[all-commits] [llvm/llvm-project] 87779f: [RISCV][ISel] Remove redundant min/max in saturati...

[Chia via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 87779fd823bb0d619c26449db91c7504ce7513c5
      https://github.com/llvm/llvm-project/commit/87779fd823bb0d619c26449db91c7504ce7513c5
  Author: Chia <sun1011jacobi at gmail.com>
  Date:   2023-12-29 (Fri, 29 Dec 2023)

  Changed paths:
    M llvm/lib/Target/RISCV/RISCVInstrInfoVVLPatterns.td
    M llvm/test/CodeGen/RISCV/rvv/fpclamptosat_vec.ll
    A llvm/test/CodeGen/RISCV/rvv/trunc-sat-clip.ll

  Log Message:
  -----------
  [RISCV][ISel] Remove redundant min/max in saturating truncation (#75145)

This patch closed #73424, which is also a missed-optimization case
similar to #68466 on X86.

## Source Code
```
define void @trunc_sat_i8i16(ptr %x, ptr %y) {
  %1 = load <8 x i16>, ptr %x, align 16
  %2 = tail call <8 x i16> @llvm.smax.v8i16(<8 x i16> %1, <8 x i16> <i16 -128, i16 -128, i16 -128, i16 -128, i16 -128, i16 -128, i16 -128, i16 -128>)
  %3 = tail call <8 x i16> @llvm.smin.v8i16(<8 x i16> %2, <8 x i16> <i16 127, i16 127, i16 127, i16 127, i16 127, i16 127, i16 127, i16 127>)
  %4 = trunc <8 x i16> %3 to <8 x i8>
  store <8 x i8> %4, ptr %y, align 8
  ret void
}
```
## Before this patch: 
```
trunc_sat_i8i16:                  # @trunc_maxmin_id_i8i16
        vsetivli        zero, 8, e16, m1, ta, ma
        vle16.v v8, (a0)
        li      a0, -128
        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:                  # @trunc_maxmin_id_i8i16
	vsetivli	zero, 8, e8, mf2, ta, ma
	vle16.v	v8, (a0)
	csrwi	vxrm, 0
	vnclip.wi	v8, v8, 0
	vse8.v	v8, (a1)
	ret
```