Restore the initial ordering of dimensions before applying the pattern matching

Restore the initial ordering of dimensions before applying the pattern matching

Dimensions of band nodes can be implicitly permuted by the algorithm applied
during the schedule generation.

For example, in case of the following matrix-matrix multiplication,

for (i = 0; i < 1024; i++)
  for (k = 0; k < 1024; k++)
    for (j = 0; j < 1024; j++)
      C[i][j] += A[i][k] * B[k][j];

it can produce the following schedule tree

domain: "{ Stmt_for_body6[i0, i1, i2] : 0 <= i0 <= 1023 and 0 <= i1 <= 1023 and
                                        0 <= i2 <= 1023 }"
child:
  schedule: "[{ Stmt_for_body6[i0, i1, i2] -> [(i0)] },
              { Stmt_for_body6[i0, i1, i2] -> [(i1)] },
              { Stmt_for_body6[i0, i1, i2] -> [(i2)] }]"
  permutable: 1
  coincident: [ 1, 1, 0 ]

The current implementation of the pattern matching optimizations relies on the
initial ordering of dimensions. Otherwise, it can produce the miscompilation
(e.g., [1]).

This patch helps to restore the initial ordering of dimensions by recreating
the band node when the corresponding conditions are satisfied.

Refs.:

[1] - https://bugs.llvm.org/show_bug.cgi?id=32500

Reviewed-by: Michael Kruse <llvm@meinersbur.de>
Differential Revision: https://reviews.llvm.org/D31741

llvm-svn: 299662