Test has incorrect lowering

[Mark1626]

The test file-tests/should-lower/hoist.fuse fails typecheck as there is an out of bounds access let w = b[10 * 12];. However when --lower is present it seems to pass.

decl a: bit<32>[1];
decl b: bit<32>[1];

// Recusively hoist nested reads
let x = a[b[0]];
---

// Hoist binary expressions with reads
let y = 10 + a[0];

// Recusively hoist slow ops
let z = (x * 10) / (y * 20 - 15);

// Recursively hoist slow index expressions
let w = b[10 * 12];

// Complex chained binary expression
let k = (((0-1) * 1 + (2*2) * 2 - 1*1 - 1*2) as ubit<32>);

Error without --lower

[WARN] [5.11] bit<32> is used for an array access. This might be out of bounds at runtime.
let x = a[b[0]];
          ^

[Type error] [Line 15, Column 11] Index out of bounds for `b'. Memory size is 1, iterator max val is 120
let w = b[10 * 12];
          ^

[rachitnigam]

That's odd! Lowering should still go through the type checker. Can you try using --log info or --log debug to see what's going wrong? Maybe a type checking pass is not being correctly run. FWIW, bounds checking is not a part of the type checker and instead a different pass so possible that the logic is wrong and we miss that pass

[Mark1626]

Issue is in the typecheck. I'll see if I can find a fix

Error from --log debug

[INFO] fuselang.passes.BoundsChecker$BCheck$$anonfun$myCheckE$1$$anonfun$applyOrElse$3.$anonfun$applyOrElse$6(BoundsCheck.scala:84)
fuselang.passes.BoundsChecker$BCheck$$anonfun$myCheckE$1$$anonfun$applyOrElse$3.$anonfun$applyOrElse$6$adapted(BoundsCheck.scala:71)
scala.Option.foreach(Option.scala:437)
fuselang.passes.BoundsChecker$BCheck$$anonfun$myCheckE$1$$anonfun$applyOrElse$3.$anonfun$applyOrElse$5(BoundsCheck.scala:71)
fuselang.passes.BoundsChecker$BCheck$$anonfun$myCheckE$1$$anonfun$applyOrElse$3.$anonfun$applyOrElse$5$adapted(BoundsCheck.scala:69)
scala.collection.immutable.List.foreach(List.scala:333)
fuselang.passes.BoundsChecker$BCheck$$anonfun$myCheckE$1$$anonfun$applyOrElse$3.applyOrElse(BoundsCheck.scala:69)
fuselang.passes.BoundsChecker$BCheck$$anonfun$myCheckE$1$$anonfun$applyOrElse$3.applyOrElse(BoundsCheck.scala:64)
scala.PartialFunction$OrElse.apply(PartialFunction.scala:266)
fuselang.common.Syntax$RichType.matchOrError(Syntax.scala:327)

[Type error] [Line 15, Column 11] Index out of bounds for `b'. Memory size is 1, iterator max val is 120
let w = b[10 * 12];
          ^

Bounds check can be bypassed if the index is stored in a variable

Minimal example

The following fails as expected

decl b: bit<32>[1];

let x = b[10 * 12];

This passes when it should not

decl b: bit<32>[1];

let idx = 10 * 12;
let x = b[idx];

---

In the test --lower raised the constant index to a variable

The final generated HLS code

    ap_int<7> bin_read3_ = ((ap_int<7>)10 * (ap_int<7>)12);
    //---
    ap_int<32> w_ = b[(ap_uint<1>)bin_read3_];

[Mark1626]

I guess this case could be considered valid.

decl b: bit<32>[1];

let idx = 10 * 12;
let x = b[idx];

It's possible for a variable to change

decl b: bit<32>[1];

let idx = 10 * 12;
let x = b[idx];
---
idx := 1

It can be inlined if either if it's marked as a constant or a compilation pass inlines it.