diff options
Diffstat (limited to 'llvm/test/Bitcode/mdnodes-distinct-nodes-break-cycles.ll')
| -rw-r--r-- | llvm/test/Bitcode/mdnodes-distinct-nodes-break-cycles.ll | 29 |
1 files changed, 29 insertions, 0 deletions
diff --git a/llvm/test/Bitcode/mdnodes-distinct-nodes-break-cycles.ll b/llvm/test/Bitcode/mdnodes-distinct-nodes-break-cycles.ll new file mode 100644 index 00000000000..51701d10c03 --- /dev/null +++ b/llvm/test/Bitcode/mdnodes-distinct-nodes-break-cycles.ll @@ -0,0 +1,29 @@ +; RUN: llvm-as <%s | 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} + +; 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} |
