<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/152900>152900</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [AVX-512] Consider using `vpshufb(@splat(0xFF), x)` when selecting on `x < 0x80`
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            new issue
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          Validark
      </td>
    </tr>
</table>

<pre>
    For code like this: [Zig Godbolt](https://zig.godbo.lt/#z:OYLghAFBqd5QCxAYwPYBMCmBRdBLAF1QCcAaPECAMzwBtMA7AQwFtMQByARg9KtQYEAysib0QXAEx8BBAKoBnTAAUAHpwAMvAFYTStJg1AAvPMFJL6yAngGVG6AMKpaAVxYMQ0hwBk8DTAA5dwAjTGIQADZSAAdUBUJbBmc3Dy9Y%2BMSBPwDgljCI6MtMayShAiZiAhT3T2li0oFyyoIcoNDwqIsKqpq0%2Bp7W/3b8zsiASgtUV2Jkdg5MVTiqgGoqBjXUVAh1FYABADUSomIISIAWUhXXAA5JlYBPEH2j6xIzy%2Bu78Zfj94urrcfgBSADsACFgRoAIIrOErYiYAgzDZ7BoECC3K6qFbAgDMjn2TAUEEOf1OAK%2B9zRMQMGI0qhuGnGkyhsPhHIepDZHI5e2JpNeJw%2BgLuVxpdIgzNZMI543xkJhYIAImy2YtlgQ1hsQpUds8yW8KZ8gVcnr8jSKqT9DcLKUDcRCefDEcjiBsHrjJJEVgA3GIKBCuKghUkC23/E1i/YKWlMemqABiiZZ2PleMV0JVaphaAYCi1BfQuLxyv2eBYmogwMkkiLNck6czeYLKxCrjoNg2%2BLLewrVYb7c7/gbTZz0JbWqEcgA4jPsEIACrYZUAfQO2Ecq6EAEkAFrYZ74xNoSs2Nir/xansrIsAOgSLHQD9cwGAmALQpIPkYwAICETEhHBiVxMRuK4h1oLs72QECxyVGF1j9AMgxDCAKhCcQVkMB4CAeGJMCufx8DmBRnhwvCCJ%2BPAqBWUkEmMTAAHkqFJRd8OY1jiLwUiWRLbAYzwRiWLYjiRIw%2BgWRtdiCJE7jeJWTBaCUfYZM49CmEwzAQSdWV4Roui%2B2SVAzwrTAIB%2BEgVmnOcF2XNcNy3XcDxLVVSxWBhXFoWgdMzXl4V9SoEQ/LyCANNS5IYEiPxBdzXCizAaACdAFWdfz%2BGIOiNDvO89hCQghCE9S9giriop4mKfgAehWO5HUcPAwUJME/P83lJxWYjFlczrytI4EAFZwUaga3NatqXRCqDBuGwayxvAyIC6nF8WwG8GSZH4NEU5TMBWCTMBm5avQGwz8uEIqRJKsTWIOviaruObUr0/zswQ9l/NdFFgoUULno%2Bx1VXejlFrRS7WOu2SyuihQ%2BNWwThIh0qNK0qTHXG3kvvdZDA2DUN70fZ9EQI%2BN6PB0SoaWvrKquO6iOp2H/o5N6sxezraLJxGKfUu7YoEmz5yXFd103bd92wO9j18tLeUCzKYhaMjcSGsGuchnnNMk6rrNnQX7JFpzxclvFEzmiNTgFuzhccsWD2NxNRVist4qwJLMBSjMZZBhhaGGTZMurb0FaqBQrmyu8dMcAAqBRaFQAgiKa9Gvba2P47vKOev9XG0IJitn0WAhiCYawUfoIiVkzy2hYc0XnIl48rmr/Wbfr%2B37jzp870L4vS/kj8K6r3Wrdrw27cbnXbJrg3bYbk2WSZtqWYmrHUXOxxiQxYOCEZz22ZZmWOrYf8MAUHqC2IVxrGTtmOUL8INiQvYG2830WDvRlIjvJhfVUAapDvChYMd4Qh3n/pIBsgpyRWlNBaO0UY%2BLmxgY9PeAM76