[all-commits] [llvm/llvm-project] 1c7ec0: [VPlan] Optimize LastActiveLane to EVL - 1 (#169766)

[Luke Lau via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 1c7ec06b16dc59b5b52cff95bde7d5330ffa0293
      https://github.com/llvm/llvm-project/commit/1c7ec06b16dc59b5b52cff95bde7d5330ffa0293
  Author: Luke Lau <luke at igalia.com>
  Date:   2025-11-27 (Thu, 27 Nov 2025)

  Changed paths:
    M llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
    M llvm/test/Transforms/LoopVectorize/RISCV/dead-ops-cost.ll
    M llvm/test/Transforms/LoopVectorize/RISCV/divrem.ll
    M llvm/test/Transforms/LoopVectorize/RISCV/first-order-recurrence-scalable-vf1.ll
    M llvm/test/Transforms/LoopVectorize/RISCV/scalable-tailfold.ll
    M llvm/test/Transforms/LoopVectorize/RISCV/tail-folding-fixed-order-recurrence.ll
    M llvm/test/Transforms/LoopVectorize/RISCV/uniform-load-store.ll

  Log Message:
  -----------
  [VPlan] Optimize LastActiveLane to EVL - 1 (#169766)

With EVL tail folding, the LastActiveLane can be computed with EVL - 1.
This removes the need for a header mask and vfirst.m for loops with live
outs on RISC-V:

     # %bb.5:                                # %for.cond.cleanup7
    -       vsetvli zero, zero, e32, m2, ta, ma
    -       vmv.v.x v8, s1
    -       vmsleu.vv       v10, v8, v22
    -       vfirst.m        a0, v10
    -       srli    a1, a0, 63
    -       czero.nez       a0, a0, a1
    -       czero.eqz       a1, s8, a1
    -       or      a0, a0, a1
    -       addi    a0, a0, -1
    -       vsetvli zero, zero, e64, m4, ta, ma
    -       vslidedown.vx   v8, v12, a0
    +       addi    s1, s1, -1
    +       vslidedown.vx   v8, v12, s1



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