[PATCH] D127576: [RISCV] Teach vsetvli insertion to handle VLEFF/VLSEGFF.

[Yeting Kuo via Phabricator via llvm-commits]

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VSETVLIInfos right after VLEFF/VLSEGFF are unkown since they modify VL. Unknown
VSETVLIInfos make next vector operations needed to be inserted VSET(I)VLI.

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

After D126794 <https://reviews.llvm.org/D126794>, VLEFF/VLSEGFF has a define having value of VL. The patch consider
there is a ghost vsetvli right after VLEFF/VLSEGFF. The ghost VSET(I)LIs use the
vl output of the VLEFF/VLSEGFF as its AVL and same VTYPE of the VLEFF/VLSEGFF.
The ghost vsetvli must be redundant, and we could use it to get the VSETVLIInfo
right after VLEFF/VLSEGFF.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D127576

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

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