[Fix] Properly demote to AoS for variable in for loop when body is an inlined function

[WardBrian]

Submission Checklist

• [x] Run unit tests
• Documentation
  • [x] OR, no user-facing changes were made

Release notes

Fix a bug in the memory pattern optimization where a for loop generated for the function inliner would prevent detection of for loops higher in the control flow graph.

Initially reported by @hsbadr for the rstanarm polr model on the forums here

Copyright and Licensing

By submitting this pull request, the copyright holder is agreeing to license the submitted work under the BSD 3-clause license (https://opensource.org/licenses/BSD-3-Clause)

[hsbadr]

@WardBrian Another one with EpiNow2 R packages when optimizations are enabled:

stanExports_estimate_infections.h(4545): error: identifier "inline_update_Rt_R_sym460__" is undefined
                                            inline_update_Rt_R_sym460__);
                                            ^

[WardBrian]

@hsbadr can you point me toward the Stan code for that model?

[hsbadr]

https://github.com/epiforecasts/EpiNow2/tree/master/inst/stan

[SteveBronder]

@hsbadr did that error happen before this PR?

[hsbadr]

did that error happen before this PR?

I didn't try to build EpiNow2 with stanc3 O1 optimizations before this PR. Should I test it?

[hsbadr]

@SteveBronder It fails with and without this PR if O1 optimizations are enabled. Otherwise, it compiles successfully. So, it's an issue with stanc3 optimizations, not related to this PR.

[WardBrian]

@SteveBronder it's an issue with if the name of the argument before inlining is the same as a variable later in the function.

MRE:

functions {
  vector foo(vector oR) {
    int ot = num_elements(oR);

    vector[ot] R = oR;

    return (R);
  }
}
data {
  int N;
}
transformed parameters {
  vector[N] R;
  vector[N] out;
  out = foo(R);
}

[WardBrian]

This generates code like

 data vector[0] inline_foo_return_sym1__;
  {
    int inline_foo_ot_sym2__;
    inline_foo_ot_sym2__ = num_elements(inline_foo_R_sym3__);
    FnValidateSize__("R", "ot", inline_foo_ot_sym2__);
    vector[inline_foo_ot_sym2__] inline_foo_R_sym3__;
    inline_foo_R_sym3__ = inline_foo_R_sym3__;
    inline_foo_return_sym1__ = inline_foo_R_sym3__;
  }
  out = inline_foo_return_sym1__;

but it should generate code like

data vector[0] inline_foo_return_sym1__;
  {
    int inline_foo_ot_sym2__;
    inline_foo_ot_sym2__ = num_elements(R_renamed);
    FnValidateSize__("R", "ot", inline_foo_ot_sym2__);
    vector[inline_foo_ot_sym2__] inline_foo_R_sym3__;
  }
  out = R_renamed;