assignOp

fn assignOp(
    gz: *GenZir,
    scope: *Scope,
    infix_node: Ast.Node.Index,
    op_inst_tag: Zir.Inst.Tag,
) InnerError!void {
    try emitDbgNode(gz, infix_node);
    const astgen = gz.astgen;
    const tree = astgen.tree;

    const lhs_node, const rhs_node = tree.nodeData(infix_node).node_and_node;
    const lhs_ptr = try lvalExpr(gz, scope, lhs_node);

    const cursor = switch (op_inst_tag) {
        .add, .sub, .mul, .div, .mod_rem => maybeAdvanceSourceCursorToMainToken(gz, infix_node),
        else => undefined,
    };
    const lhs = try gz.addUnNode(.load, lhs_ptr, infix_node);

    const rhs_res_ty = switch (op_inst_tag) {
        .add,
        .sub,
        => try gz.add(.{
            .tag = .extended,
            .data = .{ .extended = .{
                .opcode = .inplace_arith_result_ty,
                .small = @intFromEnum(@as(Zir.Inst.InplaceOp, switch (op_inst_tag) {
                    .add => .add_eq,
                    .sub => .sub_eq,
                    else => unreachable,
                })),
                .operand = @intFromEnum(lhs),
            } },
        }),
        else => try gz.addUnNode(.typeof, lhs, infix_node), // same as LHS type
    };
    // Not `coerced_ty` since `add`/etc won't coerce to this type.
    const rhs = try expr(gz, scope, .{ .rl = .{ .ty = rhs_res_ty } }, rhs_node);

    switch (op_inst_tag) {
        .add, .sub, .mul, .div, .mod_rem => {
            try emitDbgStmt(gz, cursor);
        },
        else => {},
    }
    const result = try gz.addPlNode(op_inst_tag, infix_node, Zir.Inst.Bin{
        .lhs = lhs,
        .rhs = rhs,
    });
    _ = try gz.addPlNode(.store_node, infix_node, Zir.Inst.Bin{
        .lhs = lhs_ptr,
        .rhs = result,
    });
}