From 7e22a612808105a90ca5f66b0270a6aedff06af2 Mon Sep 17 00:00:00 2001
From: Stefan Weigl-Bosker <stefan@s00.xyz>
Date: Fri, 19 Dec 2025 18:17:38 -0500
Subject: [PATCH] [MC] Handle malformed `target-feature`

---
 llvm/lib/MC/MCSubtargetInfo.cpp                     | 8 +++++---
 llvm/test/CodeGen/Generic/invalid-target-feature.ll | 9 +++++++++
 2 files changed, 14 insertions(+), 3 deletions(-)
 create mode 100644 llvm/test/CodeGen/Generic/invalid-target-feature.ll

diff --git a/llvm/lib/MC/MCSubtargetInfo.cpp b/llvm/lib/MC/MCSubtargetInfo.cpp
index 89a08327dd259..242712a61f197 100644
--- a/llvm/lib/MC/MCSubtargetInfo.cpp
+++ b/llvm/lib/MC/MCSubtargetInfo.cpp
@@ -59,9 +59,11 @@ void ClearImpliedBits(FeatureBitset &Bits, unsigned Value,
 
 static void ApplyFeatureFlag(FeatureBitset &Bits, StringRef Feature,
                              ArrayRef<SubtargetFeatureKV> FeatureTable) {
-  assert(SubtargetFeatures::hasFlag(Feature) &&
-         "Feature flags should start with '+' or '-'");
-
+  if (!SubtargetFeatures::hasFlag(Feature)) {
+    errs() << "Feature flag '" << Feature
+           << "' must start with either '+' or '-' (ignoring feature)\n";
+    return;
+  }
   // Find feature in table.
   const SubtargetFeatureKV *FeatureEntry =
       Find(SubtargetFeatures::StripFlag(Feature), FeatureTable);
diff --git a/llvm/test/CodeGen/Generic/invalid-target-feature.ll b/llvm/test/CodeGen/Generic/invalid-target-feature.ll
new file mode 100644
index 0000000000000..43e16291576bd
--- /dev/null
+++ b/llvm/test/CodeGen/Generic/invalid-target-feature.ll
@@ -0,0 +1,9 @@
+; Check that we handle a malformed feature flag gracefully.
+
+; RUN: llc %s -o - 2>&1 | FileCheck %s
+
+; CHECK: Feature flag 'foobar' must start with either '+' or '-' (ignoring feature)
+define void @f() "target-features"="foobar" {
+entry:
+  ret void
+}