[llvm] [AMDGPU] Only try DecoderTables for the current subtarget. NFCI. (PR #82992)

[Matt Arsenault via llvm-commits]

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@@ -507,27 +510,32 @@ DecodeStatus AMDGPUDisassembler::getInstruction(MCInst &MI, uint64_t &Size,
           tryDecodeInst(DecoderTableGFX90A64, MI, QW, Address, CS))
         break;
 
-      if (tryDecodeInst(DecoderTableGFX864, MI, QW, Address, CS))
+      if ((isVI() || isGFX9()) &&
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arsenm wrote:

I think it would be better to have a common table for all sub targets with a shared encoding. That looks more like normal cpu targets, where you can emit instructions that will just fault on unsupported CPUs. Really we probably should be using different top level targets for each major encoding change 

https://github.com/llvm/llvm-project/pull/82992