Add ABI annotations to function signatures.

Specify the location of arguments as well as the size of stack argument
array needed. The ABI annotations are optional, just like the value
locations.

Remove the Eq implementation for Signature which was only used by a
single parser test.

docs/langref.rst

@@ -893,6 +893,11 @@ Number of arguments to a function
     incoming frame pointer, and callee-saved registers that are saved in the
     prologue.
 
+Size of function call arguments on the stack
+    At most :math:`2^{32} - 1` bytes.
+
+    This is probably not possible to achieve given the limit on the number of
+    arguments, except by requiring extremely large offsets for stack arguments.
 
 Glossary
 ========

lib/cretonne/src/ir/extfunc.rs

@@ -5,19 +5,30 @@
 //!
 //! This module declares the data types used to represent external functions and call signatures.
 
+use ir::{Type, FunctionName, SigRef, ArgumentLoc};
+use std::cmp;
 use std::fmt::{self, Display, Formatter};
-use ir::{Type, FunctionName, SigRef};
 
 /// Function signature.
 ///
 /// The function signature describes the types of arguments and return values along with other
 /// details that are needed to call a function correctly.
-#[derive(Clone, PartialEq, Eq, Debug)]
+///
+/// A signature can optionally include ISA-specific ABI information which specifies exactly how
+/// arguments and return values are passed.
+#[derive(Clone, Debug)]
 pub struct Signature {
     /// Types of the arguments passed to the function.
     pub argument_types: Vec<ArgumentType>,
     /// Types returned from the function.
     pub return_types: Vec<ArgumentType>,
+
+    /// When the signature has been legalized to a specific ISA, this holds the size of the
+    /// argument array on the stack. Before legalization, this is `None`.
+    ///
+    /// This can be computed from the legalized `argument_types` array as the maximum (offset plus
+    /// byte size) of the `ArgumentLoc::Stack(offset)` argument.
+    pub argument_bytes: Option<u32>,
 }
 
 impl Signature {
@@ -26,8 +37,24 @@ impl Signature {
         Signature {
             argument_types: Vec::new(),
             return_types: Vec::new(),
+            argument_bytes: None,
         }
     }
+
+    /// Compute the size of the stack arguments and mark signature as legalized.
+    ///
+    /// Even if there are no stack arguments, this will set `argument_types` to `Some(0)` instead
+    /// of `None`. This indicates that the signature has been legalized.
+    pub fn compute_argument_bytes(&mut self) {
+        let bytes = self.argument_types
+            .iter()
+            .filter_map(|arg| match arg.location {
+                ArgumentLoc::Stack(offset) => Some(offset + arg.value_type.bits() as u32 / 8),
+                _ => None,
+            })
+            .fold(0, cmp::max);
+        self.argument_bytes = Some(bytes);
+    }
 }
 
 fn write_list(f: &mut Formatter, args: &Vec<ArgumentType>) -> fmt::Result {
@@ -60,7 +87,7 @@ impl Display for Signature {
 ///
 /// This describes the value type being passed to or from a function along with flags that affect
 /// how the argument is passed.
-#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+#[derive(Copy, Clone, Debug)]
 pub struct ArgumentType {
     /// Type of the argument value.
     pub value_type: Type,
@@ -68,6 +95,10 @@ pub struct ArgumentType {
     pub extension: ArgumentExtension,
     /// Place this argument in a register if possible.
     pub inreg: bool,
+
+    /// ABI-specific location of this argument, or `Unassigned` for arguments that have not yet
+    /// been legalized.
+    pub location: ArgumentLoc,
 }
 
 impl ArgumentType {
@@ -77,6 +108,7 @@ impl ArgumentType {
             value_type: vt,
             extension: ArgumentExtension::None,
             inreg: false,
+            location: Default::default(),
         }
     }
 }
@@ -92,7 +124,13 @@ impl Display for ArgumentType {
         if self.inreg {
             write!(f, " inreg")?;
         }
-        Ok(())
+
+        // This really needs a `&TargetAbi` so we can print register units correctly.
+        match self.location {
+            ArgumentLoc::Reg(ru) => write!(f, " [%{}]", ru),
+            ArgumentLoc::Stack(offset) => write!(f, " [{}]", offset),
+            ArgumentLoc::Unassigned => Ok(()),
+        }
     }
 }
 
@@ -154,5 +192,19 @@ mod tests {
         assert_eq!(sig.to_string(), "(i32, i32x4) -> f32");
         sig.return_types.push(ArgumentType::new(B8));
         assert_eq!(sig.to_string(), "(i32, i32x4) -> f32, b8");
+
+        // Test the offset computation algorithm.
+        assert_eq!(sig.argument_bytes, None);
+        sig.argument_types[1].location = ArgumentLoc::Stack(8);
+        sig.compute_argument_bytes();
+        // An `i32x4` at offset 8 requires a 24-byte argument array.
+        assert_eq!(sig.argument_bytes, Some(24));
+        // Order does not matter.
+        sig.argument_types[0].location = ArgumentLoc::Stack(24);
+        sig.compute_argument_bytes();
+        assert_eq!(sig.argument_bytes, Some(28));
+
+        // Writing ABI-annotated signatures.
+        assert_eq!(sig.to_string(), "(i32 [24], i32x4 [8]) -> f32, b8");
     }
 }

lib/reader/src/parser.rs

@@ -1360,7 +1360,7 @@ impl<'a> Parser<'a> {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use cretonne::ir::{ArgumentType, ArgumentExtension};
+    use cretonne::ir::ArgumentExtension;
     use cretonne::ir::types;
     use cretonne::ir::entities::AnyEntity;
     use testfile::{Details, Comment};
@@ -1371,12 +1371,9 @@ mod tests {
     fn argument_type() {
         let mut p = Parser::new("i32 sext");
         let arg = p.parse_argument_type().unwrap();
-        assert_eq!(arg,
-                   ArgumentType {
-                       value_type: types::I32,
-                       extension: ArgumentExtension::Sext,
-                       inreg: false,
-                   });
+        assert_eq!(arg.value_type, types::I32);
+        assert_eq!(arg.extension, ArgumentExtension::Sext);
+        assert_eq!(arg.inreg, false);
         let Error { location, message } = p.parse_argument_type().unwrap_err();
         assert_eq!(location.line_number, 1);
         assert_eq!(message, "expected argument type");