Add LLDB pretty-printing

[alexreinking]

Pulling out changes from my rfactor work...

This PR adds some features for visualizing Halide's types in LLDB, which my IDE (CLion) uses. The IR printer supports a "summary" mode that replaces certain subexpressions / blocks with ellipses. This has greatly improved my debugging experience. I encourage others to add to this and tweak it.

[steven-johnson]

Any idea how this works with "naked" LLDB? If so, adding a comment would be nice.

[alexreinking]

This just installs pretty printers. So after loading the script via command script import ./tools/lldbhalide.py, it should just start using the IRPrinter functions to render Exprs and Stmts

[zvookin]

Can you add some documentation mention so folks know it exists? Perhaps in the README or maybe an added page in the Doxygen? I guess it's Halide internal devr only, but having a couple lines on it in docs means it will get used. Probably also worth writing down the command line flags to use it with straight command line lldb.

[alexreinking]

Can you add some documentation mention so folks know it exists? Perhaps in the README or maybe an added page in the Doxygen? I guess it's Halide internal devr only, but having a couple lines on it in docs means it will get used. Probably also worth writing down the command line flags to use it with straight command line lldb.

Of course -- I'll do that as I fix the indents I broke

[abadams]

Can you post some example lldb output with this enabled?

[steven-johnson]

Status?

[alexreinking]

Still in progress. I added a bunch more rules in a private branch and will need to update this PR

[alexreinking]

Can you post some example lldb output with this enabled?

I added some to the Testing readme in this PR, but here's a direct comparison. Let's debug correctness/bounds.cpp. I'll set a breakpoint at line 18:

Without the helpers, this is what I see in the debugger when inspecting the definition of h:

As you can see, this is completely useless. It is also the direct result of parsing frame variable h:

(lldb) frame variable h
(Halide::Func) h = {
  func = {
    contents = {
      strong = (ptr = 0x0000600003252f80)
      weak = nullptr
      idx = 0
    }
  }
  pipeline_ = {
    contents = (ptr = 0x0000000000000000)
  }
}

Now, if I do this again, but with the helpers loaded, I see something much more useful:

And indeed I can drill further down and see useful summaries of its definitions:

This is accessible from the command line, of course:

(lldb) frame variable h
(Halide::Internal::FunctionContents) $20 = {
  name = "h"
  origin_name = "h"
  output_types = size=1 {
    [0] = {
      type = halide_type_int bits=32 ' ' lanes=1
      handle_type = nullptr
    }
  }
  required_types = size=0 {}
  required_dims = -1
  args = size=2 {
    [0] = "x"
    [1] = "y"
  }
... lots more output ...