[Mlir-commits] [mlir] [mlir][Linalg]: Add rewrite pattern to fuse fill with reduce operations (PR #125401)

[Kunwar Grover]

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@@ -1893,6 +1893,34 @@ void populateDecomposeWinogradOpsPatterns(RewritePatternSet &patterns);
 /// convert to a `linalg.dot`.
 void populateContractionOpRankReducingPatterns(RewritePatternSet &patterns);
 
+/// Add patterns to fuse a linalg fill operation with a linalg operation.
+/// Add patterns to fold linalg.fill into linalg.reduce by creating a fused
+/// linalg.generic operation.
+/// The fill operation is expected to happen only on the first index
+/// of the reduction dimension. Currently only one reduction dimension is
+/// supported. Given the pattern:
+///   %empty = tensor.empty() : tensor<i8>
+///   %filled = linalg.fill ins(%c0 : i8) outs(%empty : tensor<i8>) ->
+///   tensor<i8> %reduced = linalg.reduce ins(%0 : tensor<147456xi8>)
+///   outs(%filled : tensor<i8>) dimensions = [0]
+///     (%in: i8, %init: i8) {
+///       %3 = arith.addi %in, %init : i8
+///       linalg.yield %3 : i8
+///   }
+/// The pattern is rewritten into:
+///   %empty = tensor.empty() : tensor<i8>
+///   %reduced = linalg.generic ins(%0 : tensor<147456xi8>) outs(%empty :
+///   tensor<i8>) {
+///     ^bb0(%in: i8, %init: i8):
+///       %cst = arith.constant 0 : index
+///       %index = linalg.index %c0 : index
+///       %cmp = arith.cmpi eq, %cst, %index : i1
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Groverkss wrote:

The iteration order of reduction and parallel iterators in a linalg operation is undefined. I don't think you can assume that the first iteration of the iterator is 0.

https://github.com/llvm/llvm-project/pull/125401