<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/144573>144573</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [DirectX] Accessing a cbuffer array with a dynamic index hits an assertion error or generates incorrect code
        </td>
    </tr>

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

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

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

<pre>
    Compiling the following shader results in an assertion error (if compiled with assertions enabled) or incorrect code generated (if no assertions are enabled) when compiled under clang: https://godbolt.org/z/5Yszfrx1K

`clang-dxc -E CSMain -T cs_6_2 -enable-16bit-types`

```hlsl
RWStructuredBuffer<uint32_t> output;
cbuffer Constants {
  uint32_t v[2];
}
[numthreads(1, 1, 1)] 
void CSMain(uint3 Tid : SV_DispatchThreadID) {
  output[Tid.x] = v[Tid.x];
}
```
```
clang-dxc: /workspace/llvm-project/llvm/lib/Target/DirectX/DXILCBufferAccess.cpp:69: size_t getOffsetForCBufferGEP(GEPOperator *, GlobalVariable *, const DataLayout &): Assertion `Success && "Offsets into cbuffer globals must be constant"' failed.
```
https://github.com/llvm/llvm-project/blob/9e0186d925f0c375a627866c59394f25c22eb3ff/llvm/lib/Target/DirectX/DXILCBufferAccess.cpp#L69

The generated DXIL has the following incorrect cbuffer load instruction which always loads from index 0 instead of the thread id.
```
  %3 = call i32 @dx.op.threadId.i32(i32 93, i32 0) #2
  %4 = call %dx.types.CBufRet.i32 @dx.op.cbufferLoadLegacy.i32(i32 59, %dx.types.Handle %2, i32 0) #1, !dbg !101
```

The same shader will successfully compile and validate under dxc.
</pre>
<img width="1" height="1" alt="" src="http://email.email.llvm.org/o/eJycVU1v4zYT_jX0ZWBBGpmydfDBH_G-wZtiFxtjuz0FFElZbGnSIKnYzq8vqI_E8fbSAoI0IueLM88zZN6rg5FySeia0O2EtaGxbvnIbSOFs2ZSWXFdbuzxpLQyBwiNhNpqbc_xzzdMSAdO-lYHD8oAM8C8ly4oa0A6Zx0QXKgaeOdCCjir0HzoeJCGVVoKgiVYB8pw65zkAbgVEg7SSMeCFIMXY29NmZO35udGmo84rYmpcc3MgeQraEI4eZKvCO4I7g5WVFaHxLoDwd0bwR39w7_V7pL9n6Sr-BRpZzoVFw7TB9g8_8aUgekeuH8pXhCmfeBpVlQqTMP1JD0p0nfj_mm01yRdff_9ObiWh9ZJsW7rWjqSb1plQo4vgeQPYNtwagPJ1yRd8arTgI01PjATPJB5XAcYLeCV0DUSuu0NyHwb33Rt2mNonGTCE1xkBDcwvkpCt0DS1atVYjgKwUXnD_ZKQCzQ84-XrfInFniz77w8bmNRx-BDinS9VyK5dP7ybZfJuPApm7ECd_J7TWMnNkhWKcHd2bq__IlxSXCn9etxenL2T8nD8Bs_qiK42zN3kHF1qyJCfkbp5-PTpi_pinPpfcJPJ5KvivI9gFdv8iX08kGGr3XtZdhZN5h9efhGcPHl4dvXU0SadWNaK4KbXv6ibcX0D-ZU7Piv-zx2qhe3LLAndrVtGNWKWP0xl9WI3WG3SJ_bLu0b7WKUsU912FMm2CFcD5DhRF1ug86xHfOo5E1qzASCSHDer9Us8iO568wdP1Ro2irh9njThM-tqbSNTSllmi0KUSKtU57PKStwvigKTsu8nNVIOaKs8rr-z83E_Kkoe17tm9uJENWhYf5uJt1MkIFJ2jIByviOg3EunRvFG2D6zK6-2_VQO3sEZYS8QNrpSibA1p3vnlSgfqkZAEGad0TgTGtQOQKZpeKS2FPSWz2KROUYh1eOUOaRj1FKO2phjqOX2YcXglRckm6iJLEc32VIPnkezvVkmXiSB8avNyFoGUPcuvgfM0LLuIT30bNeNxPVIX6yNLunbl9zz45ynPVnpTX4HrV1q_V1nLjAjIBXppVgQQ7TV1x4MhHLXJR5ySZymc1pmi1wUdBJs-QZ5bTOWV3X2QzL2aJgqZRIOcN5Xs_4RC0xRZoW2Tyb0xnSpMA6n_OUVQWvC4GczFJ5ZEonEVlxlk-U961cZrMZnecTzSqpfXezIRp5hm43UoFuJ27Z4blqD57MUq188B9uggq6uxJHcNIt9JCMCGPvyGLOsetwo4G4GnZUfEBRo4L_p9vQuncI-7vbbtI6vfzXPOwO5QnuhlO_LvHvAAAA__9HYm85">