add basics of stack-stored arguments

this requires some changes regarding the const-ability of the passed
nodes into codegen.

src/codegen.zig

@@ -389,7 +389,7 @@ pub const Codegen = struct {
     fn genNode(
         self: *Codegen,
         mod: llvm.LLVMModuleRef,
-        node: *const ast.Node,
+        node: *ast.Node,
     ) !void {
         switch (node.*) {
             .Root => @panic("Should not have gotten Root"),
@@ -430,6 +430,20 @@ pub const Codegen = struct {
                 var builder = llvm.LLVMCreateBuilder();
                 llvm.LLVMPositionBuilderAtEnd(builder, entry);
 
+                // to have the ability to mutate parameters, we must allocate them on
+                // the stack
+                for (params_slice) |param_node, idx| {
+                    var param = fn_sym.parameters.get(param_node.name.lexeme).?.value;
+
+                    const name_cstr = try std.cstr.addNullByte(self.allocator, param_node.name.lexeme);
+                    errdefer self.allocator.free(name_cstr);
+
+                    var alloca = llvm.LLVMBuildAlloca(builder, try self.typeToLLVM(param.typ), name_cstr.ptr);
+                    param.llvm_alloca = alloca;
+
+                    // TODO store register into stack param
+                }
+
                 self.ctx.setScope(fn_sym.scope);
                 defer self.ctx.dumpScope();
 
@@ -480,9 +494,9 @@ pub const Codegen = struct {
         var mod = llvm.LLVMModuleCreateWithName(c"awoo").?;
         defer llvm.LLVMDisposeModule(mod);
 
-        for (root.Root.toSlice()) |child| {
+        var root_slice = root.Root.toSlice();
-            std.debug.warn("cgen: gen {}\n", @tagName(child));
+        for (root_slice) |_, idx| {
-            try self.genNode(mod, &child);
+            try self.genNode(mod, &root_slice[idx]);
         }
 
         var err: ?[*]u8 = null;

src/comp_ctx.zig

@@ -79,6 +79,7 @@ pub const Scope = struct {
 
 pub const Parameter = struct {
     idx: usize,
+    name: []const u8,
     typ: SymbolUnderlyingType,
     alloca: ?llvm.LLVMValueRef = null,
 };
@@ -271,6 +272,7 @@ pub const CompilationContext = struct {
 
         for (decl.params.toSlice()) |param, idx| {
             _ = try param_map.put(param.name.lexeme, Parameter{
+                .name = param.name.lexeme,
                 .idx = idx,
                 .typ = param_types.at(idx),
             });