From 1b50778271f4537514fcb02c0a12e36262d71070 Mon Sep 17 00:00:00 2001
From: Cassie Jones <code@witchoflight.com>
Date: Sun, 1 Mar 2020 21:15:16 +0100
Subject: [PATCH] Implement variable capture

We just copy the variables into the closure environment after it gets
allocated. This involves a decent chunk of stack traffic because we have
to increment their reference counts.

In the process, I figured out that the "ivy_app_mut" optimization for
later functions isn't sound in the presence of nested functions, because
one of the earlier applications can return a shared function which isn't
acceptable to mutate. (There are ways to make it sound if you know for
sure what functions are being called).
---
 ivy-examples/break.vy                       |  5 +++++
 ivy-examples/minimal-captures.vy            |  1 +
 program.vy => ivy-examples/program.vy       |  0
 sixty-four.vy => ivy-examples/sixty-four.vy |  6 +++---
 src/trans/x64.rs                            | 23 +++++++++++++--------
 5 files changed, 23 insertions(+), 12 deletions(-)
 create mode 100644 ivy-examples/break.vy
 create mode 100644 ivy-examples/minimal-captures.vy
 rename program.vy => ivy-examples/program.vy (100%)
 rename sixty-four.vy => ivy-examples/sixty-four.vy (50%)

diff --git a/ivy-examples/break.vy b/ivy-examples/break.vy
new file mode 100644
index 0000000..0353a36
--- /dev/null
+++ b/ivy-examples/break.vy
@@ -0,0 +1,5 @@
+(let (
+    [base (lam (y) (debug y))]
+    [f (lam (x) base)]
+    [use (f 0 0)]
+) (f use use))
diff --git a/ivy-examples/minimal-captures.vy b/ivy-examples/minimal-captures.vy
new file mode 100644
index 0000000..f34202b
--- /dev/null
+++ b/ivy-examples/minimal-captures.vy
@@ -0,0 +1 @@
+((lam (x) (lam (y) (x y))) debug 0)
diff --git a/program.vy b/ivy-examples/program.vy
similarity index 100%
rename from program.vy
rename to ivy-examples/program.vy
diff --git a/sixty-four.vy b/ivy-examples/sixty-four.vy
similarity index 50%
rename from sixty-four.vy
rename to ivy-examples/sixty-four.vy
index d17d061..78e88eb 100644
--- a/sixty-four.vy
+++ b/ivy-examples/sixty-four.vy
@@ -1,8 +1,8 @@
 (let (
     [zero (lam (f x) x)]
-    [succ (lam (n f x) (f (n f x)))]
-    [add (lam (m n f x) (m f (n f x)))]
-    [mul (lam (m n f x) (m (n f) x))]
+    [succ (lam (n) (lam (f x) (f (n f x))))]
+    [add (lam (m n) (lam (f x) (m f (n f x))))]
+    [mul (lam (m n) (lam (f x) (m (n f) x)))]
     [two (succ (succ zero))]
     [four (add two two)]
     [_64 (mul (mul four four) four)]
diff --git a/src/trans/x64.rs b/src/trans/x64.rs
index 6d3c921..3a07c77 100644
--- a/src/trans/x64.rs
+++ b/src/trans/x64.rs
@@ -207,11 +207,9 @@ fn compile_func(func: &Func) -> Definition {
         Var::Upvar(x) => upvar(x),
         Var::Ssa(s) => stack(&s),
     };
-    let load = |s| {
-        match func.block[s] {
-            Code::Load(v) => address(v),
-            _ => stack(s),
-        }
+    let load = |s| match func.block[s] {
+        Code::Load(v) => address(v),
+        _ => stack(s),
     };
     for ssa in &func.order {
         match &func.block[ssa] {
@@ -230,9 +228,16 @@ fn compile_func(func: &Func) -> Definition {
                 body.push(Inst::Imm(Reg::Rsi, *params as i64));
                 body.push(Inst::Imm(Reg::Rdx, upvars.len() as i64));
                 body.push(Inst::Call(extern_label!("ivy_make_lam")));
-                // @TODO: Implement copying in closure captures
-                assert!(upvars.is_empty());
                 body.push(Inst::Store(stack(ssa), Reg::Rax));
+                for (i, s) in upvars.iter().enumerate() {
+                    body.push(Inst::Load(Reg::Rdi, load(s)));
+                    body.push(Inst::Store(
+                        Addr::Off(Reg::Rax, HEADER_SIZE + (*params as i32) * 8 + i as i32 * 8),
+                        Reg::Rdi,
+                    ));
+                    body.push(Inst::Call(extern_label!("ivy_incref")));
+                    body.push(Inst::Load(Reg::Rax, stack(ssa)));
+                }
             }
             Code::App(terms) => {
                 let mut terms = terms.iter();
@@ -248,7 +253,7 @@ fn compile_func(func: &Func) -> Definition {
                 while let Some(term) = terms.next() {
                     body.push(Inst::Mov(Reg::Rdi, Reg::Rax));
                     body.push(Inst::Load(Reg::Rsi, load(term)));
-                    body.push(Inst::Call(extern_label!("ivy_app_mut")));
+                    body.push(Inst::Call(extern_label!("ivy_app")));
                 }
                 body.push(Inst::Store(stack(ssa), Reg::Rax));
             }
@@ -330,7 +335,7 @@ impl fmt::Display for Addr {
     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
         match self {
             Addr::Rip(l) => write!(fmt, "[rip + {}]", l),
-            Addr::Off(r, o) => write!(fmt, "[{} + {}]", r, o),
+            Addr::Off(r, o) => write!(fmt, "[{} + 0x{:02x}]", r, o),
         }
     }
 }
-- 
2.43.2