[Mlir-commits] [mlir] [mli][vector] canonicalize vector.from_elements from ascending extracts (PR #139819)

James Newling llvmlistbot at llvm.org
Wed May 14 12:40:02 PDT 2025


https://github.com/newling updated https://github.com/llvm/llvm-project/pull/139819

>From c252a3dd92ab1145dc80a847729423366a8f1dea Mon Sep 17 00:00:00 2001
From: James Newling <james.newling at gmail.com>
Date: Tue, 13 May 2025 16:06:45 -0700
Subject: [PATCH 1/5] first commit

---
 mlir/lib/Dialect/Vector/IR/VectorOps.cpp      | 58 +++++++++++++++
 mlir/test/Dialect/Vector/canonicalize.mlir    | 69 ------------------
 .../canonicalize/vector-from-elements.mlir    | 72 +++++++++++++++++++
 3 files changed, 130 insertions(+), 69 deletions(-)
 create mode 100644 mlir/test/Dialect/Vector/canonicalize/vector-from-elements.mlir

diff --git a/mlir/lib/Dialect/Vector/IR/VectorOps.cpp b/mlir/lib/Dialect/Vector/IR/VectorOps.cpp
index f6c3c6a61afb6..71844e62baba7 100644
--- a/mlir/lib/Dialect/Vector/IR/VectorOps.cpp
+++ b/mlir/lib/Dialect/Vector/IR/VectorOps.cpp
@@ -2385,6 +2385,64 @@ static LogicalResult rewriteFromElementsAsSplat(FromElementsOp fromElementsOp,
   return success();
 }
 
+static LogicalResult
+rewriteFromElementsAsShapeCast(FromElementsOp fromElementsOp,
+                               PatternRewriter &rewriter) {
+
+  mlir::OperandRange elements = fromElementsOp.getElements();
+  const size_t nbElements = elements.size();
+  assert(nbElements > 0 && "must be at least one element");
+
+  // https://en.wikipedia.org/wiki/List_of_prime_numbers
+  const int prime = 5387;
+  bool pseudoRandomOrder = nbElements < prime;
+
+  Value source;
+  ArrayRef<int64_t> shape;
+  for (size_t elementIndex = 0ULL; elementIndex < nbElements; elementIndex++) {
+
+    // Rather than iterating through the elements in ascending order, we might
+    // be able to exit quickly if we go through in pseudo-random order. Use
+    // fact that (i * p) % a is a bijection for i in [0, a) if p is prime and
+    // a < p.
+    int currentIndex =
+        pseudoRandomOrder ? elementIndex : (elementIndex * prime) % nbElements;
+    Value element = elements[currentIndex];
+
+    // From an extract on the same source as the other elements.
+    auto extractOp =
+        dyn_cast_if_present<vector::ExtractOp>(element.getDefiningOp());
+    if (!extractOp)
+      return failure();
+    Value currentSource = extractOp.getVector();
+    if (!source) {
+      source = currentSource;
+      shape = extractOp.getSourceVectorType().getShape();
+    } else if (currentSource != source) {
+      return failure();
+    }
+
+    ArrayRef<int64_t> position = extractOp.getStaticPosition();
+    assert(position.size() == shape.size());
+
+    int64_t stride{1};
+    int64_t offset{0};
+    for (auto [pos, size] :
+         llvm::zip(llvm::reverse(position), llvm::reverse(shape))) {
+      if (pos == ShapedType::kDynamic)
+        return failure();
+      offset += pos * stride;
+      stride *= size;
+    }
+    if (offset != currentIndex)
+      return failure();
+  }
+
+  // Can replace with a shape_cast.
+  rewriter.replaceOpWithNewOp<ShapeCastOp>(fromElementsOp,
+                                           fromElementsOp.getType(), source);
+}
+
 void FromElementsOp::getCanonicalizationPatterns(RewritePatternSet &results,
                                                  MLIRContext *context) {
   results.add(rewriteFromElementsAsSplat);
diff --git a/mlir/test/Dialect/Vector/canonicalize.mlir b/mlir/test/Dialect/Vector/canonicalize.mlir
index 99f0850000a16..6af517d988360 100644
--- a/mlir/test/Dialect/Vector/canonicalize.mlir
+++ b/mlir/test/Dialect/Vector/canonicalize.mlir
@@ -2952,75 +2952,6 @@ func.func @extract_from_0d_splat_broadcast_regression(%a: f32, %b: vector<f32>,
 
