[PPC] Movemasks should be emulated without resorting to bit-by-bit logic

[Validark]

Godbolt link

export fn maskForUnderscores(src: [*]const u8) u16 {
    return @bitCast(src[0..@sizeOf(Chunk)].* == @as(@Vector(@sizeOf(Chunk), u8), @splat('_')));
}

Gives:

maskForUnderscores:
        stwu 1, -48(1)
        lxv 34, 0(3)
        xxspltib 35, 95
        vcmpequb 2, 2, 3
        stxv 34, 16(1)
        lbz 3, 31(1)
        lbz 4, 30(1)
        clrlwi  3, 3, 31
        rlwimi 3, 4, 1, 30, 30
        lbz 4, 29(1)
        rlwimi 3, 4, 2, 29, 29
        lbz 4, 28(1)
        rlwimi 3, 4, 3, 28, 28
        lbz 4, 27(1)
        rlwimi 3, 4, 4, 27, 27
        lbz 4, 26(1)
        rlwimi 3, 4, 5, 26, 26
        lbz 4, 25(1)
        rlwimi 3, 4, 6, 25, 25
        lbz 4, 24(1)
        rlwimi 3, 4, 7, 24, 24
        lbz 4, 23(1)
        rlwimi 3, 4, 8, 23, 23
        lbz 4, 22(1)
        rlwimi 3, 4, 9, 22, 22
        lbz 4, 21(1)
        rlwimi 3, 4, 10, 21, 21
        lbz 4, 20(1)
        rlwimi 3, 4, 11, 20, 20
        lbz 4, 19(1)
        rlwimi 3, 4, 12, 19, 19
        lbz 4, 18(1)
        rlwimi 3, 4, 13, 18, 18
        lbz 4, 17(1)
        rlwimi 3, 4, 14, 17, 17
        lbz 4, 16(1)
        rlwimi 3, 4, 15, 16, 16
        addi 1, 1, 48
        blr

Here is one way of compiling a movemask on PowerPC: https://godbolt.org/z/shhcqE7G9

bar(float __vector(4)):
.LCF0:
0:      addis 2,12,.TOC.-.LCF0@ha
        addi 2,2,.TOC.-.LCF0@l
        addis 9,2,.LC0@toc@ha
        addi 9,9,.LC0@toc@l
        lvx 0,0,9
        vbpermq 2,2,0
        mfvsrd 3,34
        extsw 3,3
        blr
        .long 0
        .byte 0,9,0,0,0,0,0,0
.LC0:
        .byte   120
        .byte   112
        .byte   104
        .byte   96
        .byte   88
        .byte   80
        .byte   72
        .byte   64
        .byte   56
        .byte   48
        .byte   40
        .byte   32
        .byte   24
        .byte   16
        .byte   8
        .byte   0

[llvmbot]

@llvm/issue-subscribers-backend-powerpc

Author: Niles Salter (Validark)

[Godbolt link](https://zig.godbolt.org/z/MxTW9d6Kr) ```zig export fn maskForUnderscores(src: [*]const u8) u16 { return @bitCast(src[0..@sizeOf(Chunk)].* == @as(@Vector(@sizeOf(Chunk), u8), @splat('_'))); } ```

Gives:

maskForUnderscores:
        stwu 1, -48(1)
        lxv 34, 0(3)
        xxspltib 35, 95
        vcmpequb 2, 2, 3
        stxv 34, 16(1)
        lbz 3, 31(1)
        lbz 4, 30(1)
        clrlwi  3, 3, 31
        rlwimi 3, 4, 1, 30, 30
        lbz 4, 29(1)
        rlwimi 3, 4, 2, 29, 29
        lbz 4, 28(1)
        rlwimi 3, 4, 3, 28, 28
        lbz 4, 27(1)
        rlwimi 3, 4, 4, 27, 27
        lbz 4, 26(1)
        rlwimi 3, 4, 5, 26, 26
        lbz 4, 25(1)
        rlwimi 3, 4, 6, 25, 25
        lbz 4, 24(1)
        rlwimi 3, 4, 7, 24, 24
        lbz 4, 23(1)
        rlwimi 3, 4, 8, 23, 23
        lbz 4, 22(1)
        rlwimi 3, 4, 9, 22, 22
        lbz 4, 21(1)
        rlwimi 3, 4, 10, 21, 21
        lbz 4, 20(1)
        rlwimi 3, 4, 11, 20, 20
        lbz 4, 19(1)
        rlwimi 3, 4, 12, 19, 19
        lbz 4, 18(1)
        rlwimi 3, 4, 13, 18, 18
        lbz 4, 17(1)
        rlwimi 3, 4, 14, 17, 17
        lbz 4, 16(1)
        rlwimi 3, 4, 15, 16, 16
        addi 1, 1, 48
        blr

Here is one way of compiling a movemask on PowerPC: https://godbolt.org/z/shhcqE7G9

bar(float __vector(4)):
.LCF0:
0:      addis 2,12,.TOC.-.LCF0@<!-- -->ha
        addi 2,2,.TOC.-.LCF0@<!-- -->l
        addis 9,2,.LC0@<!-- -->toc@<!-- -->ha
        addi 9,9,.LC0@<!-- -->toc@<!-- -->l
        lvx 0,0,9
        vbpermq 2,2,0
        mfvsrd 3,34
        extsw 3,3
        blr
        .long 0
        .byte 0,9,0,0,0,0,0,0
.LC0:
        .byte   120
        .byte   112
        .byte   104
        .byte   96
        .byte   88
        .byte   80
        .byte   72
        .byte   64
        .byte   56
        .byte   48
        .byte   40
        .byte   32
        .byte   24
        .byte   16
        .byte   8
        .byte   0

[chenzheng1030]

hi @Validark could you help to post the LLVM IR for the zig source? Thanks.

[Validark]

@chenzheng1030 Here you go: https://godbolt.org/z/vG1d93K37

define dso_local zeroext i16 @maskForUnderscores(ptr nocapture nonnull readonly align 1 %0) local_unnamed_addr {
Entry:
  %1 = load <16 x i8>, ptr %0, align 1
  %2 = icmp eq <16 x i8> %1, <i8 95, i8 95, i8 95, i8 95, i8 95, i8 95, i8 95, i8 95, i8 95, i8 95, i8 95, i8 95, i8 95, i8 95, i8 95, i8 95>
  %3 = bitcast <16 x i1> %2 to i16
  ret i16 %3
}

declare void @llvm.dbg.value(metadata, metadata, metadata) #1