[all-commits] [llvm/llvm-project] 0afc88: [RISCV] Use vnclip for scalable vector saturating ...

[Chia via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 0afc884e874043bf5207d561ab82b107e8860d41
      https://github.com/llvm/llvm-project/commit/0afc884e874043bf5207d561ab82b107e8860d41
  Author: Chia <sun1011jacobi at gmail.com>
  Date:   2024-04-18 (Thu, 18 Apr 2024)

  Changed paths:
    M llvm/lib/Target/RISCV/RISCVInstrInfoVSDPatterns.td
    M llvm/lib/Target/RISCV/RISCVInstrInfoVVLPatterns.td
    A llvm/test/CodeGen/RISCV/rvv/fixed-vectors-trunc-sat-clip.ll
    A llvm/test/CodeGen/RISCV/rvv/trunc-sat-clip-sdnode.ll
    R llvm/test/CodeGen/RISCV/rvv/trunc-sat-clip.ll

  Log Message:
  -----------
  [RISCV] Use vnclip for scalable vector saturating truncation. (#88648)

Similar to #75145, but for scalable vectors.

Specifically, this patch works for the below optimization case:

## Source Code
```
define void @trunc_sat_i8i16_maxmin(ptr %x, ptr %y) {
  %1 = load <vscale x 4 x i16>, ptr %x, align 16
  %2 = tail call <vscale x 4 x i16> @llvm.smax.v4i16(<vscale x 4 x i16> %1, <vscale x 4 x i16> splat (i16 -128))
  %3 = tail call <vscale x 4 x i16> @llvm.smin.v4i16(<vscale x 4 x i16> %2, <vscale x 4 x i16> splat (i16 127))
  %4 = trunc <vscale x 4 x i16> %3 to <vscale x 4 x i8>
  store <vscale x 4 x i8> %4, ptr %y, align 8
  ret void
}
```
## Before this patch
[Compiler Explorer](https://godbolt.org/z/EKc9eGvo8)
```
trunc_sat_i8i16_maxmin:
        vl1re16.v       v8, (a0)
        li      a0, -128
        vsetvli a2, zero, e16, m1, ta, ma
        vmax.vx v8, v8, a0
        li      a0, 127
        vmin.vx v8, v8, a0
        vsetvli zero, zero, e8, mf2, ta, ma
        vnsrl.wi        v8, v8, 0
        vse8.v  v8, (a1)
        ret
```
## After this patch
```
trunc_sat_i8i16_maxmin:
        vsetivli zero, 4, e8, mf4, ta, ma
        vle16.v v8, (a0)
        vnclip.wi v8, v8, 0
        vse8.v v8, (a1)
        ret
```



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