qAIA/bU%2BwX60Dfh/G4X8f6qEkIAnOIDIFILxNIKk4ovynGoY7G09CICMKpIvfy99sZP1wfgz%2BD4FBKDxGQ1CIC7xSBuJQlhXBoi0Lge8GRTD5GnEUew1BzNQRjXHByVet4ADuhBkAIEMsjXmN80HwiQfaOqPZ4aLVPDEc8e17yLkqO%2BAgBCv5UEwPGGYmAhBIgABICkgtBWCrg7zeN8YiUOKxv6/3ASEPRfFj4IFPrlXh79%2BHEPASI4BoDwGQIOvTGGPwlIqT2A4ugOBiDEHeA2Rwyg5D7TcUiFYBhkAAGsz6/RiJqf2ONUIhEKbWGUFi4RUJoQ6WxeIBL2JMo4syt4CDPlccQdxnjIk%2BLdP4oJISOxQX8DBECWzokDzicQxsPxUnpOfrWV%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%2Bg/GexYJRXCYNfbwK8Skz2%2BxCMXK9zgsBnqLhWdDpAEPEBCPETAypMDgaML7Iwi6%2BAGGAAoA4eBMB6KYgRItDb%2BCCBEGIdgXBLj8fkEoNQZ7dBcH0BBkAphzA4bIpASYqBFkCGAwAWiYgAJSUj4pQiZN4rE0%2BCtpn9VwXE0wx1wOJNMsHCT2YwbrwinU0/wFghB3PFzYJpuImHiBTvI46rAymLIWH040TwEAHB9E8FIUgvhhh5AKBIGTcQEg2AEHFvQGWsgMDaClzooIItWCywwZovQXC1AkPUSL5XKtDFyB0CIXAZMFhaDl9rgxCstZAKCSYChq1zAkLm/NE7oPTpWAp/al8GCdLorgQgVk61cHGLwJtWhUxtvOKCO8oJQSRCZL2yIoIuD1ouJcPNHBx2kBYBIDQ86i0lunbOkA87NsttHRwSQE2XucA24uyY5GEh2HOEAA%3D%3D%3D)
```zig
export fn foo(x: @Vector(64, u8), y: @Vector(64, u8)) @Vector(64, u8) {
    return @select(u8, x < @as(@Vector(64, u8), @splat(0x80)),
        y,
 @as(@Vector(64, u8), @splat(0)),
    );
}
```

LLVM version: ([Godbolt](https://llvm.godbo.lt/#g:!((g:!((g:!((h:codeEditor,i:(filename:'1',fontScale:14,fontUsePx:'0',j:1,lang:llvm,selection:(endColumn:2,endLineNumber:6,positionColumn:2,positionLineNumber:6,selectionStartColumn:2,selectionStartLineNumber:6,startColumn:2,startLineNumber:6),source:'define+dso_local+%3C64+x+i8%3E+@foo(%3C64+x+i8%3E+%250,+%3C64+x+i8%3E+%251)+local_unnamed_addr+%7B%0AEntry:%0A++%25.inv+%3D+icmp+slt+%3C64+x+i8%3E+%250,+zeroinitializer%0A++%252+%3D+select+%3C64+x+i1%3E+%25.inv,+%3C64+x+i8%3E+zeroinitializer,+%3C64+x+i8%3E+%251%0A++ret+%3C64+x+i8%3E+%252%0A%7D'),l:'5',n:'0',o:'LLVM+IR+source+%231',t:'0')),k:50.91543156059285,l:'4',n:'0',o:'',s:0,t:'0'),(g:!((h:compiler,i:(compiler:llctrunk,filters:(b:'0',binary:'1',binaryObject:'1',commentOnly:'0',debugCalls:'1',demangle:'0',directives:'0',execute:'1',intel:'0',libraryCode:'0',trim:'1',verboseDemangling:'0'),flagsViewOpen:'1',fontScale:14,fontUsePx:'0',j:1,lang:llvm,libs:!