In Compile "InlineExternalDefinitions" doesn't work anymore in Mma v10 like in v9

Question

In Mma 9 using CompilationOptions -> {"InlineExternalDefinitions" -> True} inside of Compile inlined the values of the previously defined parameters used in the function to be compiled.

For example:

nPara = 3;
cf = Compile[{{x, _Real, 1}},
  Sum[x[[i]], {i, nPara}], 
  CompilationOptions -> {"InlineExternalDefinitions" -> True}
  ]

resultes in:

and works flawless as expected.

But in Mma 10 the output is:

And, as now the value of nPara is not known to the compiled function, the comiled function doesn't work anymore.

For such a simple function one can apply Whith as a workaround:

With[{nPara = nPara},
 Compile[{{x, _Real, 1}},
  Sum[x[[i]], {i, nPara}], 
  CompilationOptions -> {"InlineExternalDefinitions" -> True}
  ]
 ]

However, in bigger notebooks and with more complex functions this undocumented code break (or is a bug or a fix) causes bigger issues.

Does anyone know a more convenient or automated workaround to fix this problem?

Answer 1

It is unfortunate that this no longer works. I like metaprogramming, and I felt that inlining variables is a nice exercise, so I can share some functions with you that make things easier.

Your approach using With seems reasonable. I also saw you test an example using Evaluate, but relying on the fact that x[[i]] evaluates to x[[i]] if i not an integer and x has no value is quite bad.

You say that your approach using With will not work for more complicated cases. If the issue is that you want to use evaluation to determine the values of your parameters, you can use the following.

ClearAll@inlineEval
SetAttributes[inlineEval, HoldAll];
inlineEval[expr_, symbols__] :=
 Unevaluated[expr] /. 
  Thread[Rule[HoldPattern /@ Unevaluated[{symbols}], {symbols}]]

You can use it as follows. Let's set up a situation that is relatively hard to deal with to test it.

b := c[1, 2]
c[x_, y_] := x + y

Now we can do

cfu =
  inlineEval[
   Compile[{{x, _Integer}}, Sum[1, {i, x + b}]]
   ,
   b
   ];
cfu[3]

6

If you don't want to use evaluation, you can use the following.

SetAttributes[inlineAll, HoldAll]
inlineAll[expr_, symbols__Symbol] :=
  ReleaseHold[
   HoldComplete[expr] //.
    Flatten[Function[Null, {OwnValues@#, DownValues@#}, HoldAll] /@ 
      Unevaluated[{symbols}]]
   ];

Now you can also this, but note that you have to specify that c has to be inlined as well.

cfu2 =
  inlineAll[
   Compile[{{x, _Integer}}, Sum[1, {i, x + b}]]
   ,
   b, c
   ];
cfu2[3]

6

Note that both functions also with symbols that have DownValues, which is something I believe "InlineExternalDefinitions" could not deal with to begin with. The previous examples dealt only with constants, but here is an example where we inline a function.

f[x_] := Norm[x];
cfu3 =
  inlineAll[
   Compile[{{x, _Real, 1}}, f[x] + 3]
   ,
   f
   ];
cfu3[{1., 1.}] == Sqrt[2] + 3

True

This technique allows you to make large compiled functions, while maintaining readability. You could imagine that when compiled functions get too large, you simply let one compiled function call another compiled function, and optionally using "InlineCompiledFunctions". But I like this alternative :).

Related (but probably less nice than this)