[llvm] [CodeGen] Check for no VN before def to catch potential split components (PR #191141)

[via llvm-commits]

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@@ -561,6 +561,8 @@ bool LiveIntervals::computeDeadValues(LiveInterval &LI,
       }
     }
 
+    if (!VNI->isPHIDef() && I != LI.begin() && !LI.getVNInfoBefore(VNI->def))
+      MayHaveSplitComponents = true;
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sc-clulzze wrote:

I agree that the cleanest way would be to always run splitSeparateComponents, if it does not cause compile time slowdown we should go for it instead. 
I dont think I can merge it with the code below, because it hadles case if defining instruction is dead(

https://github.com/llvm/llvm-project/pull/191141