 // -----
 
-// CHECK-LABEL: func @extract_scalar_from_from_elements(
-//  CHECK-SAME:     %[[a:.*]]: f32, %[[b:.*]]: f32)
-func.func @extract_scalar_from_from_elements(%a: f32, %b: f32) -> (f32, f32, f32, f32, f32, f32, f32) {
-  // Extract from 0D.
-  %0 = vector.from_elements %a : vector<f32>
-  %1 = vector.extract %0[] : f32 from vector<f32>
-
-  // Extract from 1D.
-  %2 = vector.from_elements %a : vector<1xf32>
-  %3 = vector.extract %2[0] : f32 from vector<1xf32>
-  %4 = vector.from_elements %a, %b, %a, %a, %b : vector<5xf32>
-  %5 = vector.extract %4[4] : f32 from vector<5xf32>
-
-  // Extract from 2D.
-  %6 = vector.from_elements %a, %a, %a, %b, %b, %b : vector<2x3xf32>
-  %7 = vector.extract %6[0, 0] : f32 from vector<2x3xf32>
-  %8 = vector.extract %6[0, 1] : f32 from vector<2x3xf32>
-  %9 = vector.extract %6[1, 1] : f32 from vector<2x3xf32>
-  %10 = vector.extract %6[1, 2] : f32 from vector<2x3xf32>
-
-  // CHECK: return %[[a]], %[[a]], %[[b]], %[[a]], %[[a]], %[[b]], %[[b]]
-  return %1, %3, %5, %7, %8, %9, %10 : f32, f32, f32, f32, f32, f32, f32
-}
-
-// -----
-
-// CHECK-LABEL: func @extract_1d_from_from_elements(
-//  CHECK-SAME:     %[[a:.*]]: f32, %[[b:.*]]: f32)
-func.func @extract_1d_from_from_elements(%a: f32, %b: f32) -> (vector<3xf32>, vector<3xf32>) {
-  %0 = vector.from_elements %a, %a, %a, %b, %b, %b : vector<2x3xf32>
-  // CHECK: %[[splat1:.*]] = vector.splat %[[a]] : vector<3xf32>
-  %1 = vector.extract %0[0] : vector<3xf32> from vector<2x3xf32>
-  // CHECK: %[[splat2:.*]] = vector.splat %[[b]] : vector<3xf32>
-  %2 = vector.extract %0[1] : vector<3xf32> from vector<2x3xf32>
-  // CHECK: return %[[splat1]], %[[splat2]]
-  return %1, %2 : vector<3xf32>, vector<3xf32>
-}
-
-// -----
-
-// CHECK-LABEL: func @extract_2d_from_from_elements(
-//  CHECK-SAME:     %[[a:.*]]: f32, %[[b:.*]]: f32)
-func.func @extract_2d_from_from_elements(%a: f32, %b: f32) -> (vector<2x2xf32>, vector<2x2xf32>) {
-  %0 = vector.from_elements %a, %a, %a, %b, %b, %b, %b, %a, %b, %a, %a, %b : vector<3x2x2xf32>
-  // CHECK: %[[splat1:.*]] = vector.from_elements %[[a]], %[[a]], %[[a]], %[[b]] : vector<2x2xf32>
-  %1 = vector.extract %0[0] : vector<2x2xf32> from vector<3x2x2xf32>
-  // CHECK: %[[splat2:.*]] = vector.from_elements %[[b]], %[[b]], %[[b]], %[[a]] : vector<2x2xf32>
-  %2 = vector.extract %0[1] : vector<2x2xf32> from vector<3x2x2xf32>
-  // CHECK: return %[[splat1]], %[[splat2]]
-  return %1, %2 : vector<2x2xf32>, vector<2x2xf32>
-}
-
-// -----
-
-// CHECK-LABEL: func @from_elements_to_splat(
-//  CHECK-SAME:     %[[a:.*]]: f32, %[[b:.*]]: f32)
-func.func @from_elements_to_splat(%a: f32, %b: f32) -> (vector<2x3xf32>, vector<2x3xf32>, vector<f32>) {
-  // CHECK: %[[splat:.*]] = vector.splat %[[a]] : vector<2x3xf32>
-  %0 = vector.from_elements %a, %a, %a, %a, %a, %a : vector<2x3xf32>
-  // CHECK: %[[from_el:.*]] = vector.from_elements {{.*}} : vector<2x3xf32>
-  %1 = vector.from_elements %a, %a, %a, %a, %b, %a : vector<2x3xf32>
-  // CHECK: %[[splat2:.*]] = vector.splat %[[a]] : vector<f32>
-  %2 = vector.from_elements %a : vector<f32>
-  // CHECK: return %[[splat]], %[[from_el]], %[[splat2]]
-  return %0, %1, %2 : vector<2x3xf32>, vector<2x3xf32>, vector<f32>
-}
-
-// -----
-
 // CHECK-LABEL: func @vector_insert_const_regression(
 //       CHECK:   llvm.mlir.undef
 //       CHECK:   vector.insert
diff --git a/mlir/test/Dialect/Vector/canonicalize/vector-from-elements.mlir b/mlir/test/Dialect/Vector/canonicalize/vector-from-elements.mlir
new file mode 100644
index 0000000000000..21ce71473a3cd
