[llvm] [LLVM][MC][DecoderEmitter] Add support to specialize decoder per bitwidth (PR #154865)

[Rahul Joshi via llvm-commits]

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@@ -700,6 +700,12 @@ static constexpr DecoderListEntry DecoderList32[]{
     {DecoderTableZdinxRV32Only32, {}, "RV32-only Zdinx (Double in Integer)"},
 };
 
+// Define bitwidths for various types used to instantiate the decoder.
+template <> static constexpr uint32_t llvm::MCD::InsnBitWidth<uint16_t> = 16;
+template <> static constexpr uint32_t llvm::MCD::InsnBitWidth<uint32_t> = 32;
+// Use uint64_t to represent 48 bit instructions.
+template <> static constexpr uint32_t llvm::MCD::InsnBitWidth<uint64_t> = 48;
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jurahul wrote:

@jrtc27 The decoder know the number of bits, but not the actual C++ type to be used for that bitwidth (it generates templated code and backends are free to use whatever compatible types they want to use). `InsnBitWidth` is a way for the particular target to communicate this intent to the decoder generated code.

https://github.com/llvm/llvm-project/pull/154865