[clang] [compiler-rt] [llvm] Reland "[X86][AVX10.2] Support AVX10.2 option and VMPSADBW/VADDP[D,H,S] new instructions (#101452)" (PR #101616)

[Shengchen Kan via cfe-commits]

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@@ -223,6 +227,10 @@ InstructionContext RecognizableInstr::insnContext() const {
           insnContext = EVEX_KB_U(IC_EVEX_XD);
         else if (OpPrefix == X86Local::PS)
           insnContext = EVEX_KB_U(IC_EVEX);
+        else {
+          errs() << "Instruction does not use a prefix: " << Name << "\n";
+          llvm_unreachable("Invalid prefix");
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KanRobert wrote:

I meant there is always a default prefix opcode `PS` for EVEX prefix, so `does not use a prefix` is misleading.

Yes, I suggest merging the `errs() << ` into `llvm_unreachable`. 

https://github.com/llvm/llvm-project/pull/101616