<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/151691>151691</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [SPIR-V][HLSL] Fix lowering of poison in shufflevector when swizzle are used
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            backend:SPIR-V
      </td>
    </tr>

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

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

<pre>
    Given the following sample
```hlsl
// RUN: %clang --driver-mode=dxc %s -T ps_6_8 -E main -O3 -spirv

/* Copyright (c) 2025, Sascha Willems
 *
 * SPDX-License-Identifier: Apache-2.0
 *
 * Licensed under the Apache License, Version 2.0 the "License";
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

struct VSOutput
{
    float4 Position : SV_POSITION;
 [[vk::location(0)]] float3 Color : COLOR0;
};

float4 main(VSOutput input) : SV_TARGET
{
    return float4(input.Color, 1.0);
}
```

The generated IR is:
```llvm
  %0 = load <3 x float>, ptr addrspace(7) @COLOR0, align 16
  %1 = shufflevector <3 x float> %0, <3 x float> poison, <4 x i32> <i32 0, i32 1, i32 2, i32 poison>
  %vecinit78.i = insertelement <4 x float> %1, float 1.000000e+00, i64 3
  store <4 x float> %vecinit78.i, ptr addrspace(8) @SV_TARGET0, align 16
```

Issue is the poison being used in the shufflevector index.
This is lowered as a `-1` in the backend, which causes a validation error.
Emitting any other valid index like `0` should be fine since the value is overriden just after.
</pre>
<img width="1" height="1" alt="" src="http://email.email.llvm.org/o/eJxsVl9z4r4O_TTmRQOTOPx94IEC_S2zndIBtnv3acckCtGusXNtB9r99Hdkkt62v2U6g5tI50hHsoTynk4GcS5Gd0LKr4imCV5IKUarnmpCZd28fdg72uJ1_g9d0ECoEEqrtb2SOYFX51qjSBZinNz-Ku01_y_vhbyH3bdHkS1AyFGulTlBv184uqDrn22BIlsVLzm_9NA_QO1_jn9Oob-GsyID_W0GfV-TuzBci7iApa1fHZ2qAEJOcyFnIBM5EnIJe-XzSsF30hrPXiRMu2i_YP-0-k__gXI0HvubAk2gktBxcIta5RX25SD55NOaF9CYAl3M_GbbvWHWZ3SerAE5SKKFkPLtrRTZXQf2ahs4q1cwNkDjEUJFHkrSCPiSYx2ADOT2XGtSJke4UqgiXgs26HB-tDj2GFglBbmtX8GW741BhU-p8KcKoRZZW5nr9TpQMZmBdSch7_XN1Qt5_7BZrh_3678o8s1o9B4c_rchhwUcX0HVtaZcHTWCVlewDtTJIRYQLKd0dRTInFgpb8twVQ47sIJ8cHRswgeFuxTIfzCwBpRhcRd72OyFlHC32PNh2cF93xy-bL8d4Ptit1s8HjbrPWx3sNw-rjaHzfZxD9t7WDz-gK-bxxWHgxQqdIAvteOcrANi9bF4k3qP-CGk0t5C9DXmVFIO3NKNOiGc7AWd4QtRozuT547woEzRQWk6U1AhPv5Xrh0hVya2ug-uyQM877dNqBuupZjERgKAUlsVhvBkPTEccAfvn38-bfcxza7jRndidHf5zfXOFtrmkVvIaSLkTIxWYrS6IWWwtNq6CLPcPmx3yQ1BTFbtIVm0lHwrhZx2UQEZjk3OuhAOi90_68OHYB2Gxpk2ZiGn0WUQGbkE6SCG80b4bozcmA8VwgkNOsU9sNkBec7onZ3Wl3MkE3KUgMhWoK0qQGTLDF5uxCJbM1kdHKiicL5WOQo5ncTQh0mbtVyC0nQykI47vDTi-aopS40XzEPU6QNwpGXfz89rS54Fj2-G8AKUyWifLSmTEH34kHYH2R1az2zdhXHBnAyFyXRAMSAyHl1AjWc0oYN_H1DEjA9Y4fhBIe-SG-l4CFmE9sE6_Jv_O8K_CTdthXsr-WfxPhVx430T7zO3_C07OCJfloaHK912ykeZyRT4MogdQJ59tb0iTxzlQYEYJ_1UjJPO96jy32gKDuNaUV5BrhqPbHlRmorY-4DOWceQ6zMFnkmgzCvYOASi2Y0UNP1GZuAEwFe20QUcEUoyCJ54NjPlRelbUnzzHRVo4FfjA6gyoBv0inlWzLKZ6uE8nYyGyUimMu1V8-kkGeUZ5iWOhuNZecwmOFOTXGGWpOUoK3s053WWTJM0lUOZJINifCymwywvMMlSpVIxTPCsSA-483l294j1naejdDxLe1odUft2p3e6ZIv902bXf26Xu5uzb__YnLwYJpp88P9HCxR0_E3QuvCsuPvysH_gkXFPL7dKsHy27KpJ5lP5rhUa8Ff680cjKIex0r3G6TkvIf-2hU4UquY4yO2ZNxBf5dtXv3b2F-ZByPuYHW-lNsHLXP4vAAD__xn-rRE">