[llvm] [NewGVN] Prevent cyclic reference when building phiofops (PR #69418)

[Nikita Popov via llvm-commits]

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@@ -3812,9 +3812,20 @@ Value *NewGVN::findPHIOfOpsLeader(const Expression *E,
     auto *MemberInst = dyn_cast<Instruction>(Member);
     if (MemberInst == OrigInst)
       continue;
+
     // Anything that isn't an instruction is always available.
     if (!MemberInst)
       return Member;
+
+    // Prevent cyclic reference, such as:
+    // %a = add i64 %phi, 1
+    // %foundinst = add i64 %a, 1
+    // =>
+    // %phiofops = phi i64 [1, %BB1], [%foundinst, %BB2]
+    // %foundinst = add i64 %phiofops, 1
+    if (llvm::find(MemberInst->operands(), OrigInst) != MemberInst->op_end())
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nikic wrote:

is_contained

https://github.com/llvm/llvm-project/pull/69418