[Issue 20177] New: Streamline cycle detection code due to no more duplicates

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=20177

          Issue ID: 20177
           Summary: Streamline cycle detection code due to no more
                    duplicates
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Keywords: performance
          Severity: enhancement
          Priority: P1
         Component: druntime
          Assignee: schveiguy at yahoo.com
          Reporter: schveiguy at yahoo.com

Module cycle detection code currently deduplicates any imported modules. See
issue 16208 for an explanation.

However, this was recently fixed (see issue 20037). I can probably avoid
allocation of the edges arrays and just use the already-existing moduleinfo
data to do cycle detection to streamline the code.

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