[MLIR][Vector]Add constraints to vector.shape_cast(constant) -> constant

[MengmSun]

We have the case that after ConvertToLLVMPass it looks like:

...
%4 = llvm.mlir.constant(dense<0.000000e+00> : vector<192xf8E4M3FN>) : vector<192xi8>
%8 = vector.shape_cast %4 : vector<192xi8> to vector<1x192xi8>
%10 = vector.extract %8[0] : vector<192xi8> from vector<1x192xi8>
...

Our next pass is Canonicalizer. Several months ago everything went smoothly. However recently we met problem that

mlir::DenseElementsAttr mlir::DenseElementsAttr::reshape(mlir::ShapedType): Assertion `newType.getElementType() == curType.getElementType() && "expected the same element type"' failed.

and we found that's because a reshape operation is added for vector.shape_cast(constant) -> constant when calling ShapeCastOp::fold() in the Canonicalizer pass. This operation will fail if the element type of the source attribute and return type are different.

So we want to add the constraints that only when the element type of the source attribute and return type are the same it will return reshape operation to make our case work as before and will not influence other cases.

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[llvmbot]

@llvm/pr-subscribers-mlir-vector

@llvm/pr-subscribers-mlir

Author: Mengmeng Sun (MengmSun)

Changes

We have the case that after ConvertToLLVMPass it looks like:

...
%4 = llvm.mlir.constant(dense<0.000000e+00> : vector<192xf8E4M3FN>) : vector<192xi8>
%8 = vector.shape_cast %4 : vector<192xi8> to vector<1x192xi8>
%10 = vector.extract %8[0] : vector<192xi8> from vector<1x192xi8>
...

Our next pass is Canonicalizer. Several months ago everything went smoothly. However recently we met problem that

mlir::DenseElementsAttr mlir::DenseElementsAttr::reshape(mlir::ShapedType): Assertion `newType.getElementType() == curType.getElementType() && "expected the same element type"' failed.

and we found that's because a reshape operation is added for vector.shape_cast(constant) -> constant. This operation will fail if the element type of the source attribute and return type are different.

So we want to add the constraints that only when the element type of the source attribute and return type are the same it will return reshape operation to make our case work as before and will not influence other cases.

---

Full diff: https://github.com/llvm/llvm-project/pull/147691.diff

2 Files Affected:

• (modified) mlir/lib/Dialect/Vector/IR/VectorOps.cpp (+6-3)
• (modified) mlir/test/Dialect/Vector/canonicalize.mlir (+12)

diff --git a/mlir/lib/Dialect/Vector/IR/VectorOps.cpp b/mlir/lib/Dialect/Vector/IR/VectorOps.cpp
index 214d2ba7e1b8e..5bbe6704aac48 100644
--- a/mlir/lib/Dialect/Vector/IR/VectorOps.cpp
+++ b/mlir/lib/Dialect/Vector/IR/VectorOps.cpp
@@ -5922,10 +5922,13 @@ OpFoldResult ShapeCastOp::fold(FoldAdaptor adaptor) {
       return bcastOp.getSource();
   }
 
-  // shape_cast(constant) -> constant
+  // shape_cast(constant) -> constant,
+  // if element type of the source and result are the same
   if (auto splatAttr =
-          llvm::dyn_cast_if_present<SplatElementsAttr>(adaptor.getSource()))
-    return splatAttr.reshape(getType());
+          llvm::dyn_cast_if_present<SplatElementsAttr>(adaptor.getSource())) {
+    if (splatAttr.getElementType() == resultType.getElementType())
+      return splatAttr.reshape(getType());
+  }
 
   // shape_cast(poison) -> poison
   if (llvm::dyn_cast_if_present<ub::PoisonAttr>(adaptor.getSource())) {
diff --git a/mlir/test/Dialect/Vector/canonicalize.mlir b/mlir/test/Dialect/Vector/canonicalize.mlir
index 8a9e27378df61..69da8a31d2c9b 100644
--- a/mlir/test/Dialect/Vector/canonicalize.mlir
+++ b/mlir/test/Dialect/Vector/canonicalize.mlir
@@ -1002,6 +1002,18 @@ func.func @fold_broadcast_shapecast(%arg0: vector<4xf32>) -> vector<4xf32> {
 
 // -----
 
+// CHECK-LABEL: func @canonicalize_extract_shapecast_different_element_type
+func.func @canonicalize_extract_shapecast_different_element_type()->vector<12xi8> {
+  %0 = llvm.mlir.constant(dense<0.000000e+00> : vector<12xf8E4M3FN>) : vector<12xi8>
+  // CHECK-NOT: vector.shape_cast
+  %1 = vector.shape_cast %0 : vector<12xi8> to vector<1x12xi8>
+  // CHECK-NOT: vector.extract
+  %2 = vector.extract %1[0] : vector<12xi8> from vector<1x12xi8>
+  return %2 : vector<12xi8>
+}
+
+// -----
+
 // CHECK-LABEL: func @canonicalize_broadcast_shapecast_scalar
 //       CHECK:   vector.broadcast
 //   CHECK-NOT:   vector.shape_cast