Bug in the VectorEmulateNarrowType logic

[banach-space]

Reproducer

func.func @vector_maskedload_i4_constant_mask(%passthru: vector<8xi4>) -> vector<8xi4> {
  %0 = memref.alloc() : memref<3x8xi4>
  %cst = arith.constant dense<0> : vector<8xi4>
  %mask = arith.constant dense<[false, true, true, true, true, false, false, false]> : vector<8xi1>
  %c0 = arith.constant 0 : index
  %1 = vector.maskedload %0[%c0, %c0], %mask, %passthru :
    memref<3x8xi4>, vector<8xi1>, vector<8xi4> into vector<8xi4>
  return %1 : vector<8xi4>
}

To run

mlir-opt --test-emulate-narrow-int="arith-compute-bitwidth=1 memref-load-bitwidth=8" --cse --split-input-file

Error

ATM, this example will trigger an infinite loop due to this while cond not supporting arith.constant. Once that's fixed, I get this error:

file.mlir:1 offset :8:8: error: failed to legalize operation 'vector.maskedload' that was explicitly marked illegal
  %1 = vector.maskedload %0[%c0, %c0], %mask, %passthru :
       ^

CC @lialan

[llvmbot]

@llvm/issue-subscribers-mlir

Author: Andrzej Warzyński (banach-space)

**Reproducer**

func.func @<!-- -->vector_cst_maskedload_i4(%passthru: vector&lt;8xi4&gt;) -&gt; vector&lt;8xi4&gt; {
  %0 = memref.alloc() : memref&lt;3x8xi4&gt;
  %cst = arith.constant dense&lt;0&gt; : vector&lt;8xi4&gt;
  %mask = arith.constant dense&lt;[false, true, true, true, true, false, false, false]&gt; : vector&lt;8xi1&gt;
  %c0 = arith.constant 0 : index
  %1 = vector.maskedload %0[%c0, %c0], %mask, %passthru :
    memref&lt;3x8xi4&gt;, vector&lt;8xi1&gt;, vector&lt;8xi4&gt; into vector&lt;8xi4&gt;
  return %1 : vector&lt;8xi4&gt;
}

To run

mlir-opt --test-emulate-narrow-int="arith-compute-bitwidth=1 memref-load-bitwidth=8" --cse --split-input-file

Error

ATM, this example will trigger an infinite loop due to this while cond not supporting arith.constant. Once that's fixed, I get this error:

file.mlir:1 offset :8:8: error: failed to legalize operation 'vector.maskedload' that was explicitly marked illegal
  %1 = vector.maskedload %0[%c0, %c0], %mask, %passthru :
       ^

CC @lialan

[lialan]

@banach-space You can assign it to me, and I will take a look.