From bcf23d569984ade33d202ddcc435b502dc012cd0 Mon Sep 17 00:00:00 2001
From: Folkert <folkert@folkertdev.nl>
Date: Wed, 14 Jul 2021 00:30:00 +0200
Subject: [PATCH] Revert "improvements to reset reuse"

This reverts commit e0ce2892add81771e5585c52389499191c9dba08.
---
 compiler/mono/src/reset_reuse.rs | 50 ++++++++++++++++----------------
 1 file changed, 25 insertions(+), 25 deletions(-)

diff --git a/compiler/mono/src/reset_reuse.rs b/compiler/mono/src/reset_reuse.rs
index bb5d73c168..a19b32113a 100644
--- a/compiler/mono/src/reset_reuse.rs
+++ b/compiler/mono/src/reset_reuse.rs
@@ -114,21 +114,23 @@ fn function_s<'a, 'i>(
             let body: &Stmt = *body;
             let new_body = function_s(env, w, c, body);
 
-            let new_join = if body == new_body {
-                let new_remainder = function_s(env, w, c, remainder);
-                Join {
-                    id,
-                    parameters,
-                    body,
-                    remainder: new_remainder,
-                }
-            } else {
+            let new_join = if std::ptr::eq(body, new_body) || body == new_body {
+                // the join point body will consume w
                 Join {
                     id,
                     parameters,
                     body: new_body,
                     remainder,
                 }
+            } else {
+                let new_remainder = function_s(env, w, c, remainder);
+
+                Join {
+                    id,
+                    parameters,
+                    body,
+                    remainder: new_remainder,
+                }
             };
 
             arena.alloc(new_join)
@@ -207,7 +209,7 @@ fn try_function_s<'a, 'i>(
 
     let new_stmt = function_s(env, w, c, stmt);
 
-    if stmt == new_stmt {
+    if std::ptr::eq(stmt, new_stmt) || stmt == new_stmt {
         stmt
     } else {
         insert_reset(env, w, x, Layout::Union(c.layout), new_stmt)
@@ -296,16 +298,11 @@ fn function_d_main<'a, 'i>(
                 _ => {
                     let (b, found) = function_d_main(env, x, c, continuation);
 
-                    // NOTE the &b != continuation is not found in the Lean source, but is required
-                    // otherwise we observe the same symbol being reset twice
                     let mut result = MutSet::default();
-                    if found
-                        || {
-                            occurring_variables_expr(expr, &mut result);
-                            !result.contains(&x)
-                        }
-                        || &b != continuation
-                    {
+                    if found || {
+                        occurring_variables_expr(expr, &mut result);
+                        !result.contains(&x)
+                    } {
                         let let_stmt = Let(*symbol, expr.clone(), *layout, b);
 
                         (arena.alloc(let_stmt), found)
@@ -416,10 +413,10 @@ fn function_d_main<'a, 'i>(
 
             let (b, found) = function_d_main(env, x, c, remainder);
 
-            env.jp_live_vars.remove(id);
-
             let (v, _found) = function_d_main(env, x, c, body);
 
+            env.jp_live_vars.remove(id);
+
             // If `found' == true`, then `Dmain b` must also have returned `(b, true)` since
             // we assume the IR does not have dead join points. So, if `x` is live in `j` (i.e., `v`),
             // then it must also live in `b` since `j` is reachable from `b` with a `jmp`.
@@ -466,6 +463,10 @@ fn function_r<'a, 'i>(env: &mut Env<'a, 'i>, stmt: &'a Stmt<'a>) -> &'a Stmt<'a>
             let mut new_branches = Vec::with_capacity_in(branches.len(), arena);
 
             // TODO for non-recursive unions there is no benefit
+            let benefits_from_reuse = match cond_layout {
+                Layout::Union(union_layout) => Some(union_layout),
+                _ => None,
+            };
 
             for (tag, info, body) in branches.iter() {
                 let temp = function_r(env, body);
@@ -477,7 +478,6 @@ fn function_r<'a, 'i>(env: &mut Env<'a, 'i>, stmt: &'a Stmt<'a>) -> &'a Stmt<'a>
                         layout,
                         tag_id,
                     } => match layout {
-                        Layout::Union(UnionLayout::NonRecursive(_)) => temp,
                         Layout::Union(union_layout) if !union_layout.tag_is_null(*tag_id) => {
                             let ctor_info = CtorInfo {
                                 layout: *union_layout,
@@ -503,7 +503,6 @@ fn function_r<'a, 'i>(env: &mut Env<'a, 'i>, stmt: &'a Stmt<'a>) -> &'a Stmt<'a>
                         layout,
                         tag_id,
                     } => match layout {
-                        Layout::Union(UnionLayout::NonRecursive(_)) => temp,
                         Layout::Union(union_layout) if !union_layout.tag_is_null(*tag_id) => {
                             let ctor_info = CtorInfo {
                                 layout: *union_layout,
@@ -537,13 +536,14 @@ fn function_r<'a, 'i>(env: &mut Env<'a, 'i>, stmt: &'a Stmt<'a>) -> &'a Stmt<'a>
         } => {
             env.jp_live_vars.insert(*id, LiveVarSet::default());
 
-            let v = function_r(env, body);
+            let body_live_vars = collect_stmt(body, &env.jp_live_vars, LiveVarSet::default());
 
-            let body_live_vars = collect_stmt(v, &env.jp_live_vars, LiveVarSet::default());
             env.jp_live_vars.insert(*id, body_live_vars);
 
             let b = function_r(env, remainder);
 
+            let v = function_r(env, body);
+
             env.jp_live_vars.remove(id);
 
             let join = Join {