[Mlir-commits] [mlir] [mlir][vector] Fix a `target-rank=0` unrolling (PR #73365)

[Rik Huijzer]

https://github.com/rikhuijzer created https://github.com/llvm/llvm-project/pull/73365

Fixes https://github.com/llvm/llvm-project/issues/64269.

I've also tried to proactively find other `target-rank=0` bugs, but couldn't find any. `options.targetRank` is only used 8 times throughout the `mlir` folder, all inside `VectorToSCF.cpp`. None of the other uses look like they could cause a crash. I've also tried

```mlir
func.func @main(%vec : vector<2xi32>) -> vector<2xi32> {
  %alloc = memref.alloc() : memref<4xindex>
  %c0 = arith.constant 0 : index
  %out = vector.transfer_read %alloc[%c0], %c0 : memref<4xindex>, vector<2xi32>
  return %out : vector<2xi32>
}
```
with `"--convert-vector-to-scf=full-unroll target-rank=0"` and that also didn't crash. (Maybe obvious. I have to admit that I'm not very familiar with these ops.)

>From 74c6b927c77b50042817dc7f46dccbc1995c721c Mon Sep 17 00:00:00 2001
From: Rik Huijzer <github at huijzer.xyz>
Date: Fri, 24 Nov 2023 20:55:10 +0100
Subject: [PATCH 1/2] [mlir][vector] Fix a `target-rank=0` unrolling

---
 mlir/lib/Conversion/VectorToSCF/VectorToSCF.cpp | 17 ++++++++++++-----
 .../Conversion/VectorToSCF/vector-to-scf.mlir   | 14 ++++++++++++++
 2 files changed, 26 insertions(+), 5 deletions(-)

diff --git a/mlir/lib/Conversion/VectorToSCF/VectorToSCF.cpp b/mlir/lib/Conversion/VectorToSCF/VectorToSCF.cpp
index 6ba3a678b2da7eb..1483c88cc614a86 100644
--- a/mlir/lib/Conversion/VectorToSCF/VectorToSCF.cpp
+++ b/mlir/lib/Conversion/VectorToSCF/VectorToSCF.cpp
@@ -1207,23 +1207,30 @@ struct UnrollTransferWriteConversion
   /// accesses, and broadcasts and transposes in permutation maps.
   LogicalResult matchAndRewrite(TransferWriteOp xferOp,
                                 PatternRewriter &rewriter) const override {
-    if (xferOp.getVectorType().getRank() <= options.targetRank)
+    VectorType inputVectorTy = xferOp.getVectorType();
+
+    if (inputVectorTy.getRank() <= options.targetRank)
       return failure();
+
+    // When target-rank=0, unrolling would cause the vector input argument
+    // into `transfer_write` to become a scalar.
+    if (inputVectorTy.getRank() == 1)
+      return failure();
+
     if (isTensorOp(xferOp) && !options.lowerTensors)
       return failure();
     // Transfer ops that modify the element type are not supported atm.
-    if (xferOp.getVectorType().getElementType() !=
+    if (inputVectorTy.getElementType() !=
         xferOp.getShapedType().getElementType())
       return failure();
 
     auto vec = getDataVector(xferOp);
-    auto xferVecType = xferOp.getVectorType();
-    if (xferVecType.getScalableDims()[0]) {
+    if (inputVectorTy.getScalableDims()[0]) {
       // Cannot unroll a scalable dimension at compile time.
       return failure();
     }
 
-    int64_t dimSize = xferVecType.getShape()[0];
+    int64_t dimSize = inputVectorTy.getShape()[0];
     Value source = xferOp.getSource(); // memref or tensor to be written to.
     auto sourceType = isTensorOp(xferOp) ? xferOp.getShapedType() : Type();
 
diff --git a/mlir/test/Conversion/VectorToSCF/vector-to-scf.mlir b/mlir/test/Conversion/VectorToSCF/vector-to-scf.mlir
index 597cc4f71a63961..318c6583c15af56 100644
--- a/mlir/test/Conversion/VectorToSCF/vector-to-scf.mlir
+++ b/mlir/test/Conversion/VectorToSCF/vector-to-scf.mlir
@@ -1,5 +1,6 @@
 // RUN: mlir-opt %s -pass-pipeline="builtin.module(func.func(convert-vector-to-scf))" -split-input-file -allow-unregistered-dialect | FileCheck %s
 // RUN: mlir-opt %s -pass-pipeline="builtin.module(func.func(convert-vector-to-scf{full-unroll=true}))" -split-input-file -allow-unregistered-dialect | FileCheck %s --check-prefix=FULL-UNROLL
+// RUN: mlir-opt %s "-convert-vector-to-scf=full-unroll target-rank=0" -split-input-file -allow-unregistered-dialect | FileCheck %s --check-prefix=TARGET-RANK-ZERO
 
 // CHECK-LABEL: func @vector_transfer_ops_0d(
 func.func @vector_transfer_ops_0d(%M: memref<f32>) {
@@ -748,3 +749,16 @@ func.func @cannot_fully_unroll_transfer_write_of_nd_scalable_vector(%vec: vector
   vector.transfer_write %vec, %memref[%c0, %c0] {in_bounds = [true, true]} : vector<[4]x[4]xf32>, memref<?x?xf32>
   return
 }
+
+//  -----
+
+// TARGET-RANK-ZERO-LABEL: func @cannot_further_unroll_transfer_write
+func.func @cannot_further_unroll_transfer_write(%vec : vector<2xi32>) {
+  // FULL-UNROLL-NOT: vector.extract
+  // FULL-UNROLL: vector.transfer_write
+  // FULL-UNROLL-NOT: vector.extract
+  %alloc = memref.alloc() : memref<4xi32>
+  %c0 = arith.constant 0 : index
+  vector.transfer_write %vec, %alloc[%c0] : vector<2xi32>, memref<4xi32>
+  return
+}

>From 7dba76e5bb8800bd08922e2b54bac14e808046c5 Mon Sep 17 00:00:00 2001
From: Rik Huijzer <github at huijzer.xyz>
Date: Fri, 24 Nov 2023 21:17:32 +0100
Subject: [PATCH 2/2] Fix label in test

---
 mlir/test/Conversion/VectorToSCF/vector-to-scf.mlir | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mlir/test/Conversion/VectorToSCF/vector-to-scf.mlir b/mlir/test/Conversion/VectorToSCF/vector-to-scf.mlir
index 318c6583c15af56..d5b02006dbd12fb 100644
--- a/mlir/test/Conversion/VectorToSCF/vector-to-scf.mlir
+++ b/mlir/test/Conversion/VectorToSCF/vector-to-scf.mlir
@@ -754,9 +754,9 @@ func.func @cannot_fully_unroll_transfer_write_of_nd_scalable_vector(%vec: vector
 
 // TARGET-RANK-ZERO-LABEL: func @cannot_further_unroll_transfer_write
 func.func @cannot_further_unroll_transfer_write(%vec : vector<2xi32>) {
-  // FULL-UNROLL-NOT: vector.extract
-  // FULL-UNROLL: vector.transfer_write
-  // FULL-UNROLL-NOT: vector.extract
+  // TARGET-RANK-ZERO-NOT: vector.extract
+  // TARGET-RANK-ZERO: vector.transfer_write
+  // TARGET-RANK-ZERO-NOT: vector.extract
   %alloc = memref.alloc() : memref<4xi32>
   %c0 = arith.constant 0 : index
   vector.transfer_write %vec, %alloc[%c0] : vector<2xi32>, memref<4xi32>