[llvm-bugs] [Bug 50294] New: LLVM12 PCH leads to 2x slower compilation times

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=50294

            Bug ID: 50294
           Summary: LLVM12 PCH leads to 2x slower compilation times
           Product: clang
           Version: 12.0
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: normal
          Priority: P
         Component: -New Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: diaconitagabriel at gmail.com
                CC: htmldeveloper at gmail.com, llvm-bugs at lists.llvm.org,
                    neeilans at live.com, richard-llvm at metafoo.co.uk

Starting with LLVM12, we are getting a 1.5x - 2x performance hit if we compile
our projects using PCH, compared to without PCH with LLVM 12. Exactly the
opposite of what one would expect by using precompiled headers.

Compared to LLVM 11, with PCH enabled, we are observing a penalty of 3-4x.

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