Tessera Pattern Matching with Struct Arguments

[jessicacotturone21]

The goal of this pull request is to allow for more pattern matching to occur by eliminating intermediate stores when we have struct arguments and returns. We also allow users to specify whether arguments are byref in the source code (as well as the size of the arguments), and any arguments specified as byref will be loaded and converted to byval in our tessera passes.

The user can now specify that an argument is byref like this:
tessera_op = eigen.inv(x: byref, sizeof(Mat))
where Mat is a struct and x is the matrix we want to take the inverse of.

Previously, after running the llvm-to-tessera pass and pulling out the sret argument, we would end up with something that looks like this:

%3 = tessera.call @eigen.inv(%2)
llvm.store %3, %1
%4 = tessera.call @eigen.inv(%1)

By loading the struct value from the pointer if it is byref and checking that the tessera.call op does not capture the pointer, we can perform store-to-load forwarding with the polygeist-mem2reg pass and end up with:

%3 = tessera.call @eigen.inv(%2)
%4 = tessera.call @eigen.inv(%3)

which our PDL pattern can match. This pull request updates the polygeist-mem2reg pass with additional type conversion logic and adds a canonicalization on tessera calls to allow this to happen.

Any operands that were changed from pointers to loaded values are kept track of and new llvm.alloca instances are created and pointer operands are reinserted when lowering back to LLVM.

The MemoryEffectOpInterface has also been implemented and pure_tessera_ops added, so that a user can declare a function as side effect free. This will allow for the elimination of lingering tessera.call ops that remain after the optimization rewrite has been performed.

[wsmoses]

you also need to check nocapture, and it can be readonly or readnone

[wsmoses]

consider a fn

double* pointeradd(double* x, int y) {
   return &x[y];
}

we could define an opt pointeradd(pointeradd(x, y), z) -> pointeradd(x, y+z)

double x[10] -> double* [ptr]

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 25.47%. Comparing base (aeecbf9) to head (cb0df8e).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2437   +/-   ##
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  Coverage   25.47%   25.47%           
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  Files         220      220           
  Lines       44600    44600           
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  Hits        11364    11364           
  Misses      33236    33236           

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