Add support for MIPS VZ ISA extension

Author: jam1garner

compiler/rustc_codegen_llvm/src/llvm_util.rs

@@ -165,6 +165,10 @@ pub fn time_trace_profiler_finish(file_name: &Path) {
 //
 // To find a list of LLVM's names, check llvm-project/llvm/include/llvm/Support/*TargetParser.def
 // where the * matches the architecture's name
+//
+// For targets not present in the above location, see llvm-project/llvm/lib/Target/{ARCH}/*.td
+// where `{ARCH}` is the architecture name. Look for instances of `SubtargetFeature`.
+//
 // Beware to not use the llvm github project for this, but check the git submodule
 // found in src/llvm-project
 // Though note that Rust can also be build with an external precompiled version of LLVM

compiler/rustc_codegen_ssa/src/target_features.rs

@@ -210,8 +210,11 @@ const POWERPC_ALLOWED_FEATURES: &[(&str, Option<Symbol>)] = &[
     ("vsx", Some(sym::powerpc_target_feature)),
 ];
 
-const MIPS_ALLOWED_FEATURES: &[(&str, Option<Symbol>)] =
-    &[("fp64", Some(sym::mips_target_feature)), ("msa", Some(sym::mips_target_feature))];
+const MIPS_ALLOWED_FEATURES: &[(&str, Option<Symbol>)] = &[
+    ("fp64", Some(sym::mips_target_feature)),
+    ("msa", Some(sym::mips_target_feature)),
+    ("virt", Some(sym::mips_target_feature)),
+];
 
 const RISCV_ALLOWED_FEATURES: &[(&str, Option<Symbol>)] = &[
     ("m", Some(sym::riscv_target_feature)),