[clang] [HLSL] Implement the SV_InstanceID semantic (PR #221091)

[Gregory Roth via cfe-commits]

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+// RUN: %clang_cc1 -triple dxil-pc-shadermodel6.3-pixel -finclude-default-header -x hlsl -verify -o - %s
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pow2clk wrote:

Mostly disregard, but you might consider adding a CS test too.

https://github.com/llvm/llvm-project/pull/221091