--- /dev/null
+++ b/mlir/test/Dialect/Vector/canonicalize/vector-from-elements.mlir
@@ -0,0 +1,72 @@
+// RUN: mlir-opt %s -canonicalize="test-convergence" -split-input-file -allow-unregistered-dialect | FileCheck %s
+
+// This file contains some tests of folding/canonicalizing vector.from_elements 
+
+// CHECK-LABEL: func @extract_scalar_from_from_elements(
+//  CHECK-SAME:     %[[a:.*]]: f32, %[[b:.*]]: f32)
+func.func @extract_scalar_from_from_elements(%a: f32, %b: f32) -> (f32, f32, f32, f32, f32, f32, f32) {
+  // Extract from 0D.
+  %0 = vector.from_elements %a : vector<f32>
+  %1 = vector.extract %0[] : f32 from vector<f32>
+
+  // Extract from 1D.
+  %2 = vector.from_elements %a : vector<1xf32>
+  %3 = vector.extract %2[0] : f32 from vector<1xf32>
+  %4 = vector.from_elements %a, %b, %a, %a, %b : vector<5xf32>
+  %5 = vector.extract %4[4] : f32 from vector<5xf32>
+
+  // Extract from 2D.
+  %6 = vector.from_elements %a, %a, %a, %b, %b, %b : vector<2x3xf32>
+  %7 = vector.extract %6[0, 0] : f32 from vector<2x3xf32>
+  %8 = vector.extract %6[0, 1] : f32 from vector<2x3xf32>
+  %9 = vector.extract %6[1, 1] : f32 from vector<2x3xf32>
+  %10 = vector.extract %6[1, 2] : f32 from vector<2x3xf32>
+
+  // CHECK: return %[[a]], %[[a]], %[[b]], %[[a]], %[[a]], %[[b]], %[[b]]
+  return %1, %3, %5, %7, %8, %9, %10 : f32, f32, f32, f32, f32, f32, f32
+}
+
+// -----
+
+// CHECK-LABEL: func @extract_1d_from_from_elements(
+//  CHECK-SAME:     %[[a:.*]]: f32, %[[b:.*]]: f32)
+func.func @extract_1d_from_from_elements(%a: f32, %b: f32) -> (vector<3xf32>, vector<3xf32>) {
+  %0 = vector.from_elements %a, %a, %a, %b, %b, %b : vector<2x3xf32>
+  // CHECK: %[[splat1:.*]] = vector.splat %[[a]] : vector<3xf32>
+  %1 = vector.extract %0[0] : vector<3xf32> from vector<2x3xf32>
+  // CHECK: %[[splat2:.*]] = vector.splat %[[b]] : vector<3xf32>
+  %2 = vector.extract %0[1] : vector<3xf32> from vector<2x3xf32>
+  // CHECK: return %[[splat1]], %[[splat2]]
+  return %1, %2 : vector<3xf32>, vector<3xf32>
+}
+
+// -----
+
+// CHECK-LABEL: func @extract_2d_from_from_elements(
+//  CHECK-SAME:     %[[a:.*]]: f32, %[[b:.*]]: f32)
+func.func @extract_2d_from_from_elements(%a: f32, %b: f32) -> (vector<2x2xf32>, vector<2x2xf32>) {
+  %0 = vector.from_elements %a, %a, %a, %b, %b, %b, %b, %a, %b, %a, %a, %b : vector<3x2x2xf32>
+  // CHECK: %[[splat1:.*]] = vector.from_elements %[[a]], %[[a]], %[[a]], %[[b]] : vector<2x2xf32>
+  %1 = vector.extract %0[0] : vector<2x2xf32> from vector<3x2x2xf32>
+  // CHECK: %[[splat2:.*]] = vector.from_elements %[[b]], %[[b]], %[[b]], %[[a]] : vector<2x2xf32>
+  %2 = vector.extract %0[1] : vector<2x2xf32> from vector<3x2x2xf32>
+  // CHECK: return %[[splat1]], %[[splat2]]
+  return %1, %2 : vector<2x2xf32>, vector<2x2xf32>
+}
+
+// -----
+
+// CHECK-LABEL: func @from_elements_to_splat(
+//  CHECK-SAME:     %[[a:.*]]: f32, %[[b:.*]]: f32)
+func.func @from_elements_to_splat(%a: f32, %b: f32) -> (vector<2x3xf32>, vector<2x3xf32>, vector<f32>) {
+  // CHECK: %[[splat:.*]] = vector.splat %[[a]] : vector<2x3xf32>
+  %0 = vector.from_elements %a, %a, %a, %a, %a, %a : vector<2x3xf32>
+  // CHECK: %[[from_el:.*]] = vector.from_elements {{.*}} : vector<2x3xf32>
+  %1 = vector.from_elements %a, %a, %a, %a, %b, %a : vector<2x3xf32>
+  // CHECK: %[[splat2:.*]] = vector.splat %[[a]] : vector<f32>
+  %2 = vector.from_elements %a : vector<f32>
+  // CHECK: return %[[splat]], %[[from_el]], %[[splat2]]
+  return %0, %1, %2 : vector<2x3xf32>, vector<2x3xf32>, vector<f32>
+}
+
+// -----