(),options:'-O3+--mtriple%3Dx86_64-linux+-mcpu%3Dznver5',overrides:!(),selection:(endColumn:1,endLineNumber:1,positionColumn:1,positionLineNumber:1,selectionStartColumn:1,selectionStartLineNumber:1,startColumn:1,startLineNumber:1),source:1),l:'5',n:'0',o:'+llc+(trunk)+(Editor+%231)',t:'0')),k:49.08456843940715,l:'4',n:'0',o:'',s:0,t:'0')),l:'2',m:100,n:'0',o:'',t:'0')),version:4))
```llvm
define dso_local <64 x i8> @foo(<64 x i8> %0, <64 x i8> %1) local_unnamed_addr {
Entry:
  %.inv = icmp slt <64 x i8> %0, zeroinitializer
  %2 = select <64 x i1> %.inv, <64 x i8> zeroinitializer, <64 x i8> %1
  ret <64 x i8> %2
}
```

We used to get:

```asm
        vpmovb2m        k0, zmm0
 vpmovm2b        zmm0, k0
        vpandnq zmm0, zmm0, zmm1
```

Now we get:

```asm
        vpmovb2m        k0, zmm0
        knotq   k1, k0
 vmovdqu8        zmm0 {k1} {z}, zmm1
```

However, I thought it might be a good idea in some situations to use this technique:

```asm
 vpternlogd      zmm2, zmm2, zmm2, 255
        vpshufb zmm0, zmm2, zmm0
 vpandq  zmm0, zmm0, zmm1
```
</pre>
<img width="1" height="1" alt="" src="http://email.email.llvm.org/o/eJysOVmTorzav4a5sWYKIghezEXCJsoiIiLevMUSIbLKIuiv_wrtmeme7ZyvztvVJeTZnzxbUgRtS5IS468UhyhO-hT0XVo1Xw9BTuKgyT6FVXz_qlTNLKpiPMtJhmddSlpqDmcUh04kmalVHFZ5R3ESBYS06-oJSQGFAsqDJF-SCf0l756Q-YOaQ8vXkxQq6BpztjhCf9j6yBALtIuRDhXGFiMYbGURGo8BdQbkoT0onWGjO9wly01n-zK8tySk7SOURwEhuKlQuYfQhat6gMYNKv7e6dYJA-FtayhrfXGHZaIe1AU0NnUAD6Nv2HQ6oEyQ9hBy8QAve1WzoXRyIIxd5K5DVERz6b70KcABZDhoO0hJfhG1hdEZwd1JITkRmO7ne5ATulLu90qLKlMarlq7udZX-slX8x4FlHkoPFoCnaRzD2CdxQlnHPbkmqjVFV2O7gGmjOJDBCXXqQpNczTouenxCCG3zn20lVfgshi1x_0psueF0_myZPumic4JcqDUQlFJdhXUtMaSG5_4MHlIJx5VsijON4urEsJEMi4l2ENXlq0zY8HNU9TysTNsQ9Xoa9qrpZrd03abrjRcS6eVxmGwrk28Hp6kid4fxjrWkod5MjSOnY_ZOvU1qBV34Hd5YjNpa9du3Ap3T9ichOQQlY1wcTbX_VKK9I0rRTsRnyU5uhDUrprLei0fEjhXtQ0S-02SupkI5hRQZIZQQPE3Xm7g4goRIacT2ObYONDrQ1CnAfRFwqCz3evj_QYw8osqGYwsI7oZZYvogX19M4rNpTIT8DRd1_HQHPyQj3gKKEm4Pz3odehd5SiB7GXbyhoUG__kwrNtATm6LmQoZ1Bp_BPPjmbltMAkDQWUMSjbRmuhlTj6ypaW0aDCAup2rW0zf4