From d0ecd1238a34bf66b5099fb0492767b257b4fd8a Mon Sep 17 00:00:00 2001
From: Chris Fallin <chris@cfallin.org>
Date: Tue, 29 Nov 2022 00:58:55 -0800
Subject: [PATCH] WIP.

---
 src/backend/localify.rs |   4 +-
 src/backend/mod.rs      | 127 +++++++++++++++++++++++++++++++++++++++-
 src/backend/stackify.rs |   3 +
 src/ir.rs               |  13 ++++
 4 files changed, 142 insertions(+), 5 deletions(-)

diff --git a/src/backend/localify.rs b/src/backend/localify.rs
index 34902c3..44e526f 100644
--- a/src/backend/localify.rs
+++ b/src/backend/localify.rs
@@ -10,8 +10,8 @@ use std::collections::{HashMap, HashSet};
 
 #[derive(Clone, Debug, Default)]
 pub struct Localifier {
-    values: PerEntity<Value, SmallVec<[Local; 2]>>,
-    locals: EntityVec<Local, Type>,
+    pub values: PerEntity<Value, SmallVec<[Local; 2]>>,
+    pub locals: EntityVec<Local, Type>,
 }
 
 impl Localifier {
diff --git a/src/backend/mod.rs b/src/backend/mod.rs
index 8cf332e..c9d954d 100644
--- a/src/backend/mod.rs
+++ b/src/backend/mod.rs
@@ -1,9 +1,10 @@
 //! Backend: IR to Wasm.
 
 use crate::cfg::CFGInfo;
-use crate::ir::FunctionBody;
+use crate::ir::{FunctionBody, Value};
 use crate::passes::rpo::RPO;
 use anyhow::Result;
+use std::borrow::Cow;
 
 pub mod stackify;
 use stackify::{Context as StackifyContext, WasmBlock};
@@ -41,7 +42,127 @@ impl<'a> WasmBackend<'a> {
         })
     }
 
-    pub fn compile(&self) -> Result<Vec<u8>> {
-        Ok(vec![])
+    pub fn compile(&self) -> Result<wasm_encoder::Function> {
+        let mut func = wasm_encoder::Function::new(
+            self.locals
+                .locals
+                .values()
+                .map(|&ty| (1, wasm_encoder::ValType::from(ty)))
+                .collect::<Vec<_>>(),
+        );
+
+        for block in &self.ctrl {
+            self.lower_block(block, &mut func);
+        }
+
+        // If the last block was a Block, Loop or If, then the type
+        // may not match, so end with an Unreachable.
+        match self.ctrl.last() {
+            Some(&WasmBlock::Block { .. })
+            | Some(&WasmBlock::Loop { .. })
+            | Some(&WasmBlock::If { .. }) => {
+                func.instruction(&wasm_encoder::Instruction::Unreachable);
+            }
+            _ => {}
+        }
+
+        Ok(func)
+    }
+
+    fn lower_block(&self, block: &WasmBlock<'_>, func: &mut wasm_encoder::Function) {
+        match block {
+            WasmBlock::Block { body, .. } => {
+                func.instruction(&wasm_encoder::Instruction::Block(
+                    wasm_encoder::BlockType::Empty,
+                ));
+                for sub_block in &body[..] {
+                    self.lower_block(sub_block, func);
+                }
+                func.instruction(&wasm_encoder::Instruction::End);
+            }
+            WasmBlock::Loop { body, .. } => {
+                func.instruction(&wasm_encoder::Instruction::Loop(
+                    wasm_encoder::BlockType::Empty,
+                ));
+                for sub_block in &body[..] {
+                    self.lower_block(sub_block, func);
+                }
+                func.instruction(&wasm_encoder::Instruction::End);
+            }
+            WasmBlock::Br { target } => {
+                func.instruction(&wasm_encoder::Instruction::Br(target.index()));
+            }
+            WasmBlock::If {
+                cond,
+                if_true,
+                if_false,
+            } => {
+                self.lower_value(*cond, func);
+                func.instruction(&wasm_encoder::Instruction::If(
+                    wasm_encoder::BlockType::Empty,
+                ));
+                for sub_block in &if_true[..] {
+                    self.lower_block(sub_block, func);
+                }
+                if if_false.len() > 0 {
+                    func.instruction(&wasm_encoder::Instruction::Else);
+                    for sub_block in &if_false[..] {
+                        self.lower_block(sub_block, func);
+                    }
+                }
+                func.instruction(&wasm_encoder::Instruction::End);
+            }
+            WasmBlock::Select {
+                selector,
+                targets,
+                default,
+            } => {
+                self.lower_value(*selector, func);
+                func.instruction(&wasm_encoder::Instruction::BrTable(
+                    Cow::Owned(
+                        targets
+                            .iter()
+                            .map(|label| label.index())
+                            .collect::<Vec<_>>(),
+                    ),
+                    default.index(),
+                ));
+            }
+            WasmBlock::Leaf { block } => {
+                for &inst in &self.body.blocks[*block].insts {
+                    self.lower_inst(inst, func);
+                }
+            }
+            WasmBlock::BlockParams { from, to } => {
+                debug_assert_eq!(from.len(), to.len());
+                for &from in from.iter() {
+                    self.lower_value(from, func);
+                }
+                for &(_, to) in to.iter().rev() {
+                    self.lower_set_value(to, func);
+                }
+            }
+            WasmBlock::Return { values } => {
+                for &value in &values[..] {
+                    self.lower_value(value, func);
+                }
+                func.instruction(&wasm_encoder::Instruction::Return);
+            }
+            WasmBlock::Unreachable => {
+                func.instruction(&wasm_encoder::Instruction::Unreachable);
+            }
+        }
+    }
+
+    fn lower_value(&self, value: Value, func: &mut wasm_encoder::Function) {
+        todo!()
+    }
+
+    fn lower_set_value(&self, value: Value, func: &mut wasm_encoder::Function) {
+        todo!()
+    }
+
+    fn lower_inst(&self, value: Value, func: &mut wasm_encoder::Function) {
+        todo!()
     }
 }
diff --git a/src/backend/stackify.rs b/src/backend/stackify.rs
index 203de6d..90bd6ee 100644
--- a/src/backend/stackify.rs
+++ b/src/backend/stackify.rs
@@ -67,6 +67,9 @@ impl WasmLabel {
     fn add(&self, extra: usize) -> WasmLabel {
         WasmLabel(self.0.checked_add(u32::try_from(extra).unwrap()).unwrap())
     }
+    pub fn index(&self) -> u32 {
+        self.0
+    }
 }
 
 pub struct Context<'a, 'b> {
diff --git a/src/ir.rs b/src/ir.rs
index 1bc1d4c..5fafc10 100644
--- a/src/ir.rs
+++ b/src/ir.rs
@@ -39,6 +39,19 @@ impl std::fmt::Display for Type {
     }
 }
 
+impl From<Type> for wasm_encoder::ValType {
+    fn from(ty: Type) -> wasm_encoder::ValType {
+        match ty {
+            Type::I32 => wasm_encoder::ValType::I32,
+            Type::I64 => wasm_encoder::ValType::I64,
+            Type::F32 => wasm_encoder::ValType::F32,
+            Type::F64 => wasm_encoder::ValType::F64,
+            Type::V128 => wasm_encoder::ValType::V128,
+            Type::FuncRef => wasm_encoder::ValType::FuncRef,
+        }
+    }
+}
+
 declare_entity!(Signature, "sig");
 declare_entity!(Func, "func");
 declare_entity!(Block, "block");