GCStrategy: Use Twine properly for error message (#132760)

llvm/lib/IR/GCStrategy.cpp

@@ -41,10 +41,9 @@ std::unique_ptr<GCStrategy> llvm::getGCStrategy(const StringRef Name) {
     // be the builtin GCs if nothing else.  The most likely scenario here is
     // that we got here without running the initializers used by the Registry
     // itself and it's registration mechanism.
-    const std::string error =
-        std::string("unsupported GC: ") + Name.str() +
-        " (did you remember to link and initialize the library?)";
-    report_fatal_error(Twine(error));
+    report_fatal_error(
+        "unsupported GC: " + Name +
+        " (did you remember to link and initialize the library?)");
   } else
-    report_fatal_error(Twine(std::string("unsupported GC: ") + Name.str()));
+    report_fatal_error(Twine("unsupported GC: ") + Name);
 }

llvm/test/Transforms/RewriteStatepointsForGC/unsupported-gc-error.ll

@@ -0,0 +1,12 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: not --crash opt -disable-output -passes=rewrite-statepoints-for-gc %s 2>&1 | FileCheck %s
+
+; CHECK: LLVM ERROR: unsupported GC: unsupported-gc
+
+declare void @g()
+declare i32 @h()
+
+define ptr addrspace(1) @f0(ptr addrspace(1) %arg) gc "unsupported-gc" {
+  call void @g() [ "deopt"(i32 100) ]
+  ret ptr addrspace(1) %arg
+}