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As for today, the value of DSLX for-loop iterator is not treated as constant when iterating over constant values. Having the ability to use the for-loop iterator in this way can improve the expressiveness of the language. In all these cases, when iterating over constant values it should be possible to unroll the for-loop.
These small examples show the current limitations of the language:
let data = u64:0x00_11_22_33_44_55_66_77;for(i,())in s32:0..s32:8{// works if rewritten with width sliceslet slice = data[(i * s32:8):(i + s32:1)* s32:8];trace_fmt!("slice is {}", slice);}(());// for (i, ()) in s32:0..s32:8 {// let slice = data[(i * s32:8) : (i + s32:1) * s32:8];// ~~~~~~~~~~~~~~~~~~~~~~~~^ TypeInferenceError: Unable to resolve slice start to a compile-time constant.// the unrolled version workslet slice = data[(s32:0* s32:8):(s32:0 + s32:1)* s32:8];let slice = data[(s32:1* s32:8):(s32:1 + s32:1)* s32:8];let slice = data[(s32:2* s32:8):(s32:2 + s32:1)* s32:8];//...let slice = data[(s32:7* s32:8):(s32:7 + s32:1)* s32:8];
fnadd_const<Y:s32>(x:s32) -> s32{ x + Y}for(i, acc)in s32:0..s32:8{
add_const<i>(acc);}((u32:3));// for (i, acc) in s32:0..s32:8 {// add_const<i>(acc);// ~~~~~~~~~~~~~~^ TypeInferenceError: sN[32] Parametric expression `i` was not constexpr -- parametric values must be compile-time constants
An example of data concatenation. We tried to use similar logic as a part of a buffering proc. The proc accumulated incoming data in the state and sent back the requested number of bytes of data.
//This data may come from channelslet s = s32:4;let data1 = u64:0x00_11_22_33_44_55_66_77;let data2 = u64:0x88_99_AA_BB_CC_DD_EE_FF;let slice = for(i, slice)in s32:0..s32:8{if(s == i){
data1[i * s32:8: s32:64] ++ data2[0: i * s32:8]}else{
slice
}}(u64:0);trace_fmt!("slice is {}", slice);let slice = if s == s32:0{data1[s32:0* s32:8: s32:64] ++ data2[0: s32:0* s32:8]}else{u64:0};let slice = if s == s32:1{data1[s32:1* s32:8: s32:64] ++ data2[0: s32:1* s32:8]}else{slice};let slice = if s == s32:2{data1[s32:2* s32:8: s32:64] ++ data2[0: s32:2* s32:8]}else{slice};let slice = if s == s32:3{data1[s32:3* s32:8: s32:64] ++ data2[0: s32:3* s32:8]}else{slice};let slice = if s == s32:4{data1[s32:4* s32:8: s32:64] ++ data2[0: s32:4* s32:8]}else{slice};let slice = if s == s32:5{data1[s32:5* s32:8: s32:64] ++ data2[0: s32:5* s32:8]}else{slice};let slice = if s == s32:6{data1[s32:6* s32:8: s32:64] ++ data2[0: s32:6* s32:8]}else{slice};let slice = if s == s32:7{data1[s32:7* s32:8: s32:64] ++ data2[0: s32:7* s32:8]}else{slice};trace_fmt!("slice: {:#x}", slice);
Current best alternative workaround (limit 100 words)
Unroll the for-loop as in the examples above
Your view of the "best case XLS enhancement" (limit 100 words)
In cases when the for-loop iterates over constant values, the iterator can be treated as a constant and XLS can treat the loop as if it were unrolled
The text was updated successfully, but these errors were encountered:
Note that this is what unroll_for! is for in the DSL -- in a normal type system that doesn't macro expand it doesn't make sense to have one binding (i.e. name in the program) with different types in different loop iterations, which is why having i be constexpr doesn't make as much sense.
I'm not sure how fully supported it is at the moment:
What's hard to do? (limit 100 words)
As for today, the value of DSLX for-loop iterator is not treated as constant when iterating over constant values. Having the ability to use the for-loop iterator in this way can improve the expressiveness of the language. In all these cases, when iterating over constant values it should be possible to unroll the for-loop.
These small examples show the current limitations of the language:
Current best alternative workaround (limit 100 words)
Unroll the for-loop as in the examples above
Your view of the "best case XLS enhancement" (limit 100 words)
In cases when the for-loop iterates over constant values, the iterator can be treated as a constant and XLS can treat the loop as if it were unrolled
The text was updated successfully, but these errors were encountered: