[llvm] MC: Store MCRelaxableFragment MCInst out-of-line (PR #147229)

[Fangrui Song via llvm-commits]

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@@ -431,16 +428,38 @@ class MCDataFragment : public MCEncodedFragment {
 ///
 class MCRelaxableFragment : public MCEncodedFragment {
   /// The instruction this is a fragment for.
-  MCInst Inst;
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MaskRay wrote:

You are right. I take back my previous comment.. Updated the description

> Unfortunately, we also have to encode MCInst::Flags to support the EVEX prefix, e.g. `{evex} xorw $foo, %ax`.

I only noticed the case after adding the `getFlags() == 0` assertion... The #78545 case should probably switch to llvm-objdump -dr

https://github.com/llvm/llvm-project/pull/147229