[mlir][tosa] tosa.cast support for unsigned integers

[rsuderman]

Summary

Unsigned integers need to be handled for cast to floating point.

[rsuderman]

Added test.

mlir/lib/Conversion/TosaToLinalg/TosaToLinalg.cpp

if (srcTy.isInteger(1) && dstTy.isa<IntegerType>() && bitExtend)
       return rewriter.create<mlir::ZeroExtendIOp>(loc, resultTypes, args,
                                                   mlir::None);
 
     // All other si-to-fp conversions should be handled by SIToFP.
     if (mlir::SIToFPOp::areCastCompatible(srcTy, dstTy))
       return rewriter.create<mlir::SIToFPOp>(loc, resultTypes, args,
                                              mlir::None);
 
+    // Unsigned integers need an unrealized cast so that they can be passed
+    // to UIToFP.
+    if (srcTy.isUnsignedInteger() && dstTy.isa<FloatType>()) {
+      auto unrealizedCast =
+          rewriter
+              .create<UnrealizedConversionCastOp>(
+                  loc, rewriter.getIntegerType(srcTy.getIntOrFloatBitWidth()),
+                  args[0])
+              .getResult(0);
+      return rewriter.create<mlir::UIToFPOp>(loc, resultTypes[0],
+                                             unrealizedCast);
+    }
+
     // Casting to boolean, floats need to only be checked as not-equal to zero.
     if (srcTy.isa<FloatType>() && dstTy.isInteger(1)) {
       Value zero =
           rewriter.create<ConstantOp>(loc, rewriter.getFloatAttr(srcTy, 0.0));
       return rewriter.create<mlir::CmpFOp>(loc, CmpFPredicate::UNE,
                                            args.front(), zero);
     }
 

mlir/test/Conversion/TosaToLinalg/tosa-to-linalg.mlir

func @test_simple_i32(%arg0: tensor<1xi32>) -> () {
   // CHECK: select
   %25 = "tosa.abs"(%arg0) : (tensor<1xi32>) -> tensor<1xi32>
 
   return
 }
 
 // -----
 
+// CHECK-LABEL: @test_simple_ui8
+func @test_simple_ui8(%arg0: tensor<1xui8>) -> () {
+
+  // CHECK: linalg.generic
+  // CHECK: uitofp
+  %0 = "tosa.cast"(%arg0) : (tensor<1xui8>) -> tensor<1xf32>
+
+  return
+}
+
+// -----
+
 // CHECK-LABEL: @test_i8
 func @test_i8(%arg0: tensor<1xi8>) -> () {
   // CHECK: linalg.generic
   // CHECK-DAG: %[[C127:.+]] = constant -127
   // CHECK-DAG: %[[C126:.+]] = constant 126
   // CHECK-DAG: %[[CMP1:.+]] = cmpi slt, %arg1, %[[C127]]
   // CHECK-DAG: %[[SEL1:.+]] = select %[[CMP1]], %[[C127]]
   // CHECK-DAG: %[[CMP2:.+]] = cmpi slt, %[[C126]], %arg1