From f81b5bfbe977f0ef73a7ab0392b5395278f41b66 Mon Sep 17 00:00:00 2001
From: Chris Fallin <chris@cfallin.org>
Date: Sat, 25 Feb 2023 11:31:49 -0800
Subject: [PATCH] Fuel mechanism to help debug opts

---
 src/ir/func.rs          |  9 +++++----
 src/passes.rs           | 15 +++++++++++++++
 src/passes/basic_opt.rs | 25 +++++++++++++++++++------
 3 files changed, 39 insertions(+), 10 deletions(-)

diff --git a/src/ir/func.rs b/src/ir/func.rs
index 826173a..aefd907 100644
--- a/src/ir/func.rs
+++ b/src/ir/func.rs
@@ -3,6 +3,7 @@ use crate::cfg::CFGInfo;
 use crate::entity::{EntityRef, EntityVec, PerEntity};
 use crate::frontend::parse_body;
 use crate::ir::SourceLoc;
+use crate::passes::Fuel;
 use anyhow::Result;
 
 #[derive(Clone, Debug)]
@@ -32,10 +33,10 @@ impl<'a> FuncDecl<'a> {
         }
     }
 
-    pub fn optimize(&mut self) {
+    pub fn optimize(&mut self, fuel: &mut Fuel) {
         match self {
             FuncDecl::Body(_, _, body) => {
-                body.optimize();
+                body.optimize(fuel);
             }
             _ => {}
         }
@@ -131,9 +132,9 @@ impl FunctionBody {
         }
     }
 
-    pub fn optimize(&mut self) {
+    pub fn optimize(&mut self, fuel: &mut Fuel) {
         let cfg = crate::cfg::CFGInfo::new(self);
-        crate::passes::basic_opt::gvn(self, &cfg);
+        crate::passes::basic_opt::gvn(self, &cfg, fuel);
         crate::passes::resolve_aliases::run(self);
         crate::passes::ssa::run(self, &cfg);
     }
diff --git a/src/passes.rs b/src/passes.rs
index 46aa889..11dc04c 100644
--- a/src/passes.rs
+++ b/src/passes.rs
@@ -7,3 +7,18 @@ pub mod maxssa;
 pub mod resolve_aliases;
 pub mod ssa;
 pub mod trace;
+
+#[derive(Clone, Debug)]
+pub struct Fuel {
+    pub remaining: u64,
+}
+impl Fuel {
+    pub fn consume(&mut self) -> bool {
+        if self.remaining == 0 {
+            false
+        } else {
+            self.remaining -= 1;
+            true
+        }
+    }
+}
diff --git a/src/passes/basic_opt.rs b/src/passes/basic_opt.rs
index dd2e9d5..828fb0f 100644
--- a/src/passes/basic_opt.rs
+++ b/src/passes/basic_opt.rs
@@ -4,19 +4,28 @@ use crate::cfg::CFGInfo;
 use crate::interp::{const_eval, ConstVal};
 use crate::ir::*;
 use crate::passes::dom_pass::{dom_pass, DomtreePass};
+use crate::passes::Fuel;
 use crate::scoped_map::ScopedMap;
 use crate::Operator;
 
-pub fn gvn(body: &mut FunctionBody, cfg: &CFGInfo) {
-    dom_pass::<GVNPass>(body, cfg, &mut GVNPass::default());
+pub fn gvn(body: &mut FunctionBody, cfg: &CFGInfo, fuel: &mut Fuel) {
+    dom_pass::<GVNPass<'_>>(
+        body,
+        cfg,
+        &mut GVNPass {
+            map: ScopedMap::default(),
+            fuel,
+        },
+    );
 }
 
-#[derive(Clone, Debug, Default)]
-struct GVNPass {
+#[derive(Debug)]
+struct GVNPass<'a> {
     map: ScopedMap<ValueDef, Value>,
+    fuel: &'a mut Fuel,
 }
 
-impl DomtreePass for GVNPass {
+impl<'a> DomtreePass for GVNPass<'a> {
     fn enter(&mut self, block: Block, body: &mut FunctionBody) {
         self.map.push_level();
         self.optimize(block, body);
@@ -34,10 +43,14 @@ fn value_is_pure(value: Value, body: &FunctionBody) -> bool {
     }
 }
 
-impl GVNPass {
+impl<'a> GVNPass<'a> {
     fn optimize(&mut self, block: Block, body: &mut FunctionBody) {
         let mut i = 0;
         while i < body.blocks[block].insts.len() {
+            if !self.fuel.consume() {
+                return;
+            }
+
             let inst = body.blocks[block].insts[i];
             i += 1;
             if value_is_pure(inst, body) {