[PATCH] D133373: [docs][RISCV] Document status of scalar crypto extensions

[Craig Topper via Phabricator via llvm-commits]

craig.topper added inline comments.


================
Comment at: llvm/docs/RISCVUsage.rst:96
+``Zbkb``, ``Zbkx``
+  Pattern matching support for these instructions is incomplete.
+
----------------
reames wrote:
> craig.topper wrote:
> > Can you file an issue for what is missing?
> This wasn't a deep dive.
> 
> For Zbkb, I had observed we could use PACK variants for building constants or build_vectors of small vector types.  Not clear how much we can/should push here.  
> 
> For Zbkx, we appear to have no pattern matching beyond intrinsics.  
We could use PACK for assembling pieces of unaligned loads too.

Zbkx pattern matching is missing and may be hard to do robustly. Maybe we if we did something like `recognizeBSwapOrBitReverseIdiom` where we collect the provenance of every bit. But that could still be fragile if it is proceeded by any extra bit operations.


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https://reviews.llvm.org/D133373