[llvm-bugs] [Bug 43271] New: TableGen+ninja restat optimization doesn't seem to fire for me

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=43271

            Bug ID: 43271
           Summary: TableGen+ninja restat optimization doesn't seem to
                    fire for me
           Product: Build scripts
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: cmake
          Assignee: nicolasweber at gmx.de
          Reporter: rnk at google.com
                CC: llvm-bugs at lists.llvm.org

I noticed that after modifying llvm/lib/Support/VirtualFileSystem.cpp, all
compilation actions are re-run, despite the fact that the tablegen output does
not change. The expected behavior is that tablegen re-runs, all headers are the
same, and then we just relink clang.

This was the final ninja line showing that all CXX actions were run, rather
than being discarded from the build graph by restat:
[1 processes, 2234/2234 @ 18.2/s : 122.601s ] Linking CXX executable
bin\clang.exe

IIRC Nico changed this in r349624.

I'll debug it more tomorrow, filing now before I forget.

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