[Mlir-commits] [mlir] [mlir][SCF] Fix invalid IR in `ParallelOpSingleOrZeroIterationDimsFolder` pattern (PR #74552)

[Matthias Springer]

https://github.com/matthias-springer created https://github.com/llvm/llvm-project/pull/74552

`ParallelOpSingleOrZeroIterationDimsFolder` used to produce invalid IR:
```
within split at mlir/test/Dialect/SCF/canonicalize.mlir:1 offset :11:3: error: 'scf.parallel' op expects region #0 to have 0 or 1 blocks
  scf.parallel (%i0, %i1, %i2) = (%c0, %c3, %c7) to (%c1, %c6, %c10) step (%c1, %c2, %c3) {
  ^
within split at mlir/test/Dialect/SCF/canonicalize.mlir:1 offset :11:3: note: see current operation:
"scf.parallel"(%4, %5, %3) <{operandSegmentSizes = array<i32: 1, 1, 1, 0>}> ({
^bb0(%arg1: index):
  "memref.store"(%0, %arg0, %1, %arg1, %6) : (i32, memref<?x?x?xi32>, index, index, index) -> ()
  "scf.yield"() : () -> ()
^bb1(%8: index):  // no predecessors
  "scf.yield"() : () -> ()
}) : (index, index, index) -> ()
```

Together with #74551, this commit fixes `mlir/test/Dialect/SCF/canonicalize.mlir` when verifying the IR after each pattern application (#74270).

>From 103934a9a6b249241335d2bdea4afc868af5494b Mon Sep 17 00:00:00 2001
From: Matthias Springer <springerm at google.com>
Date: Wed, 6 Dec 2023 12:42:33 +0900
Subject: [PATCH] [mlir][SCF] Fix invalid IR in
 `ParallelOpSingleOrZeroIterationDimsFolder` pattern

`ParallelOpSingleOrZeroIterationDimsFolder` used to produce invalid IR:
```
within split at mlir/test/Dialect/SCF/canonicalize.mlir:1 offset :11:3: error: 'scf.parallel' op expects region #0 to have 0 or 1 blocks
  scf.parallel (%i0, %i1, %i2) = (%c0, %c3, %c7) to (%c1, %c6, %c10) step (%c1, %c2, %c3) {
  ^
within split at mlir/test/Dialect/SCF/canonicalize.mlir:1 offset :11:3: note: see current operation:
"scf.parallel"(%4, %5, %3) <{operandSegmentSizes = array<i32: 1, 1, 1, 0>}> ({
^bb0(%arg1: index):
  "memref.store"(%0, %arg0, %1, %arg1, %6) : (i32, memref<?x?x?xi32>, index, index, index) -> ()
  "scf.yield"() : () -> ()
^bb1(%8: index):  // no predecessors
  "scf.yield"() : () -> ()
}) : (index, index, index) -> ()
```

Together with #74551, this commit fixes `mlir/test/Dialect/SCF/canonicalize.mlir` when verifying the IR after each pattern application (#74270).
---
 mlir/lib/Dialect/SCF/IR/SCF.cpp | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mlir/lib/Dialect/SCF/IR/SCF.cpp b/mlir/lib/Dialect/SCF/IR/SCF.cpp
index 3b55704c4ea07..2e7382160f8eb 100644
--- a/mlir/lib/Dialect/SCF/IR/SCF.cpp
+++ b/mlir/lib/Dialect/SCF/IR/SCF.cpp
@@ -3040,6 +3040,8 @@ struct ParallelOpSingleOrZeroIterationDimsFolder
     auto newOp =
         rewriter.create<ParallelOp>(op.getLoc(), newLowerBounds, newUpperBounds,
                                     newSteps, op.getInitVals(), nullptr);
+    // Erase the empty block that was inserted by the builder.
+    rewriter.eraseBlock(newOp.getBody());
     // Clone the loop body and remap the block arguments of the collapsed loops
     // (inlining does not support a cancellable block argument mapping).
     rewriter.cloneRegionBefore(op.getRegion(), newOp.getRegion(),