1 files changed, 22 insertions, 0 deletions
diff --git a/compiler/rustc_target/src/spec/abi.rs b/compiler/rustc_target/src/spec/abi.rs
index ce45fa13970..cb2a0c04c6a 100644
--- a/compiler/rustc_target/src/spec/abi.rs
+++ b/compiler/rustc_target/src/spec/abi.rs
@@ -40,6 +40,28 @@ pub enum Abi {
     RustCold,
 }
 
+impl Abi {
+    pub fn supports_varargs(self) -> bool {
+        // * C and Cdecl obviously support varargs.
+        // * C can be based on SysV64 or Win64, so they must support varargs.
+        // * EfiApi is based on Win64 or C, so it also supports it.
+        //
+        // * Stdcall does not, because it would be impossible for the callee to clean
+        //   up the arguments. (callee doesn't know how many arguments are there)
+        // * Same for Fastcall, Vectorcall and Thiscall.
+        // * System can become Stdcall, so is also a no-no.
+        // * Other calling conventions are related to hardware or the compiler itself.
+        match self {
+            Self::C { .. }
+            | Self::Cdecl { .. }
+            | Self::Win64 { .. }
+            | Self::SysV64 { .. }
+            | Self::EfiApi => true,
+            _ => false,
+        }
+    }
+}
+
 #[derive(Copy, Clone)]
 pub struct AbiData {
     abi: Abi,