[mlir][spirv] Fail vector.bitcast conversion with different bitwidth

[antiagainst]

Summary

Depending on the target environment, we may need to emulate certain
types, which can cause issue with bitcast.

[ThomasRaoux]

mlir/lib/Conversion/VectorToSPIRV/VectorToSPIRV.cpp

40

you can use getSizeInBits() instead.

62

typo: destination

mlir/lib/Conversion/VectorToSPIRV/VectorToSPIRV.cpp

 #include "mlir/Dialect/SPIRV/Transforms/SPIRVConversion.h"
 #include "mlir/Dialect/Vector/IR/VectorOps.h"
 #include "mlir/IR/BuiltinAttributes.h"
 #include "mlir/IR/BuiltinTypes.h"
 #include "mlir/IR/Matchers.h"
 #include "mlir/Transforms/DialectConversion.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/STLExtras.h"
+#include "llvm/Support/FormatVariadic.h"
 #include <numeric>
 
 using namespace mlir;
 
 /// Gets the first integer value from `attr`, assuming it is an integer array
 /// attribute.
 static uint64_t getFirstIntValue(ArrayAttr attr) {
   return (*attr.getAsValueRange<IntegerAttr>().begin()).getZExtValue();
 }
 
+/// Returns the number of bits for the given scalar/vector type.
+static int getNumBits(Type type) {
+  if (auto vectorType = type.dyn_cast<VectorType>())
+    return vectorType.cast<ShapedType>().getSizeInBits();
+  return type.getIntOrFloatBitWidth();
+}
+
 namespace {
 
 struct VectorBitcastConvert final
     : public OpConversionPattern<vector::BitCastOp> {
   using OpConversionPattern::OpConversionPattern;
 
   LogicalResult
   matchAndRewrite(vector::BitCastOp bitcastOp, OpAdaptor adaptor,
                   ConversionPatternRewriter &rewriter) const override {
     Type dstType = getTypeConverter()->convertType(bitcastOp.getType());
     if (!dstType)
       return failure();
 
-    if (dstType == adaptor.getSource().getType())
+    if (dstType == adaptor.getSource().getType()) {
       rewriter.replaceOp(bitcastOp, adaptor.getSource());
-    else
-      rewriter.replaceOpWithNewOp<spirv::BitcastOp>(bitcastOp, dstType,
-                                                    adaptor.getSource());
-
+      return success();
+    }
+
+    // Check that the source and destination type have the same bitwidth.
+    // Depending on the target environment, we may need to emulate certain
+    // types, which can cause issue with bitcast.
+    Type srcType = adaptor.getSource().getType();
+    if (getNumBits(dstType) != getNumBits(srcType)) {
+      return rewriter.notifyMatchFailure(
+          bitcastOp,
+          llvm::formatv("different source ({0}) and target ({1}) bitwidth",
+                        srcType, dstType));
+    }
+
     return success();
   }
 };
 
 struct VectorBroadcastConvert final
     : public OpConversionPattern<vector::BroadcastOp> {
   using OpConversionPattern::OpConversionPattern;
 

mlir/test/Conversion/VectorToSPIRV/vector-to-spirv.mlir

func.func @bitcast(%arg0 : vector<2xf32>, %arg1: vector<2xf16>) -> (vector<4xf16>, vector<1xf32>) {
   %1 = vector.bitcast %arg1 : vector<2xf16> to vector<1xf32>
   return %0, %1: vector<4xf16>, vector<1xf32>
 }
 
 } // end module
 
 // -----
 
+// Check that without the proper capability we fail the pattern application
+// to avoid generating invalid ops.
+
+module attributes { spirv.target_env = #spirv.target_env<#spirv.vce<v1.0, [], []>, #spirv.resource_limits<>> } {
+
+// CHECK-LABEL: @bitcast
+func.func @bitcast(%arg0 : vector<2xf32>, %arg1: vector<2xf16>) -> (vector<4xf16>, vector<1xf32>) {
+  // CHECK-COUNT-2: vector.bitcast
+  %0 = vector.bitcast %arg0 : vector<2xf32> to vector<4xf16>
+  %1 = vector.bitcast %arg1 : vector<2xf16> to vector<1xf32>
+  return %0, %1: vector<4xf16>, vector<1xf32>
+}
+
+} // end module
+
+// -----
+
 module attributes { spirv.target_env = #spirv.target_env<#spirv.vce<v1.0, [Kernel], []>, #spirv.resource_limits<>> } {
 
 // CHECK-LABEL: @cl_fma
 //  CHECK-SAME: %[[A:.*]]: vector<4xf32>, %[[B:.*]]: vector<4xf32>, %[[C:.*]]: vector<4xf32>
 //       CHECK:   spirv.CL.fma %[[A]], %[[B]], %[[C]] : vector<4xf32>
 func.func @cl_fma(%a: vector<4xf32>, %b: vector<4xf32>, %c: vector<4xf32>) -> vector<4xf32> {
   %0 = vector.fma %a, %b, %c: vector<4xf32>
   return %0 : vector<4xf32>