>From 7f40da6728bb5b197548d3466818869d45ce9720 Mon Sep 17 00:00:00 2001
From: James Newling <james.newling at gmail.com>
Date: Tue, 13 May 2025 17:33:41 -0700
Subject: [PATCH 2/5] improvements

---
 mlir/lib/Dialect/Vector/IR/VectorOps.cpp      | 46 ++++++------
 .../canonicalize/vector-from-elements.mlir    | 73 +++++++++++++++++++
 2 files changed, 98 insertions(+), 21 deletions(-)

diff --git a/mlir/lib/Dialect/Vector/IR/VectorOps.cpp b/mlir/lib/Dialect/Vector/IR/VectorOps.cpp
index 71844e62baba7..e0ce41e5d6245 100644
--- a/mlir/lib/Dialect/Vector/IR/VectorOps.cpp
+++ b/mlir/lib/Dialect/Vector/IR/VectorOps.cpp
@@ -2385,45 +2385,49 @@ static LogicalResult rewriteFromElementsAsSplat(FromElementsOp fromElementsOp,
   return success();
 }
 
+
+/// Rewrite a vecor.from_elements as a vector.shape_cast, if possible. 
+///
+/// Example:
+///   %0 = vector.extract %source[0, 0] : i8 from vector<1x2xi8>
+///   %1 = vector.extract %source[0, 1] : i8 from vector<1x2xi8>
+///   %2 = vector.from_elements %0, %1 : vector<2xi8>
+///
+/// becomes
+///   %2 = vector.shape_cast %source : vector<1x2xi8> to vector<2xi8>
 static LogicalResult
 rewriteFromElementsAsShapeCast(FromElementsOp fromElementsOp,
                                PatternRewriter &rewriter) {
 
-  mlir::OperandRange elements = fromElementsOp.getElements();
-  const size_t nbElements = elements.size();
-  assert(nbElements > 0 && "must be at least one element");
-
-  // https://en.wikipedia.org/wiki/List_of_prime_numbers
-  const int prime = 5387;
-  bool pseudoRandomOrder = nbElements < prime;
-
+  // The common source of vector.extract operations (if one exists), as well
+  // as its shape and rank. Set in the first iteration of the loop over the
+  // operands of `fromElementsOp`.
   Value source;
   ArrayRef<int64_t> shape;
-  for (size_t elementIndex = 0ULL; elementIndex < nbElements; elementIndex++) {
+  int64_t rank;
 
-    // Rather than iterating through the elements in ascending order, we might
-    // be able to exit quickly if we go through in pseudo-random order. Use
-    // fact that (i * p) % a is a bijection for i in [0, a) if p is prime and
-    // a < p.
-    int currentIndex =
-        pseudoRandomOrder ? elementIndex : (elementIndex * prime) % nbElements;
-    Value element = elements[currentIndex];
+  for (auto [index, element] : llvm::enumerate(fromElementsOp.getElements())) {
 
-    // From an extract on the same source as the other elements.
+    // Check that the element is defined by an extract operation, and that
+    // the extract is on the same vector as all preceding elements.
     auto extractOp =
         dyn_cast_if_present<vector::ExtractOp>(element.getDefiningOp());
     if (!extractOp)
       return failure();
     Value currentSource = extractOp.getVector();
-    if (!source) {
+    if (index == 0) {
       source = currentSource;
       shape = extractOp.getSourceVectorType().getShape();
+      rank = shape.size();
     } else if (currentSource != source) {
       return failure();
     }
 
