1 files changed, 31 insertions, 18 deletions

diff --git a/src/compile.zig b/src/compile.zig
index 6a79efd..9513a93 100644
--- a/src/compile.zig
+++ b/src/compile.zig
@@ -15,6 +15,7 @@ pub const Instr = struct {
         constant: Constant,
         bin_op: BinOp,
         print: Print,
+        discard: Discard,
     };
 
     pub const Constant = struct {
@@ -43,6 +44,7 @@ pub const Instr = struct {
     };
 
     pub const Print = struct {
+        dest: VReg,
         arg: VReg,
 
         pub fn sources(self: Print) Sources {
@@ -50,6 +52,14 @@ pub const Instr = struct {
         }
     };
 
+    pub const Discard = struct {
+        vreg: VReg,
+
+        pub fn sources(self: Discard) Sources {
+            return Sources.fromSlice(&.{self.vreg}) catch unreachable;
+        }
+    };
+
     pub fn sources(self: Instr) Sources {
         return switch (self.type) {
             inline else => |instr| instr.sources(),
@@ -58,8 +68,8 @@ pub const Instr = struct {
 
     pub fn dest(self: *const Instr) ?VReg {
         return switch (self.type) {
-            inline .constant, .bin_op => |s| s.dest,
-            inline .print => null,
+            inline .constant, .bin_op, .print => |s| s.dest,
+            // inline .x => null,
         };
     }
 
@@ -69,13 +79,16 @@ pub const Instr = struct {
 pub const Block = struct {
     // arguments: []Reg,
     instrs: []Instr,
-    vreg_last_use: std.AutoHashMap(VReg, usize),
+    vreg_last_use: std.AutoHashMap(usize, std.ArrayList(VReg)),
 
     fn init(allocator: Allocator, instrs: []Instr) !Block {
-        var vreg_last_use: std.AutoHashMap(VReg, usize) = .init(allocator);
+        var vreg_last_use: std.AutoHashMap(usize, std.ArrayList(VReg)) = .init(allocator);
         for (0.., instrs) |i, instr| {
-            for (instr.sources().slice()) |src|
-                try vreg_last_use.put(src, i);
+            for (instr.sources().slice()) |src| {
+                const kv = try vreg_last_use.getOrPut(i);
+                if (!kv.found_existing) kv.value_ptr.* = .init(allocator);
+                try kv.value_ptr.append(src);
+            }
         }
         return .{
             .instrs = instrs,
@@ -112,7 +125,10 @@ const CompileContext = struct {
 
     fn compileStmt(self: *Self, stmt: parse.Stmt) !void {
         switch (stmt.type) {
-            .expr => |expr| _ = try self.compileExpr(expr),
+            .expr => |expr| try self.addInstr(.{
+                .loc = stmt.loc,
+                .type = .{ .discard = .{ .vreg = try self.compileExpr(expr) } },
+            }),
         }
     }
 
@@ -142,18 +158,15 @@ const CompileContext = struct {
                 });
             },
             .call => |call| {
-                if (call.proc.type == .identifier and
-                    std.mem.eql(u8, call.proc.loc.getIdent(self.source), "print"))
-                {
-                    const arg = try self.compileExpr(call.arg);
-                    try self.addInstr(.{
-                        .loc = expr.loc,
-                        .type = .{ .print = .{ .arg = arg } },
-                    });
-                    // BUG: we're returning a bogus virtual register that we didn't write to
-                } else {
+                if (call.proc.type != .identifier or
+                    !std.mem.eql(u8, call.proc.loc.getIdent(self.source), "print"))
                     return error.CantCallAnythingButPrint;
-                }
+
+                const arg = try self.compileExpr(call.arg);
+                try self.addInstr(.{
+                    .loc = expr.loc,
+                    .type = .{ .print = .{ .dest = dest, .arg = arg } },
+                });
             },
             .identifier => return error.CantCompileIdentifierExpr,
         }