FEATURE` strings. Extend the function to handle both
to fix `reconstructFromParsedFeatures`.


>From 92da4def0f7c39a6348669387cfc874ee03f8471 Mon Sep 17 00:00:00 2001
From: Matthias Braun <matze at braunis.de>
Date: Fri, 30 May 2025 16:19:16 -0700
Subject: [PATCH] [AArch64TargetParser]Fix reconstructFromParsedFeatures
 ignoring negative features

The `targetFeatureToExtension` function used by
reconstructFromParsedFeatures only found positive `+FEATURE` strings,
but not negative `-FEATURE` strings. Extend the function to handle both
to fix `reconstructFromParsedFeatures`.
---
 llvm/lib/TargetParser/AArch64TargetParser.cpp    |  5 +++--
 llvm/unittests/TargetParser/TargetParserTest.cpp | 16 ++++++++++++++++
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/llvm/lib/TargetParser/AArch64TargetParser.cpp b/llvm/lib/TargetParser/AArch64TargetParser.cpp
index e13c6e6d28c2b..4a2523440f0f0 100644
--- a/llvm/lib/TargetParser/AArch64TargetParser.cpp
+++ b/llvm/lib/TargetParser/AArch64TargetParser.cpp
@@ -60,7 +60,7 @@ uint64_t AArch64::getFMVPriority(ArrayRef<StringRef> Features) {
   ExtensionSet FeatureBits;
   for (const StringRef Feature : Features) {
     std::optional<FMVInfo> FMV = parseFMVExtension(Feature);
-    if (!FMV) {
+    if (!FMV && Feature.starts_with('+')) {
       if (std::optional<ExtensionInfo> Info = targetFeatureToExtension(Feature))
         FMV = lookupFMVByID(Info->ID);
     }
@@ -181,7 +181,8 @@ std::optional<AArch64::FMVInfo> AArch64::parseFMVExtension(StringRef FMVExt) {
 std::optional<AArch64::ExtensionInfo>
 AArch64::targetFeatureToExtension(StringRef TargetFeature) {
   for (const auto &E : Extensions)
-    if (TargetFeature == E.PosTargetFeature)
+    if (TargetFeature == E.PosTargetFeature ||
+        TargetFeature == E.NegTargetFeature)
       return E;
   return {};
 }
diff --git a/llvm/unittests/TargetParser/TargetParserTest.cpp b/llvm/unittests/TargetParser/TargetParserTest.cpp
index f4c93334ac682..468ef57cb5b9b 100644
--- a/llvm/unittests/TargetParser/TargetParserTest.cpp
+++ b/llvm/unittests/TargetParser/TargetParserTest.cpp
@@ -1831,6 +1831,22 @@ TEST_P(AArch64ExtensionDependenciesBaseCPUTestFixture,
   }
 }
 
+TEST(TargetParserTest, testAArch64ReconstructFromParsedFeatures) {
+  AArch64::ExtensionSet Extensions;
+  std::vector<std::string> FeatureOptions = {
+      "-sve2", "-Baz", "+sve", "+FooBar", "+sve2", "+neon", "-sve",
+  };
+  std::vector<std::string> NonExtensions;
+  Extensions.reconstructFromParsedFeatures(FeatureOptions, NonExtensions);
+
+  std::vector<std::string> NonExtensionsExpected = {"-Baz", "+FooBar"};
+  ASSERT_THAT(NonExtensions, testing::ContainerEq(NonExtensionsExpected));
+  std::vector<StringRef> Features;
+  Extensions.toLLVMFeatureList(Features);
+  std::vector<StringRef> FeaturesExpected = {"+sve2", "+neon", "-sve"};
+  ASSERT_THAT(FeaturesExpected, testing::ContainerEq(FeaturesExpected));
+}
+
 AArch64ExtensionDependenciesBaseArchTestParams
     AArch64ExtensionDependenciesArchData[] = {
         // Base architecture features