Implement SystemV struct argument passing

cranelift/codegen/meta/src/cdsl/types.rs

@@ -407,6 +407,8 @@ impl fmt::Debug for VectorType {
 #[derive(Clone, Copy, PartialEq, Eq, Hash)]
 pub(crate) enum SpecialType {
     Flag(shared_types::Flag),
+    // FIXME remove once the old style backends are removed.
+    StructArgument,
 }
 
 impl SpecialType {
@@ -421,6 +423,9 @@ impl SpecialType {
                 "CPU flags representing the result of a floating point comparison. These
                 flags can be tested with a :type:`floatcc` condition code.",
             ),
+            SpecialType::StructArgument => {
+                String::from("After legalization sarg__ arguments will get this type.")
+            }
         }
     }
 
@@ -428,6 +433,7 @@ impl SpecialType {
     pub fn lane_bits(self) -> u64 {
         match self {
             SpecialType::Flag(_) => 0,
+            SpecialType::StructArgument => 0,
         }
     }
 
@@ -436,6 +442,7 @@ impl SpecialType {
         match self {
             SpecialType::Flag(shared_types::Flag::IFlags) => 1,
             SpecialType::Flag(shared_types::Flag::FFlags) => 2,
+            SpecialType::StructArgument => 3,
         }
     }
 }
@@ -445,6 +452,7 @@ impl fmt::Display for SpecialType {
         match *self {
             SpecialType::Flag(shared_types::Flag::IFlags) => write!(f, "iflags"),
             SpecialType::Flag(shared_types::Flag::FFlags) => write!(f, "fflags"),
+            SpecialType::StructArgument => write!(f, "sarg__"),
         }
     }
 }
@@ -456,6 +464,7 @@ impl fmt::Debug for SpecialType {
             "{}",
             match *self {
                 SpecialType::Flag(_) => format!("FlagsType({})", self),
+                SpecialType::StructArgument => format!("StructArgument"),
             }
         )
     }
@@ -469,12 +478,14 @@ impl From<shared_types::Flag> for SpecialType {
 
 pub(crate) struct SpecialTypeIterator {
     flag_iter: shared_types::FlagIterator,
+    done: bool,
 }
 
 impl SpecialTypeIterator {
     fn new() -> Self {
         Self {
             flag_iter: shared_types::FlagIterator::new(),
+            done: false,
         }
     }
 }
@@ -485,7 +496,12 @@ impl Iterator for SpecialTypeIterator {
         if let Some(f) = self.flag_iter.next() {
             Some(SpecialType::from(f))
         } else {
-            None
+            if !self.done {
+                self.done = true;
+                Some(SpecialType::StructArgument)
+            } else {
+                None
+            }
         }
     }
 }