[llvm] [RISCV] Preserve tail agnostic policy in foldVMV_V_V (PR #105788)

[Philip Reames via llvm-commits]

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@@ -498,10 +500,12 @@ bool RISCVVectorPeephole::foldVMV_V_V(MachineInstr &MI) {
                                               *Src->getParent()->getParent()));
   }
 
-  // Use a conservative tu,mu policy, RISCVInsertVSETVLI will relax it if
-  // passthru is undef.
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preames wrote:

I found this thread very confusing, so let me comment that I talked to Luke and the original comment never held.  We thought it did, but we made a mistake in our reasoning.  The missed optimization was simply never visible in practice without the follow up changes.

https://github.com/llvm/llvm-project/pull/105788