Assert in Mem2Reg.cpp due to pointer address space mismatch

func @_ZN2cl4sycl6detail7declptrINS0_4itemILi2ELb1EEEEEPT_v() -> !llvm.ptr<struct<(struct<(struct<(struct<(array<2 x i64>)>)>, struct<(struct<(array<2 x i64>)>)>, struct<(struct<(array<2 x i64>)>)>)>)>> attributes {llvm.linkage = #llvm.linkage<linkonce_odr>} {
  %false = arith.constant false
  %true = arith.constant true
  %0 = memref.alloca() : memref<i1>
  memref.store %true, %0[] : memref<i1>
  %1 = memref.alloca() : memref<!llvm.ptr<struct<(struct<(struct<(struct<(array<2 x i64>)>)>, struct<(struct<(array<2 x i64>)>)>, struct<(struct<(array<2 x i64>)>)>)>)>>>
  %2 = memref.load %0[] : memref<i1>
  %3 = memref.load %1[] : memref<!llvm.ptr<struct<(struct<(struct<(struct<(array<2 x i64>)>)>, struct<(struct<(array<2 x i64>)>)>, struct<(struct<(array<2 x i64>)>)>)>)>>>
  %4:2 = scf.if %true -> (i1, !llvm.ptr<struct<(struct<(struct<(struct<(array<2 x i64>)>)>, struct<(struct<(array<2 x i64>)>)>, struct<(struct<(array<2 x i64>)>)>)>)>, 4>) {
    %6 = memref.load %0[] : memref<i1>
    %7:2 = scf.if %true -> (i1, !llvm.ptr<struct<(struct<(struct<(struct<(array<2 x i64>)>)>, struct<(struct<(array<2 x i64>)>)>, struct<(struct<(array<2 x i64>)>)>)>)>, 4>) {
      %8 = llvm.mlir.null : !llvm.ptr<struct<(struct<(struct<(struct<(array<2 x i64>)>)>, struct<(struct<(array<2 x i64>)>)>, struct<(struct<(array<2 x i64>)>)>)>)>, 4>
      memref.store %8, %1[] : memref<!llvm.ptr<struct<(struct<(struct<(struct<(array<2 x i64>)>)>, struct<(struct<(array<2 x i64>)>)>, struct<(struct<(array<2 x i64>)>)>)>)>>>
      memref.store %false, %0[] : memref<i1>
      scf.yield %false, %8 : i1, !llvm.ptr<struct<(struct<(struct<(struct<(array<2 x i64>)>)>, struct<(struct<(array<2 x i64>)>)>, struct<(struct<(array<2 x i64>)>)>)>)>, 4>
    } else {
      scf.yield %true, %3 : i1, !llvm.ptr<struct<(struct<(struct<(struct<(array<2 x i64>)>)>, struct<(struct<(array<2 x i64>)>)>, struct<(struct<(array<2 x i64>)>)>)>)>>
    }
    scf.yield %7#0, %7#1 : i1, !llvm.ptr<struct<(struct<(struct<(struct<(array<2 x i64>)>)>, struct<(struct<(array<2 x i64>)>)>, struct<(struct<(array<2 x i64>)>)>)>)>, 4>
  } else {
    scf.yield %true, %3 : i1, !llvm.ptr<struct<(struct<(struct<(struct<(array<2 x i64>)>)>, struct<(struct<(array<2 x i64>)>)>, struct<(struct<(array<2 x i64>)>)>)>)>>
  }
  %5 = memref.load %1[] : memref<!llvm.ptr<struct<(struct<(struct<(struct<(array<2 x i64>)>)>, struct<(struct<(array<2 x i64>)>)>, struct<(struct<(array<2 x i64>)>)>)>)>>>
  return %5 : !llvm.ptr<struct<(struct<(struct<(struct<(array<2 x i64>)>)>, struct<(struct<(array<2 x i64>)>)>, struct<(struct<(array<2 x i64>)>)>)>)>>
}

The above MLIR representation is related to below code, dumped at the entry to the first call to Mem2Reg pass.

template <typename T> T *declptr() { return static_cast<T *>(nullptr); }

processing the function using Mem2Reg results in below assert.

!llvm.ptr<struct<(struct<(struct<(struct<(array<2 x i64>)>)>, struct<(struct<(array<2 x i64>)>)>, struct<(struct<(array<2 x i64>)>)>)>)>> - !llvm.ptr<struct<(struct<(struct<(struct<(array<2 x i64>)>)>, struct<(struct<(array<2 x i64>)>)>, struct<(struct<(array<2 x i64>)>)>)>)>, 4>
mlir-clang: /home/m/Polygeist/lib/polygeist/Passes/Mem2Reg.cpp:641: {anonymous}::Mem2Reg::forwardStoreToLoad(mlir::Value, std::vector<long int, std::allocator<long int> >, llvm::SmallVectorImpl<mlir::Operation*>&)::<lambda(mlir::Block&, mlir::Value)>: Assertion `loadOp.getType() == lastVal.getType() && "mismatched load type"' failed.

The assert is related to mismatch between the address space of the pointer types in lastVal.getType() and loadType.getType.

Processing above as a stand alone C++ function does not result in the above assert. The assert is due to the pointer type being cached with address space of 4 in CodegenTypes::ConvertTypes while processing an earlier function.

To handle the assert above I considering 2 possible approaches:

• To limit the comparison to ElementType of the pointers and ignore the Address space of the pointer types. Something like below:
  Check equality and assert on loadOp.getType()->getElementType() == lastVal.getType()->getElementType().

• We could also consider applying the optimisation only when pointers at both load / store share similar address space.

I would appreciate any suggestions on above potential solutions or any other viable solution.

Regards,
Moadeli

Start at lib/polygeist/Passes/Mem2Reg.cpp:641 and trace forwardStoreToLoad, then inspect how CodegenTypes::ConvertTypes cached the pointer address space. Reproduce the supplied MLIR case and compare it with the standalone C++ function; done means the Mem2Reg pass handles the pointer address-space mismatch without triggering the assertion.