1 files changed, 142 insertions, 0 deletions
diff --git a/src/codegen/wasm.zig b/src/codegen/wasm.zig
new file mode 100644
index 0000000000..4ea8838409
--- /dev/null
+++ b/src/codegen/wasm.zig
@@ -0,0 +1,142 @@
+const std = @import("std");
+const Allocator = std.mem.Allocator;
+const ArrayList = std.ArrayList;
+const assert = std.debug.assert;
+const leb = std.debug.leb;
+const mem = std.mem;
+
+const Module = @import("../Module.zig");
+const Decl = Module.Decl;
+const Inst = @import("../ir.zig").Inst;
+const Type = @import("../type.zig").Type;
+const Value = @import("../value.zig").Value;
+
+fn genValtype(ty: Type) u8 {
+    return switch (ty.tag()) {
+        .u32, .i32 => 0x7F,
+        .u64, .i64 => 0x7E,
+        .f32 => 0x7D,
+        .f64 => 0x7C,
+        else => @panic("TODO: Implement more types for wasm."),
+    };
+}
+
+pub fn genFunctype(buf: *ArrayList(u8), decl: *Decl) !void {
+    const ty = decl.typed_value.most_recent.typed_value.ty;
+    const writer = buf.writer();
+
+    // functype magic
+    try writer.writeByte(0x60);
+
+    // param types
+    try leb.writeULEB128(writer, @intCast(u32, ty.fnParamLen()));
+    if (ty.fnParamLen() != 0) {
+        const params = try buf.allocator.alloc(Type, ty.fnParamLen());
+        defer buf.allocator.free(params);
+        ty.fnParamTypes(params);
+        for (params) |param_type| try writer.writeByte(genValtype(param_type));
+    }
+
+    // return type
+    const return_type = ty.fnReturnType();
+    switch (return_type.tag()) {
+        .void, .noreturn => try leb.writeULEB128(writer, @as(u32, 0)),
+        else => {
+            try leb.writeULEB128(writer, @as(u32, 1));
+            try writer.writeByte(genValtype(return_type));
+        },
+    }
+}
+
+pub fn genCode(buf: *ArrayList(u8), decl: *Decl) !void {
+    assert(buf.items.len == 0);
+    const writer = buf.writer();
+
+    // Reserve space to write the size after generating the code
+    try buf.resize(5);
+
+    // Write the size of the locals vec
+    // TODO: implement locals
+    try leb.writeULEB128(writer, @as(u32, 0));
+
+    // Write instructions
+    // TODO: check for and handle death of instructions
+    const tv = decl.typed_value.most_recent.typed_value;
+    const mod_fn = tv.val.cast(Value.Payload.Function).?.func;
+    for (mod_fn.analysis.success.instructions) |inst| try genInst(buf, decl, inst);
+
+    // Write 'end' opcode
+    try writer.writeByte(0x0B);
+
+    // Fill in the size of the generated code to the reserved space at the
+    // beginning of the buffer.
+    const size = buf.items.len - 5 + decl.fn_link.wasm.?.idx_refs.items.len * 5;
+    leb.writeUnsignedFixed(5, buf.items[0..5], @intCast(u32, size));
+}
+
+fn genInst(buf: *ArrayList(u8), decl: *Decl, inst: *Inst) !void {
+    return switch (inst.tag) {
+        .call => genCall(buf, decl, inst.castTag(.call).?),
+        .constant => genConstant(buf, decl, inst.castTag(.constant).?),
+        .dbg_stmt => {},
+        .ret => genRet(buf, decl, inst.castTag(.ret).?),
+        .retvoid => {},
+        else => error.TODOImplementMoreWasmCodegen,
+    };
+}
+
+fn genConstant(buf: *ArrayList(u8), decl: *Decl, inst: *Inst.Constant) !void {
+    const writer = buf.writer();
+    switch (inst.base.ty.tag()) {
+        .u32 => {
+            try writer.writeByte(0x41); // i32.const
+            try leb.writeILEB128(writer, inst.val.toUnsignedInt());
+        },
+        .i32 => {
+            try writer.writeByte(0x41); // i32.const
+            try leb.writeILEB128(writer, inst.val.toSignedInt());
+        },
+        .u64 => {
+            try writer.writeByte(0x42); // i64.const
+            try leb.writeILEB128(writer, inst.val.toUnsignedInt());
+        },
+        .i64 => {
+            try writer.writeByte(0x42); // i64.const
+            try leb.writeILEB128(writer, inst.val.toSignedInt());
+        },
+        .f32 => {
+            try writer.writeByte(0x43); // f32.const
+            // TODO: enforce LE byte order
+            try writer.writeAll(mem.asBytes(&inst.val.toFloat(f32)));
+        },
+        .f64 => {
+            try writer.writeByte(0x44); // f64.const
+            // TODO: enforce LE byte order
+            try writer.writeAll(mem.asBytes(&inst.val.toFloat(f64)));
+        },
+        .void => {},
+        else => return error.TODOImplementMoreWasmCodegen,
+    }
+}
+
+fn genRet(buf: *ArrayList(u8), decl: *Decl, inst: *Inst.UnOp) !void {
+    try genInst(buf, decl, inst.operand);
+}
+
+fn genCall(buf: *ArrayList(u8), decl: *Decl, inst: *Inst.Call) !void {
+    const func_inst = inst.func.castTag(.constant).?;
+    const func_val = func_inst.val.cast(Value.Payload.Function).?;
+    const target = func_val.func.owner_decl;
+    const target_ty = target.typed_value.most_recent.typed_value.ty;
+
+    if (inst.args.len != 0) return error.TODOImplementMoreWasmCodegen;
+
+    try buf.append(0x10); // call
+
+    // The function index immediate argument will be filled in using this data
+    // in link.Wasm.flush().
+    try decl.fn_link.wasm.?.idx_refs.append(buf.allocator, .{
+        .offset = @intCast(u32, buf.items.len),
+        .decl = target,
+    });
+}