[mlir][tosa] Add lowering to tosa.abs for integer cases

[rsuderman]

Summary

Integer case requires decomposing to simple LLVM operatons.

[rsuderman]

Updated test to pass.

mlir/lib/Conversion/TosaToLinalg/TosaToLinalg.cpp

createLinalgBodyCalculationForElementwiseOp(Operation *op, ValueRange args,
   Location loc = op->getLoc();
   auto elementTy =
       op->getOperand(0).getType().cast<ShapedType>().getElementType();
 
   // tosa::AbsOp
   if (isa<tosa::AbsOp>(op) && elementTy.isa<FloatType>())
     return rewriter.create<mlir::AbsFOp>(loc, resultTypes, args);
 
+  if (isa<tosa::AbsOp>(op) && elementTy.isa<IntegerType>()) {
+    auto zero =
+        rewriter.create<mlir::ConstantOp>(loc, rewriter.getZeroAttr(elementTy));
+    auto cmp =
+        rewriter.create<mlir::CmpIOp>(loc, CmpIPredicate::sgt, args[0], zero);
+    auto neg = rewriter.create<mlir::SubIOp>(loc, zero, args[0]);
+    return rewriter.create<mlir::SelectOp>(loc, cmp, args[0], neg);
+  }
+
   // tosa::AddOp
   if (isa<tosa::AddOp>(op) && elementTy.isa<FloatType>())
     return rewriter.create<mlir::AddFOp>(loc, resultTypes, args);
 
   if (isa<tosa::AddOp>(op) && elementTy.isa<IntegerType>())
     return rewriter.create<mlir::AddIOp>(loc, resultTypes, args);
 
   // tosa::SubOp

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

func @test_simple_i32(%arg0: tensor<1xi32>) -> () {
   // CHECK: constant 0
   // CHECK: cmpi
   %22 = "tosa.cast"(%0) : (tensor<1xi32>) -> tensor<1xi1>
 
   // CHECK: linalg.generic
   // CHECK: sitofp
   %23 = "tosa.cast"(%0) : (tensor<1xi32>) -> tensor<1xf32>
 
+  // CHECK: linalg.generic
+  // CHECK: constant 0
+  // CHECK: cmpi sgt
+  // CHECK: subi
+  // CHECK: select
+  %24 = "tosa.abs"(%arg0) : (tensor<1xi32>) -> tensor<1xi32>
+
   return
 }
 
 // -----
 
 // CHECK-LABEL: @test_bool
 func @test_bool(%arg0: tensor<1xi1>, %arg1: tensor<1xi1>) -> () {
   // CHECK: linalg.generic