[PATCH] D123581: [RISCV] Teach vsetvli insertion to handle VSETVLIInfo of vl-modified instruction.

[Yeting Kuo via Phabricator via llvm-commits]

fakepaper56 created this revision.
fakepaper56 added reviewers: craig.topper, jacquesguan.
Herald added subscribers: sunshaoce, VincentWu, luke957, StephenFan, vkmr, frasercrmck, evandro, luismarques, apazos, sameer.abuasal, s.egerton, Jim, benna, psnobl, jocewei, PkmX, the_o, brucehoult, MartinMosbeck, rogfer01, edward-jones, zzheng, jrtc27, kito-cheng, niosHD, sabuasal, simoncook, johnrusso, rbar, asb, hiraditya, arichardson.
Herald added a project: All.
fakepaper56 requested review of this revision.
Herald added subscribers: llvm-commits, pcwang-thead, eopXD, MaskRay.
Herald added a project: LLVM.

If an instruction's AVL is a copy of resulted VL of a instruction,
the instruction have same VL if both of them have same Vtype. The patch adds a
new status, VLModified, to avoid consider the VSETVLIInfo of vl-modified
instructions unknonwn and do not insert vsetsvli if the instruction's AVL is
a copy of resulted VL of last instructions.

Take the below C code as an example,

  vint8m4_t vec_src1 = vle8ff_v_i8m4(str1, &new_vl, vl);
  vbool2_t mask1 = vmseq_vx_i8m4_b2(vec_src1, 0, new_vl);

Vsetvli insertion adds a redundant vsetvli for that,

  vsetvli a2,a2,e8,m4,ta,mu
  vle8ff.v  v28,(a0)
  csrr  a3,vl                   ; redundant
  vsetvli zero,a3,e8,m4,ta,mu   ; redundant
  vmseq.vi  v25,v28,0

Although the patch could prevent some redundant vsetvli, those PseudoReadVL
could not be optimized since the pass followed by register allocation.
We could re-run some optimization pass like dead-mi-elimination to solve the
problem.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D123581

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

-------------- next part --------------
A non-text attachment was scrubbed...
Name: D123581.422156.patch
Type: text/x-patch
Size: 11209 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20220412/c9d3bd35/attachment.bin>