[mlir][tosa] Cleanup of tosa.rescale lowering to linalg

[rsuderman]

Summary

Comment was poorly written. Changed to bail on contradictory information in
the double round.

mlir/lib/Conversion/TosaToLinalg/TosaToLinalg.cpp

public:
   LogicalResult matchAndRewrite(tosa::RescaleOp op,
                                 PatternRewriter &rewriter) const final {
     auto loc = op.getLoc();
     auto input = op.input();
     auto inputTy = op.input().getType().cast<ShapedType>();
     auto outputTy = op.output().getType().cast<ShapedType>();
     unsigned rank = inputTy.getRank();
 
+    // This is an illegal configuration. terminate and log an error
+    if (op.double_round() && !op.scale32())
+      return rewriter.notifyMatchFailure(
+          op, "tosa.rescale requires scale32 for double_round to be true");
+
     if (!outputTy.hasStaticShape())
       return rewriter.notifyMatchFailure(
           op, "tosa to linalg conversion expects statically shaped tensors");
 
     // The shift and multiplier values.
     SmallVector<int32_t> multiplierValues;
     getValuesFromIntArrayAttribute(op.multiplier(), multiplierValues);
 

mlir/lib/Conversion/TosaToStandard/TosaToStandard.cpp

if (doubleRound) {
       Value thirty32 = rewriter.create<ConstantOp>(
           loc, rewriter.getIntegerAttr(rewriter.getI32Type(), 30));
 
       Value shiftThirty32 =
           rewriter.create<mlir::ShiftLeftOp>(loc, one32, thirty32);
       Value shiftThirty64 = rewriter.create<mlir::SignExtendIOp>(
           loc, rewriter.getI64Type(), shiftThirty32);
 
-      // Round value needs to with be added or sbustracted depending on
+      // Round value needs to with be added or subtracted depending on the sign
+      // of the input value.
       Value roundAdd64 =
           rewriter.create<mlir::AddIOp>(loc, round64, shiftThirty64);
       Value roundSub64 =
           rewriter.create<mlir::SubIOp>(loc, round64, shiftThirty64);
 
       Value valueGreaterThanZero = rewriter.create<mlir::CmpIOp>(
           loc, CmpIPredicate::sge, value32, zero32);