[llvm] [GVN] use `AssertingVH` for leaders to improve compilation time (PR #175870)

[Antonio Frighetto via llvm-commits]

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@@ -819,33 +818,27 @@ void GVNPass::LeaderMap::erase(uint32_t N, Instruction *I,
     return;
 
   if (Prev) {
+    // Non-head node: unlink and destroy
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antoniofrighetto wrote:

Comments should end with dot (here and elsewhere).

https://github.com/llvm/llvm-project/pull/175870