类型推导

这两篇博客 (, 2) 描述了 Julia 的类型推导实现。

You can start a Julia session, edit (for example to insert print statements), and then replace Core.Compiler in your running session by navigating to base/compiler and executing include("compiler.jl"). This trick typically leads to much faster development than if you rebuild Julia for each change.

If your debugging adventures require a MethodInstance, you can look it up by calling Core.Compiler.code_for_method using many of the variables above. A object may be obtained with

Much of the hardest work for inlining runs in inlining_pass. However, if your question is “why didn’t my function inline?” then you will most likely be interested in isinlineable and its primary callee, inline_worthy. isinlineable handles a number of special cases (e.g., critical functions like next and done, incorporating a bonus for functions that return tuples, etc.). The main decision-making happens in inline_worthy, which returns true if the function should be inlined.

The foundation of the cost-model is a lookup table, implemented in add_tfunc and its callers, that assigns an estimated cost (measured in CPU cycles) to each of Julia’s intrinsic functions. These costs are based on (see Agner Fog’s analysis for more detail).

We supplement this low-level lookup table with a number of special cases. For example, an :invoke expression (a call for which all input and output types were inferred in advance) is assigned a fixed cost (currently 20 cycles). In contrast, a :call expression, for functions other than intrinsics/builtins, indicates that the call will require dynamic dispatch, in which case we assign a cost set by Params.inline_nonleaf_penalty (currently set at 1000). Note that this is not a “first-principles” estimate of the raw cost of dynamic dispatch, but a mere heuristic indicating that dynamic dispatch is extremely expensive.

The output is a Vector{Int} holding the estimated cost of each statement in . Note that ci includes the consequences of inlining callees, and consequently the costs do too.