+    // Check that the (linearized) index of extraction is the same as the index
+    // in the result of `fromElementsOp`.
     ArrayRef<int64_t> position = extractOp.getStaticPosition();
-    assert(position.size() == shape.size());
+    if (position.size() != rank)
+      return failure();
 
     int64_t stride{1};
     int64_t offset{0};
@@ -2434,11 +2438,10 @@ rewriteFromElementsAsShapeCast(FromElementsOp fromElementsOp,
       offset += pos * stride;
       stride *= size;
     }
-    if (offset != currentIndex)
+    if (offset != index)
       return failure();
   }
 
-  // Can replace with a shape_cast.
   rewriter.replaceOpWithNewOp<ShapeCastOp>(fromElementsOp,
                                            fromElementsOp.getType(), source);
 }
@@ -2446,6 +2449,7 @@ rewriteFromElementsAsShapeCast(FromElementsOp fromElementsOp,
 void FromElementsOp::getCanonicalizationPatterns(RewritePatternSet &results,
                                                  MLIRContext *context) {
   results.add(rewriteFromElementsAsSplat);
+  results.add(rewriteFromElementsAsShapeCast);
 }
 
 //===----------------------------------------------------------------------===//
diff --git a/mlir/test/Dialect/Vector/canonicalize/vector-from-elements.mlir b/mlir/test/Dialect/Vector/canonicalize/vector-from-elements.mlir
index 21ce71473a3cd..fafac4419d719 100644
--- a/mlir/test/Dialect/Vector/canonicalize/vector-from-elements.mlir
+++ b/mlir/test/Dialect/Vector/canonicalize/vector-from-elements.mlir
@@ -2,6 +2,10 @@
 
 // This file contains some tests of folding/canonicalizing vector.from_elements 
 
+///===----------------------------------------------===//
+///  Tests of `rewriteFromElementsAsSplat`
+///===----------------------------------------------===//
+
 // CHECK-LABEL: func @extract_scalar_from_from_elements(
 //  CHECK-SAME:     %[[a:.*]]: f32, %[[b:.*]]: f32)
 func.func @extract_scalar_from_from_elements(%a: f32, %b: f32) -> (f32, f32, f32, f32, f32, f32, f32) {
@@ -70,3 +74,72 @@ func.func @from_elements_to_splat(%a: f32, %b: f32) -> (vector<2x3xf32>, vector<
 }
 