CaKO_ldIXIYTR2_YZNmUpveWDL4ng_qApzWUIjGSURblIxsg-ZgVgRYnVtiP15FKQC7cp0uIni-mn0Fl6R52ZyYewhXGVXZb2LBctnLkQfXOLt9BD6j2FHPN2_kJ32FiRv18VEXMv8Ba-9PQpE9-yfDHYpFvLwgLYTewd2V_XkSQ2cA3wMzR5q6LmWk0NRWpECjmZk3ufHSBr1w8EZPZQelcpLYuNxzNnD0qlkmwKKfhehaTqc5stkO6L4cRTJAwZQjKHixefHU6aqWcSUbpawTEU7SUV56SwT0pCqZovNOYE49Sxu5UZbOLhrQ6aAshXm-Xr0_IuSR4_m3mmsDJXT4AZJMDeD7nrciVcJ9eoQ3McbvGviolQEb1AF1TmtWFN2ub2BPHFvoIILbrY6PIRe1q679abde5p1I0HTW6Hb0FNzagd7mVNAMWNFSSrX1cvqafbIHI74kivNzuE9qwfOvSep_USZ3rBPtZS-mhv6ul8d1Xl2u8UnCQLJNXn6fFrKtvaiXGwR7VSBd2s2195aEKsGKwooFWcu2hE_mkBfj-rm7Pa8X8nFg7sflZih52G8BIO1vDBCp2NXfGz8NDAukaO2ah-lZWka2aJpzNI-8mulfoxRflPkR0HMfaL0jzSKWk8C5mjuDqTt2Ouw1g3kXIzTCaVpoKr7k9E3Ia0EV2Q3xb0XYiOC8Ip2gWLDhGyCpXoLA7Bl-dvGwrflUaW1NelK2oMpEf1gcM-VRg7Z4w5SP6KPpZazQlNMFeKF5-bp-py_PGqBp3X25lBAyS7CZtHMvSZuBsBHYXkM100yD_0wA55z6q6eXzQr92iNI7FH3xLl0wOA06nwrMY_CwZ0V1cRaIexUfddYbm6oJnEvvkqEOa0J912uXa5rdPzwYVBLd3E1Ddi1k7nJQWUWkNtUt93Xm6iwKLdVz_XizHxl1sMDX5xhdo0rEL3iRmOC1o6pxRQVPYonBdXOdNgaWmSpmj6aGqbjK1u91KtfF6ll6ImGptau53vy2V72jLDOXklvsQqaCONqs2ImsiPDurXdp4eUUVoPcGCuttLnFrKLh4Y9DDt3eW4QvcD7lgo9SnKoCYb7eVYmAK9Goh9Dqzr9sQG-mEryZGAGf6uZ1frqQkmSLxxrjxsVdUvYIq0BCJNzJIOeWKT8A9sCj5xrc14W0yzCDrydndWLqymbJv8mPLLp5iVvIWOxqJKGlRbs257Vd0OuXbdA8j2iYWIJK8wBLvhnnASv49covgozSBU28ckd0fW1zOwTFdL5U3oqa5C2J27ruyFN2IN6WBtVGx771hR2uZRZMdjedGyVzDiLVutNcca7aMgIVn0HlUmPUhkj-12dMvaOjfe4Unq7cXVuNaO2TVRpGDMaa1h3NqiN_lhW5mJVy_3wd20gj0dj7zj8LF527Dbeg07--Sqx4tjQ0Yjl4LTz85IX06rvamv_EshkXKlm15AX0YKKGKV8Zpo2_56vbbz1VYMovLUOkgR145LzPUCKvC07Y_JyB2XSBFN7Glkt9ubp_OWb6Qjh5lNpltXX-zrelBzcx3gtqtX-8pbbhc-4S37vvMu2oiN66HJWf_eNqtNpdQjP7rIR-yQn_JcksWbtnJsi1VFdFi2njnyqYqCrCo75CWXecgfbJlkxo4tncBQKxYlkt8QZ0itJnL8hnMCcy_poXEVJXZI2LXhJSVEV0EW0KDbNXLFSJqrvifQ4ynld82KrJIaDo1SP07GvtYgumZms_USWKIq7BhJlOfSuJkGtF2iB1FaWh-MboUwymxaA_c4G1hxEO2tIGgc2qCmIoav9cLBygWZt2SDyNAm-07b5qdkhOUlUliE75U0FFqq0ka0T6RwP7ayLI8rwCwcxl-FBpTwPLtr805TEiVJ00QiahigGyRr5zXKkqlc8eivd0fRN8_hsBGc7PEa_6NoHDfLR9Ki8qqnXizVUN7KSNzKe3ivDSkJDJ3XBrJ4VZOqQlhBFiMDLTZ-stM6KXxiRBHJqhYnR6RfhHMmV6Z94mMUrWiEMlinD8iGWg0d_4qUTFThAD3iJ3DtuBe2tsnJZBv5dSgUu7pcHoajTA8jM1hr02hX4h74Q9gMpHSnyTQoSYrmW-Xhr-teK1YE7W8au2jgvdA1b0Wz9H6Q4QotZUHR3OSWpikHN0hT95EtJwDKK-Vmq16bGFIg5o-q0rTOE-_DcKpu9lFkYLZ1HZ07bjpJuSNa1I7wZChpIOXLJhnFtjvBjej4YnplHjDTi2lGyny13dcerCmgBLmgirFeNYmdHLIFE61UfVh3XuqO3c3aiJZQrW1nJ550cNcqrZeYql9HW3OFRpAhH2mSLSwInfdlaGVQ4M2261a7wbFlcOwjCNj-7nOqnIKVJUNIAW4uvf9ZUjSkFvTr_0ESioZ4rKumm53L2bmqKCCMz_sJSx9w1FUNBYQFSwFx1gsTNxBn97_il39CzSgeUTSczWazBnd9U06ELc5x1FFAmEjE2Tij5uIED1oKCH-xYWKt82DipEeBfmmmgPimYPq7vy3_n9J-FjUt5pPhFC-937vpnYa6fjBmN9y0pCqf2wIEikN_udXl-a346VqXPJHMxAqEPy9Sag6ne6Qck6cTInlihTPJcRkU-LniGQrwFBDPVdk5UZBPUIZ9A7gt3o4vMvpFdpnQFBDzoJx0TcZRQHwF5eURBQRcxmKV98W0BBQQcRnrpMRmX4S4oeZwQQGxrloycXwg_Ab8hfq7AqcLmu4Dz0fUr5y_MvyObopfW_VN9LYrMT6TElMAxW31T15FQU6B6eg-F6dMQCMFEBGmtTzBWfpVCH8kABzg6ClF_iJkomGelqCnwn_6copS_E8Qx82LgJ9-aCiXXXN_2snR8Il5cX8h5e1NgzTJjoqaAqid0ubvat9Me-CmIiXpSJCTB25-Fg_eyf5Whj_LZT7IfRn0N69_UfnfbNF3sxr8H10Db-QcLz0zeAp0_oox90rp8kOCV6_VVKYUQNpu8vWVFy-B87d66d5zvTWAjJpDjv6yZDh2znALmlsCgfuhj_2Lvtdiqnr6N8LF35d2UZMcvyvs75CpMKOu6ctsKmSSd7h5NRQh_KA8JGXwlknf-sALZIWXKbzvEVFVFLjsrDK_f5AR47BPxCDP2w_kMS6CMsnxR1rSTLV6w-0HMB5x1Hcf-xEpO5x_oMpJ2ATNXazij0K7hhQfWG-4CasWSy8LSJn8vJvnPEjaA8GDVePy3-uCOQnbd0GaNFX11JnevP1szSmAPn8uuobUOX6W0igs_lmwn3NS9lPyfi6iun8iHuUNN28ZWt1w05AY_yz9L22X-U3bZX7Xdpk_tV3mz233V9SvnL8y_I7uQ9tl_uvqnFpkHj0rUnhL8-Vr9W3Wfa_V5d_LlV1-oQWWWwjsfMnSPPOvlOs7L8CLckpQhqb_Lu53Yn6cFNg32LsTxTPvaPiaVbPvk2o6Ei3Y2TgjAjWXZz-m00fwq-3_TPyaQbNfJ9Dbaez77JkOO9Srxc-ouTSbps2szbtfBT7V_Nzo39jBk_eVTD84mTfOt_nxk8hfZ8bvnJgUNPg35oA_Hc08POtbHM-6apbg7uXje6qgLd6dFm91Ud1CUHxbZy83i2KS9sIWIPyGfcKBOFG9FxGUcXn9jnz3ZH41z6yG2YD_d9O-Acuqu05P5oddt6K6xddeeG_1FPeMoXhpenlMG_dHC1fVgG-vgGizLq36JO1mpJsVZHoJ8SyYJVUVz0iMgxkpZ21V4FlLuj54dslp4_v29cVj1uEoLcm1x3909lZ3uCnzKom_GwvebPvwBBz3YW_atD-H7_cafAxcUMbX2X-Myaf46zxezpfBJ_yV4TlWYDh2wX9Kv8YRCHjMgpiN2CW_CIMzZqNzwOAYLOiQFj6Rr4AGHC0wNC2wLOC_LALMC-DMxzigF2wQUyyNi4DkX55H_6pJPpG27fFXhgNLmv6UByHO2-cXJABKPMyeWAoAipM-NV8nps9hn7QUS-ek7dofYjrS5c9PT_Bw_MwxE8NMrMqWxLiZ9S0pkxm1oN926HUB-nFnUpS3u884PRf0bEhx-Va5E2dVTsyv-9jzhrWgP_VN_vXjbSYhXdqHX6KqeLvavD0-1031PHIA5elOSwHlzd_bV_B_AQAA__8QShrl">