[llvm] [LLVM][MDL] First integration of MDL with LLVM (PR #78002)

[Aart Bik via llvm-commits]

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+# MPACT Microarchitecture Description Language
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+Reid Tatge          [tatge at google.com](mailto:tatge at google.com)
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+## **Goals for a Machine Description Language**
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+Modern processors are complex: multiple execution pipelines, dynamically dispatched, out-of-order execution, register renaming, forwarding networks, and (often) undocumented micro-operations. Instruction behaviors, including micro-operations, often can’t be _statically_ modeled in an accurate way, but only _statistically_ modeled. In these cases, the compiler’s model of a microarchitecture (Schedules and Itineraries in LLVM) is effectively closer to a heuristic than a formal model. And this works quite well for general purpose microprocessors.
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+However, modern accelerators have different and/or additional dimensions of complexity: VLIW instruction issue, unprotected pipelines, tensor/vector ALUs, software-managed memory hierarchies. And it's more critical that compilers can precisely model the details of that complexity. Currently, LLVM’s Schedules and Itineraries aren’t adequate for directly modeling many accelerator architectural features.
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+So we have several goals:
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+
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aartbik wrote:

as for the other doc, avoid too much vertical space (when it does not matter for formatting)

https://github.com/llvm/llvm-project/pull/78002