[clang] [llvm] [HLSL][DXIL][SPIRV] Create llvm dot intrinsic and use for HLSL (PR #102872)

[Farzon Lotfi via cfe-commits]

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@@ -1366,6 +1383,67 @@ bool SPIRVInstructionSelector::selectRsqrt(Register ResVReg,
       .constrainAllUses(TII, TRI, RBI);
 }
 
+// Since there is no integer dot implementation, expand by piecewise multiplying
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farzonl wrote:

actually I see a `OpSDot`, `OpUDot`, and `OpSUDot` (for mixes signedness)  in the [spec](https://registry.khronos.org/SPIR-V/specs/unified1/SPIRV.html). Maybe we just don't use these in DXC's spirv generation. I'm fine with sticking with what DXC does we should at least mark the comment accordingly.

https://github.com/llvm/llvm-project/pull/102872