 // -----
+
+
+///===----------------------------------------------===//
+///  Tests of `rewriteFromElementsAsShapeCast`
+///===----------------------------------------------===//
+
+// CHECK-LABEL: func @to_shape_cast_rank2_to_rank1(
+//  CHECK-SAME:       %[[a:.*]]: vector<1x2xi8>)
+//       CHECK:       %[[shape_cast:.*]] = vector.shape_cast %[[a]] : vector<1x2xi8> to vector<2xi8>
+//       CHECK:       return %[[shape_cast]] : vector<2xi8>
+func.func @to_shape_cast_rank2_to_rank1(%arg0: vector<1x2xi8>) -> vector<2xi8> {
+  %0 = vector.extract %arg0[0, 0] : i8 from vector<1x2xi8>
+  %1 = vector.extract %arg0[0, 1] : i8 from vector<1x2xi8>
+  %4 = vector.from_elements %0, %1 : vector<2xi8>
+  return %4 : vector<2xi8>
+}
+
+// -----
+
+// CHECK-LABEL: func @to_shape_cast_rank1_to_rank3(
+//  CHECK-SAME:       %[[a:.*]]: vector<8xi8>)
+//       CHECK:       %[[shape_cast:.*]] = vector.shape_cast %[[a]] : vector<8xi8> to vector<2x2x2xi8>
+//       CHECK:       return %[[shape_cast]] : vector<2x2x2xi8>
+func.func @to_shape_cast_rank1_to_rank3(%arg0: vector<8xi8>) -> vector<2x2x2xi8> {
+  %0 = vector.extract %arg0[0] : i8 from vector<8xi8>
+  %1 = vector.extract %arg0[1] : i8 from vector<8xi8>
+  %2 = vector.extract %arg0[2] : i8 from vector<8xi8>
+  %3 = vector.extract %arg0[3] : i8 from vector<8xi8>
+  %4 = vector.extract %arg0[4] : i8 from vector<8xi8>
+  %5 = vector.extract %arg0[5] : i8 from vector<8xi8>
+  %6 = vector.extract %arg0[6] : i8 from vector<8xi8>
+  %7 = vector.extract %arg0[7] : i8 from vector<8xi8>
+  %8 = vector.from_elements %0, %1, %2, %3, %4, %5, %6, %7 : vector<2x2x2xi8>
+  return %8 : vector<2x2x2xi8>
+}
+
+// -----
+
+// The extracted elements are recombined into a single vector, but in a new order. 
+// CHECK-LABEL: func @negative_nonascending_order(
+//   CHECK-NOT: shape_cast
+func.func @negative_nonascending_order(%arg0: vector<1x2xi8>) -> vector<2xi8> {
+  %0 = vector.extract %arg0[0, 1] : i8 from vector<1x2xi8>
+  %1 = vector.extract %arg0[0, 0] : i8 from vector<1x2xi8>
+  %2 = vector.from_elements %0, %1 : vector<2xi8>
+  return %2 : vector<2xi8>
+}
+
+// ----- 
+
+// CHECK-LABEL: func @negative_nonstatic_extract(
+//   CHECK-NOT: shape_cast
+func.func @negative_nonstatic_extract(%arg0: vector<1x2xi8>, %i0 : index, %i1 : index) -> vector<2xi8> {
+  %0 = vector.extract %arg0[0, %i0] : i8 from vector<1x2xi8>
+  %1 = vector.extract %arg0[0, %i1] : i8 from vector<1x2xi8>
+  %2 = vector.from_elements %0, %1 : vector<2xi8>
+  return %2 : vector<2xi8>
+}
+
+// -----
+
+// CHECK-LABEL: func @negative_different_sources(
+//   CHECK-NOT: shape_cast
+func.func @negative_different_sources(%arg0: vector<1x2xi8>, %arg1: vector<1x2xi8>) -> vector<2xi8> {
+  %0 = vector.extract %arg0[0, 0] : i8 from vector<1x2xi8>
+  %1 = vector.extract %arg1[0, 1] : i8 from vector<1x2xi8>
+  %2 = vector.from_elements %0, %1 : vector<2xi8>
+  return %2 : vector<2xi8>
+}

>From 3ce0713d33fef03141239a00033f5bf5c896fc72 Mon Sep 17 00:00:00 2001
From: James Newling <james.newling at gmail.com>
Date: Tue, 13 May 2025 17:41:11 -0700
Subject: [PATCH 3/5] apply some polish

---
 mlir/lib/Dialect/Vector/IR/VectorOps.cpp | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/mlir/lib/Dialect/Vector/IR/VectorOps.cpp b/mlir/lib/Dialect/Vector/IR/VectorOps.cpp
index e0ce41e5d6245..e0b406ce0bc46 100644
--- a/mlir/lib/Dialect/Vector/IR/VectorOps.cpp
+++ b/mlir/lib/Dialect/Vector/IR/VectorOps.cpp
@@ -2385,8 +2385,7 @@ static LogicalResult rewriteFromElementsAsSplat(FromElementsOp fromElementsOp,
   return success();
 }
 
-
-/// Rewrite a vecor.from_elements as a vector.shape_cast, if possible. 
+/// Rewrite vector.from_elements as vector.shape_cast, if possible.
 ///
 /// Example:
 ///   %0 = vector.extract %source[0, 0] : i8 from vector<1x2xi8>
@@ -2400,8 +2399,8 @@ rewriteFromElementsAsShapeCast(FromElementsOp fromElementsOp,
                                PatternRewriter &rewriter) {
 
   // The common source of vector.extract operations (if one exists), as well
-  // as its shape and rank. Set in the first iteration of the loop over the
-  // operands of `fromElementsOp`.
+  // as its shape and rank. These are set in the first iteration of the loop
+  // over the operands (elements) of `fromElementsOp`.
   Value source;
   ArrayRef<int64_t> shape;
   int64_t rank;
@@ -2426,9 +2425,8 @@ rewriteFromElementsAsShapeCast(FromElementsOp fromElementsOp,
     // Check that the (linearized) index of extraction is the same as the index
     // in the result of `fromElementsOp`.
     ArrayRef<int64_t> position = extractOp.getStaticPosition();
-    if (position.size() != rank)
-      return failure();
-
+    assert(position.size() == rank &&
+           "scalar extract must have full rank position");
     int64_t stride{1};
     int64_t offset{0};
     for (auto [pos, size] :

>From 94c5d8c7b3919975f46437c481f9f49e076814f8 Mon Sep 17 00:00:00 2001
From: James Newling <james.newling at gmail.com>
Date: Wed, 14 May 2025 11:28:40 -0700
Subject: [PATCH 4/5] fix blindspot where source is larger

---
 mlir/lib/Dialect/Vector/IR/VectorOps.cpp      | 116 +++++++++++-------
 .../canonicalize/vector-from-elements.mlir    |  11 ++
 2 files changed, 84 insertions(+), 43 deletions(-)

diff --git a/mlir/lib/Dialect/Vector/IR/VectorOps.cpp b/mlir/lib/Dialect/Vector/IR/VectorOps.cpp
index e0b406ce0bc46..7b7f014480ccd 100644
--- a/mlir/lib/Dialect/Vector/IR/VectorOps.cpp
+++ b/mlir/lib/Dialect/Vector/IR/VectorOps.cpp
@@ -33,6 +33,7 @@
 #include "mlir/IR/OpImplementation.h"
 #include "mlir/IR/PatternMatch.h"
 #include "mlir/IR/TypeUtilities.h"
+#include "mlir/IR/ValueRange.h"
 #include "mlir/Interfaces/SubsetOpInterface.h"
 #include "mlir/Interfaces/ValueBoundsOpInterface.h"
 #include "mlir/Support/LLVM.h"
@@ -2394,60 +2395,89 @@ static LogicalResult rewriteFromElementsAsSplat(FromElementsOp fromElementsOp,
 ///
 /// becomes
 ///   %2 = vector.shape_cast %source : vector<1x2xi8> to vector<2xi8>
-static LogicalResult
-rewriteFromElementsAsShapeCast(FromElementsOp fromElementsOp,
-                               PatternRewriter &rewriter) {
+///
+/// The requirements for this to be valid are
+/// i) all elements are extracted from the same vector (source),
+/// ii) source and from_elements result have the same number of elements,
+/// iii) the elements are extracted in ascending order.
+///
+/// It might be possible to rewrite vector.from_elements as a single
+/// vector.extract if (ii) is not satisifed, or in some cases as a
+/// a single vector_extract_strided_slice if (ii) and (iii) are not satisfied,
+/// this is left for future consideration.
+class FromElementsToShapCast : public OpRewritePattern<FromElementsOp> {
+public:
+  using OpRewritePattern::OpRewritePattern;
 
-  // The common source of vector.extract operations (if one exists), as well
-  // as its shape and rank. These are set in the first iteration of the loop
-  // over the operands (elements) of `fromElementsOp`.
-  Value source;
-  ArrayRef<int64_t> shape;
-  int64_t rank;
+  LogicalResult matchAndRewrite(FromElementsOp fromElements,
+                                PatternRewriter &rewriter) const override {
 
-  for (auto [index, element] : llvm::enumerate(fromElementsOp.getElements())) {
+    mlir::OperandRange elements = fromElements.getElements();
+    assert(!elements.empty() && "must be at least 1 element");
 
-    // Check that the element is defined by an extract operation, and that
-    // the extract is on the same vector as all preceding elements.
-    auto extractOp =
-        dyn_cast_if_present<vector::ExtractOp>(element.getDefiningOp());
-    if (!extractOp)
-      return failure();
-    Value currentSource = extractOp.getVector();
-    if (index == 0) {
-      source = currentSource;
-      shape = extractOp.getSourceVectorType().getShape();
-      rank = shape.size();
-    } else if (currentSource != source) {
-      return failure();
+    Value firstElement = elements.front();
+    ExtractOp extractOp =
+        dyn_cast_if_present<vector::ExtractOp>(firstElement.getDefiningOp());
+    if (!extractOp) {
+      return rewriter.notifyMatchFailure(
+          fromElements, "first element not from vector.extract");
     }
+    VectorType sourceType = extractOp.getSourceVectorType();
+    Value source = extractOp.getVector();
 
-    // Check that the (linearized) index of extraction is the same as the index
-    // in the result of `fromElementsOp`.
-    ArrayRef<int64_t> position = extractOp.getStaticPosition();
-    assert(position.size() == rank &&
-           "scalar extract must have full rank position");
-    int64_t stride{1};
-    int64_t offset{0};
-    for (auto [pos, size] :
-         llvm::zip(llvm::reverse(position), llvm::reverse(shape))) {
-      if (pos == ShapedType::kDynamic)
-        return failure();
-      offset += pos * stride;
-      stride *= size;
+    // Check condition (ii).
+    if (static_cast<size_t>(sourceType.getNumElements()) != elements.size()) {
+      return rewriter.notifyMatchFailure(fromElements,
+                                         "number of elements differ");
     }
-    if (offset != index)
-      return failure();
-  }
 
