[llvm-bugs] [Bug 28222] New: llvm-tblgen is still too slow in the default debug build configuration

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https://llvm.org/bugs/show_bug.cgi?id=28222

            Bug ID: 28222
           Summary: llvm-tblgen is still too slow in the default debug
                    build configuration
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: normal
          Priority: P
         Component: Target Description Classes
          Assignee: unassignedbugs at nondot.org
          Reporter: rnk at google.com
                CC: cbieneman at apple.com, llvm-bugs at lists.llvm.org
    Classification: Unclassified

I'm filing this bug because I bothered to build LLVM in debug mode on Windows,
and it's ridiculously slow. This has been a persistent problem across LLVM's
entire history, and many people have attempted to solve it, but it still
persists. Currently we have LLVM_OPTIMIZED_TABLEGEN, but this is off by default
and doesn't play well with ninja.

I think we need should solve this by building lib/Support in both release and
debug configurations when we detect that the user is building in a debug
configuration. The release version of support would be linked into llvm-tblgen.
We would also optimize the code in lib/TableGen, which changes infrequently and
doesn't need to be debugged very often. We would also disable things like debug
iterator checks to make these libraries faster.

We'd probably disable this complexity in an "expensive checks" build. We also
don't want to do this when the user is already doing a release build, since it
increases the total compilation work.

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