[Issue 23990] New: constant folding of integer casts not always happening in front end

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=23990

          Issue ID: 23990
           Summary: constant folding of integer casts not always happening
                    in front end
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: bugzilla at digitalmars.com

It gets deferred until conversion to the intermediate code, unless CTFE is also
run. This causes:

1. some inconsistencies in the expressions after semantic analysis
2. some high level optimizations to be missed
3. constant folding passes to get unnecessarily re-run

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