Set NumRegisterParameters LLVM module flag to N when -Zregparm=N is set

Author: winstonallo

compiler/rustc_codegen_llvm/src/context.rs

@@ -372,6 +372,15 @@ pub(crate) unsafe fn create_module<'ll>(
         }
     }
 
+    if let Some(regparm_count) = sess.opts.unstable_opts.regparm {
+        llvm::add_module_flag_u32(
+            llmod,
+            llvm::ModuleFlagMergeBehavior::Error,
+            "NumRegisterParameters",
+            regparm_count,
+        );
+    }
+
     if let Some(BranchProtection { bti, pac_ret }) = sess.opts.unstable_opts.branch_protection {
         if sess.target.arch == "aarch64" {
             llvm::add_module_flag_u32(