[llvm] [CodeGen][Tablegen] Fix uninitialized var and shift overflow. (PR #84896)

[Phoebe Wang via llvm-commits]

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@@ -935,7 +935,7 @@ void DecoderEmitter::emitTable(formatted_raw_ostream &OS, DecoderTable &Table,
       unsigned Shift = 0;
       do {
         OS << ", " << (unsigned)*I;
-        Value += (*I & 0x7f) << Shift;
+        Value += ((uint64_t)(*I & 0x7f)) << Shift;
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phoebewang wrote:

Sorry, I think the (uint64_t) in needed, because `Value` is uint64_t and `Shift` may larger than 32.

https://github.com/llvm/llvm-project/pull/84896