Scott Linder 47e3a5ca06 [DebugInfo] Enforce implicit constraints on distinct MDNodes ... Add UNIQUED and DISTINCT properties in Metadata.def and use them to implement restrictions on the `distinct` property of MDNodes: * DIExpression can currently be parsed from IR or read from bitcode as `distinct`, but this property is silently dropped when printing to IR. This causes accepted IR to fail to round-trip. As DIExpression appears inline at each use in the canonical form of IR, it cannot actually be `distinct` anyway, as there is no syntax to describe it. * Similarly, DIArgList is conceptually always uniqued. It is currently restricted to only appearing in contexts where there is no syntax for `distinct`, but for consistency it is treated equivalently to DIExpression in this patch. * DICompileUnit is already restricted to always being `distinct`, but along with adding general support for the inverse restriction I went ahead and described this in Metadata.def and updated the parser to be general. Future nodes which have this restriction can share this support. The new UNIQUED property applies to DIExpression and DIArgList, and forbids them to be `distinct`. It also implies they are canonically printed inline at each use, rather than via MDNode ID. The new DISTINCT property applies to DICompileUnit, and requires it to be `distinct`. A potential alternative change is to forbid the non-inline syntax for DIExpression entirely, as is done with DIArgList implicitly by requiring it appear in the context of a function. For example, we would forbid: !named = !{!0} !0 = !DIExpression() Instead we would only accept the equivalent inlined version: !named = !{!DIExpression()} This essentially removes the ability to create a `distinct` DIExpression by construction, as there is no syntax for `distinct` inline. If this patch is accepted as-is, the result would be that the non-canonical version is accepted, but the following would be an error and produce a diagnostic: !named = !{!0} ; error: 'distinct' not allowed for !DIExpression() !0 = distinct !DIExpression() Also update some documentation to consistently use the inline syntax for DIExpression, and to describe the restrictions on `distinct` for nodes where applicable. Reviewed By: StephenTozer, t-tye Differential Revision: https://reviews.llvm.org/D104827		2021-06-28 21:20:04 +00:00
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Reader	[DebugInfo] Enforce implicit constraints on distinct MDNodes	2021-06-28 21:20:04 +00:00
Writer	[DebugInfo] Enforce implicit constraints on distinct MDNodes	2021-06-28 21:20:04 +00:00
CMakeLists.txt