FSE decoding improvements in ZSTD

[laudominik]

In this PR the following changes have been made:

• FSE decoder now makes requests to RefillingShiftBuffer in bulks
• FSE decoder sends LITERAL and SEQUENCE commands to SequenceExecutor at the same step
• dropped uses of logshift{l,r} in FseDecoder, AxiRamReader and ShiftBuffer

[dplassgit]

Is this ready for review?

[tmichalak]

@dplassgit yes it is.

[dplassgit]

Approval with request for reformatting.

[dplassgit]

Funny formatting here, and other places int his file. You should be able to format with the command line tool.

[rw1nkler]

I reformatted the code as requested

[dplassgit]

Looks like zstd_dec_dslx_test is failing:

xls/modules/zstd/zstd_dec.x:246:26-246:37
0244:         let tok0 = join();
0245: 
0246:         const CSR_REQS = CsrRdReq[2]:[
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^---------^ TypeInferenceError: CsrRdReq { csr: uN[LOG2_REGS_N] }[2] Annotated type for array literal must be constexpr; type has dimensions that cannot be resolved.
0247:             CsrRdReq {csr: csr<LOG2_REGS_N>(Csr::INPUT_BUFFER)},
0248:             CsrRdReq {csr: csr<LOG2_REGS_N>(Csr::OUTPUT_BUFFER)}

[rw1nkler]

This is interesting. It looks like the proc-scoped type is treated in different way than a local type alias, because the error disappears after redefining the type in the next's body:

diff --git a/xls/modules/zstd/zstd_dec.x b/xls/modules/zstd/zstd_dec.x
index a68ed6514..11af2a7fc 100644
--- a/xls/modules/zstd/zstd_dec.x
+++ b/xls/modules/zstd/zstd_dec.x
@@ -243,6 +243,7 @@ proc ZstdDecoderInternal<
     next (state: State) {
         let tok0 = join();

+        type CsrRdReq = csr_config::CsrRdReq<LOG2_REGS_N>;
         const CSR_REQS = CsrRdReq[2]:[
             CsrRdReq {csr: csr<LOG2_REGS_N>(Csr::INPUT_BUFFER)},
             CsrRdReq {csr: csr<LOG2_REGS_N>(Csr::OUTPUT_BUFFER)}

or after referencing the type without the proc-scoped alias:

diff --git a/xls/modules/zstd/zstd_dec.x b/xls/modules/zstd/zstd_dec.x
index a68ed6514..d22927ad3 100644
--- a/xls/modules/zstd/zstd_dec.x
+++ b/xls/modules/zstd/zstd_dec.x
@@ -243,7 +243,7 @@ proc ZstdDecoderInternal<
     next (state: State) {
         let tok0 = join();

-        const CSR_REQS = CsrRdReq[2]:[
+        const CSR_REQS = csr_config::CsrRdReq<LOG2_REGS_N>[2]:[
             CsrRdReq {csr: csr<LOG2_REGS_N>(Csr::INPUT_BUFFER)},
             CsrRdReq {csr: csr<LOG2_REGS_N>(Csr::OUTPUT_BUFFER)}
         ];

[rw1nkler]

Superseded by #3034

[tmichalak]

@proppy @dplassgit since #3034 got merged this one can be closed.

[dplassgit]

Closed since #3034 supersedes it and is merged.