[Mlir-commits] [mlir] [mlir][LLVM] Fix unsupported FP lowering in `VectorConvertToLLVMPattern` (PR #166513)

[Matthias Springer]

https://github.com/matthias-springer created https://github.com/llvm/llvm-project/pull/166513

Fixes a bug in `VectorConvertToLLVMPattern`, which converted operations with unsupported FP types. E.g., `arith.addf ... : f4E2M1FN` was lowered to `llvm.fadd ... : i4`, which does not verify.


>From 6eb0454c03888a79a4cd33f30fa8b3026f971439 Mon Sep 17 00:00:00 2001
From: Matthias Springer <me at m-sp.org>
Date: Wed, 5 Nov 2025 07:08:47 +0000
Subject: [PATCH] [mlir][LLVM] Fix unsupported FP lowering in
 `VectorConvertToLLVMPattern`

---
 .../Conversion/LLVMCommon/VectorPattern.h     | 25 ++++++++++++++++++
 .../Conversion/ArithToLLVM/arith-to-llvm.mlir | 26 +++++++++++++++++++
 2 files changed, 51 insertions(+)

diff --git a/mlir/include/mlir/Conversion/LLVMCommon/VectorPattern.h b/mlir/include/mlir/Conversion/LLVMCommon/VectorPattern.h
index 964281592cc65..d8483114f1137 100644
--- a/mlir/include/mlir/Conversion/LLVMCommon/VectorPattern.h
+++ b/mlir/include/mlir/Conversion/LLVMCommon/VectorPattern.h
@@ -92,12 +92,37 @@ class VectorConvertToLLVMPattern : public ConvertOpToLLVMPattern<SourceOp> {
   using ConvertOpToLLVMPattern<SourceOp>::ConvertOpToLLVMPattern;
   using Super = VectorConvertToLLVMPattern<SourceOp, TargetOp>;
 
+  /// Return "true" if the given type (or its element type) is a floating point
+  /// type.
+  static FloatType getFloatingPointType(Type type) {
+    if (auto floatType = dyn_cast<FloatType>(type))
+      return floatType;
+    if (auto vecType = dyn_cast<VectorType>(type))
+      return dyn_cast<FloatType>(vecType.getElementType());
+    return nullptr;
+  }
+
   LogicalResult
   matchAndRewrite(SourceOp op, typename SourceOp::Adaptor adaptor,
                   ConversionPatternRewriter &rewriter) const override {
     static_assert(
         std::is_base_of<OpTrait::OneResult<SourceOp>, SourceOp>::value,
         "expected single result op");
+
+    // The pattern should not apply if a floating-point operand is converted to
+    // a non-floating-point type. This indicates that the floating point type
+    // is not supported by the LLVM lowering. (Such types are converted to
+    // integers.)
+    for (Value operand : op->getOperands()) {
+      FloatType floatType = getFloatingPointType(operand.getType());
+      if (!floatType)
+        continue;
+      Type convertedType = this->getTypeConverter()->convertType(floatType);
+      if (!isa<FloatType>(convertedType))
+        return rewriter.notifyMatchFailure(op,
+                                           "unsupported floating point type");
+    }
+
     // Determine attributes for the target op
     AttrConvert<SourceOp, TargetOp> attrConvert(op);
 
diff --git a/mlir/test/Conversion/ArithToLLVM/arith-to-llvm.mlir b/mlir/test/Conversion/ArithToLLVM/arith-to-llvm.mlir
index ba12ff29ebef9..b5dcb01d3dc6b 100644
--- a/mlir/test/Conversion/ArithToLLVM/arith-to-llvm.mlir
+++ b/mlir/test/Conversion/ArithToLLVM/arith-to-llvm.mlir
@@ -747,3 +747,29 @@ func.func @memref_bitcast(%1: memref<?xi16>) -> memref<?xbf16> {
   %2 = arith.bitcast %1 : memref<?xi16> to memref<?xbf16>
   func.return %2 : memref<?xbf16>
 }
+
+// -----
+
+// CHECK-LABEL: func @unsupported_fp_type
+//       CHECK:   arith.addf {{.*}} : f4E2M1FN
+//       CHECK:   arith.addf {{.*}} : vector<4xf4E2M1FN>
+//       CHECK:   arith.addf {{.*}} : vector<8x4xf4E2M1FN>
+func.func @unsupported_fp_type(%arg0: f4E2M1FN, %arg1: vector<4xf4E2M1FN>, %arg2: vector<8x4xf4E2M1FN>) -> (f4E2M1FN, vector<4xf4E2M1FN>, vector<8x4xf4E2M1FN>) {
+  %0 = arith.addf %arg0, %arg0 : f4E2M1FN
+  %1 = arith.addf %arg1, %arg1 : vector<4xf4E2M1FN>
+  %2 = arith.addf %arg2, %arg2 : vector<8x4xf4E2M1FN>
+  return %0, %1, %2 : f4E2M1FN, vector<4xf4E2M1FN>, vector<8x4xf4E2M1FN>
+}
+
+// -----
+
+//   CHECK-LABEL: func @supported_fp_type
+//         CHECK:   llvm.fadd {{.*}} : f32
+//         CHECK:   llvm.fadd {{.*}} : vector<4xf32>
+// CHECK-COUNT-4:   llvm.fadd {{.*}} : vector<8xf32>
+func.func @supported_fp_type(%arg0: f32, %arg1: vector<4xf32>, %arg2: vector<4x8xf32>) -> (f32, vector<4xf32>, vector<4x8xf32>) {
+  %0 = arith.addf %arg0, %arg0 : f32
+  %1 = arith.addf %arg1, %arg1 : vector<4xf32>
+  %2 = arith.addf %arg2, %arg2 : vector<4x8xf32>
+  return %0, %1, %2 : f32, vector<4xf32>, vector<4x8xf32>
+}