[PATCH] D73600: [Matrix] Add remark propagation along the inlined-at chain.

[Florian Hahn via Phabricator via llvm-commits]

fhahn created this revision.
fhahn added reviewers: anemet, Gerolf, thegameg, hfinkel, andrew.w.kaylor, LuoYuanke.
Herald added subscribers: tschuett, hiraditya.
Herald added a project: LLVM.

This patch adds support for propagating matrix expressions along the
inlined-at chain and emitting remarks at the traversed function scopes.

For a given function, we traverse the inlined-at chain for each
matrix instruction (= instructions with shape information). We collect
the matrix instructions in each DISubprogram we visit. This produces a
mapping of DISubprogram -> (List of matrix instructions visible in the
subpogram). We then generate remarks using the list of instructions for
each subprogram. This allows surfacing the remarks at a level useful to
users.

To motivate this new behavior, consider the example below. Without the
remark 'up-leveling', we would only get remarks in load.h and store.h,
but we cannot generate a remark describing the full expression in
toplevel.cpp, which is the place where the user has the best chance of
spotting/fixing potential problems.

With this patch, we generate a remark for the load in load.h, one for
the store in store.h and one for the complete expression in
toplevel.cpp. For a bigger example, please see remarks-inlining.ll.

  load.h:
  template <typename Ty, unsigned R, unsigned C> Matrix<Ty, R, C> load(Ty *Ptr) {
    Matrix<Ty, R, C> Result;
    Result.value = *reinterpret_cast <typename Matrix<Ty, R, C>::matrix_t *>(Ptr);
    return Result;
  }
  
  store.h:
  template <typename Ty, unsigned R, unsigned C> void store(Matrix<Ty, R, C> M1, Ty *Ptr) {
     *reinterpret_cast<typename decltype(M1)::matrix_t *>(Ptr) = M1.value;
  }
  
  toplevel.cpp
  void test(double *A, double *B, double *C) {
    store(add(load<double, 3, 5>(A), load<double, 3, 5>(B)), C);
  }

Please note that the current approach may create a lot of extra remarks.
Additional heuristics to cut-off the traversal can be implemented in the
future. For example, it might make sense to stop 'up-leveling' once all
matrix instructions are at the same debug location.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D73600

Files:
  llvm/lib/Transforms/Scalar/LowerMatrixIntrinsics.cpp
  llvm/test/Transforms/LowerMatrixIntrinsics/remarks-inlining.ll
  llvm/test/Transforms/LowerMatrixIntrinsics/remarks.ll

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