Imported Upstream version 5.18.0.205

Former-commit-id: 7f59f7e792705db773f1caecdaa823092f4e2927

external/llvm/test/Bitcode/mdnodes-distinct-nodes-break-cycles.ll

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+; RUN: llvm-as <%s -bitcode-mdindex-threshold=0 | llvm-bcanalyzer -dump | FileCheck %s
+; Check that distinct nodes break uniquing cycles, so that uniqued subgraphs
+; are always in post-order.
+;
+; It may not be immediately obvious why this is an interesting graph.  There
+; are three nodes in a cycle, and one of them (!1) is distinct.  Because the
+; entry point is !2, a naive post-order traversal would give !3, !1, !2; but
+; this means when !3 is parsed the reader will need a forward reference for !2.
+; Forward references for uniqued node operands are expensive, whereas they're
+; cheap for distinct node operands.  If the distinct node is emitted first, the
+; uniqued nodes don't need any forward references at all.
+
+; Nodes in this testcase are numbered to match how they are referenced in
+; bitcode.  !3 is referenced as opN=3.
+
+; CHECK:       <DISTINCT_NODE op0=3/>
+!1 = distinct !{!3}
+
+; CHECK-NEXT:  <NODE op0=1/>
+!2 = !{!1}
+
+; CHECK-NEXT:  <NODE op0=2/>
+!3 = !{!2}
+
+; Before the named records we emit the index containing the position of the
+; previously emitted records
+; CHECK-NEXT:   <INDEX {{.*}} (offset match)
+
+; Note: named metadata nodes are not cannot reference null so their operands
+; are numbered off-by-one.
+; CHECK-NEXT:  <NAME
+; CHECK-NEXT:  <NAMED_NODE op0=1/>
+!named = !{!2}