-  rewriter.replaceOpWithNewOp<ShapeCastOp>(fromElementsOp,
-                                           fromElementsOp.getType(), source);
-}
+    for (auto [indexMinusOne, element] :
+         llvm::enumerate(elements.drop_front(1))) {
+
+      extractOp =
+          dyn_cast_if_present<vector::ExtractOp>(element.getDefiningOp());
+      if (!extractOp) {
+        return rewriter.notifyMatchFailure(fromElements,
+                                           "element not from vector.extract");
+      }
+      Value currentSource = extractOp.getVector();
+      // Check condition (i).
+      if (currentSource != source) {
+        return rewriter.notifyMatchFailure(fromElements,
+                                           "element from different vector");
+      }
+
+      ArrayRef<int64_t> position = extractOp.getStaticPosition();
+      assert(position.size() == static_cast<size_t>(sourceType.getRank()) &&
+             "scalar extract must have full rank position");
+      int64_t stride{1};
+      int64_t offset{0};
+      for (auto [pos, size] : llvm::zip(llvm::reverse(position),
+                                        llvm::reverse(sourceType.getShape()))) {
+        if (pos == ShapedType::kDynamic) {
+          return rewriter.notifyMatchFailure(
+              fromElements, "elements not in ascending order (dynamic order)");
+        }
+        offset += pos * stride;
+        stride *= size;
+      }
+      // Check condition (iii).
+      if (offset != static_cast<int64_t>(indexMinusOne + 1)) {
+        return rewriter.notifyMatchFailure(
+            fromElements, "elements not in ascending order (static order)");
+      }
+    }
+
+    rewriter.replaceOpWithNewOp<ShapeCastOp>(fromElements,
+                                             fromElements.getType(), source);
+    return success();
+  }
+};
 
 void FromElementsOp::getCanonicalizationPatterns(RewritePatternSet &results,
                                                  MLIRContext *context) {
   results.add(rewriteFromElementsAsSplat);
-  results.add(rewriteFromElementsAsShapeCast);
+  results.add<FromElementsToShapCast>(context);
 }
 
 //===----------------------------------------------------------------------===//
diff --git a/mlir/test/Dialect/Vector/canonicalize/vector-from-elements.mlir b/mlir/test/Dialect/Vector/canonicalize/vector-from-elements.mlir
index fafac4419d719..2899abb07c97c 100644
--- a/mlir/test/Dialect/Vector/canonicalize/vector-from-elements.mlir
+++ b/mlir/test/Dialect/Vector/canonicalize/vector-from-elements.mlir
@@ -143,3 +143,14 @@ func.func @negative_different_sources(%arg0: vector<1x2xi8>, %arg1: vector<1x2xi
   %2 = vector.from_elements %0, %1 : vector<2xi8>
   return %2 : vector<2xi8>
 }
+
+// -----
+
+// CHECK-LABEL: func @negative_source_too_large(
+//   CHECK-NOT: shape_cast
+func.func @negative_source_too_large(%arg0: vector<1x3xi8>) -> vector<2xi8> {
+  %0 = vector.extract %arg0[0, 0] : i8 from vector<1x3xi8>
+  %1 = vector.extract %arg0[0, 1] : i8 from vector<1x3xi8>
+  %2 = vector.from_elements %0, %1 : vector<2xi8>
+  return %2 : vector<2xi8>
+}

>From 28fccebe260d0ddf9bdb48ebde5efe36d7967516 Mon Sep 17 00:00:00 2001
From: James Newling <james.newling at gmail.com>
Date: Wed, 14 May 2025 12:40:11 -0700
Subject: [PATCH 5/5] spacing nit

---
 mlir/lib/Dialect/Vector/IR/VectorOps.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mlir/lib/Dialect/Vector/IR/VectorOps.cpp b/mlir/lib/Dialect/Vector/IR/VectorOps.cpp
index 7b7f014480ccd..1080263ed3eb6 100644
--- a/mlir/lib/Dialect/Vector/IR/VectorOps.cpp
+++ b/mlir/lib/Dialect/Vector/IR/VectorOps.cpp
@@ -2414,8 +2414,8 @@ class FromElementsToShapCast : public OpRewritePattern<FromElementsOp> {
 
     mlir::OperandRange elements = fromElements.getElements();
     assert(!elements.empty() && "must be at least 1 element");
-
     Value firstElement = elements.front();
+
     ExtractOp extractOp =
         dyn_cast_if_present<vector::ExtractOp>(firstElement.getDefiningOp());
     if (!extractOp) {



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