[PATCH] D148735: [RISCV][WIP] Use vsetvli x0, x0 in more cases.

[Craig Topper via Phabricator via llvm-commits]

craig.topper created this revision.
craig.topper added reviewers: reames, frasercrmck, rogfer01, kito-cheng, michaelmaitland.
Herald added subscribers: jobnoorman, luke, VincentWu, vkmr, evandro, luismarques, apazos, sameer.abuasal, s.egerton, Jim, benna, psnobl, jocewei, PkmX, the_o, brucehoult, MartinMosbeck, edward-jones, zzheng, jrtc27, shiva0217, niosHD, sabuasal, simoncook, johnrusso, rbar, asb, hiraditya, arichardson.
Herald added a project: All.
craig.topper requested review of this revision.
Herald added subscribers: pcwang-thead, eopXD, MaskRay.
Herald added a project: LLVM.

If the AVL is a virtual register defined by a vsetvli with the same
vlmax we need and the previous vsetvli we saw in the data flow also
has that vlmax, we can use the x0, x0 form when we insert a vsetvli.

Not only does this avoid an update of the VL physical register, but
it may allow doLocalPostpass to completely remove the inserted vsetvli
by rewriting the vtype of the previous vsetvli.

The modified test shows the vsetvli being removed. I will add some
more tests to this patch today.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D148735

Files:
  llvm/lib/Target/RISCV/RISCVInsertVSETVLI.cpp
  llvm/test/CodeGen/RISCV/rvv/vsetvli-insert.ll

-------------- next part --------------
A non-text attachment was scrubbed...
Name: D148735.515047.patch
Type: text/x-patch
Size: 5034 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20230419/b92bb02b/attachment.bin>