[flang-dev] Build Time Comparision

David Truby via flang-dev flang-dev at lists.llvm.org
Thu Jul 30 01:28:35 PDT 2020

Hi Michael,

Thanks for these numbers, this data is useful and seems to match what I
see on Linux.
To add another observation: the truly pathological linker case only
comes up in Debug builds rather than Release builds, which is when I
start to see peak linker resident usage of upwards of 8GB on Linux. I
wonder if this is the same on Windows too?

David Truby

On Tue, 2020-07-28 at 17:03 -0500, Michael Kruse via flang-dev wrote:
> At yesterday's flang technical call, we wanted to have an additional
> data point for the build time of flang itself, by also getting the
> compilation time using msvc.
> Methodology:
> Using my personal notebook with Intel Core i7-7700HQ CPU @ 2.80GHz,
> 16GB RAM, Windows 10 1909. I could not find a reliable way to get the
> user/system time for a process tree under Windows, so I am using wall
> clock time and single threads (ninja -j1). To keep the build time
> reasonable, I only timed compilation flang itself and its f18
> executable (ninja says 130 tasks after touching every file in the
> flang subdirectory, consistent with every compiler).
> -DCMAKE_BUILD_TYPE=Release. I was using the computer while taking the
> time. Peak resident/working set size was determined using python
> psutil.
> Msvc has parallelized its code generation and uses 4 threads by
> default. To make numbers more comparable, I have another run where I
> switched this off (/cgthreads1).
> Results:
> GCC 7.5 (Ubuntu 18.04.4, WSL)
> Wall clock duration: 0:45:47
> Peak compiler resident size: 4042.9 MiB (by cc1plus PFTBuilder.cpp)
> Peak linker resident size: 151.8 MiB (by ld.lld f18)
> Clang 11.0.0 (release build 3e94943d, WSL)
> Wall clock duration: 1:42:22
> Peak compiler resident size: 3266.0 MiB (by clang++ PFTBuilder.cpp)  
> Peak linker resident size: 260.7 MiB (by ld.lld f18)  
> MSVC 19.26.28806 (Visual Studio 2019 16.6.5 -- current latest)
> Wall clock duration: 0:59:26
> Peak compiler working set: 7915.9 MiB (by cl.exe f18.cpp)
> Peak linker working set: 747.9 MiB (by link.exe f18.exe)
> MSVC /cgthreads1
> Wall clock duration: 1:32:19
> Peak compiler working set: 7918.3 MiB (by cl.exe f18.cpp)
> Peak linker working set: 747.9 MiB (by link.exe f18.exe)
> I also tried Intel icc, which unfortunately failed: tablegen does
> recognize its command line argument. I assume the cl::opt command
> line registration static initializer does not work.
> Michael
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