Skip to content

SystemTools: Implement GetEnv via GetEnvironmentVariableW on Win32

Clemens Wasser requested to merge clemenswasser/kwsys:Win32GetEnvironmentVariableW into master

The GetEnvironmentVariableW function from the Win32 API is way faster than the previously used _wgetenv C-stdlib function. Using this patch, CMake can configure the llvm-project codebase ~7% faster on Windows:

> hyperfine -w 1 -S 'pwsh' 'rm -r -fo build-perf; D:\dev\cpp\cmake\master\build-msvc-release\bin\cmake.exe -G Ninja -B build-perf -D CMAKE_BUILD_TYPE=Debug llvm' -n master 'rm -r -fo build-perf; D:\dev\cpp\cmake\Win32GetEnvironmentVariableW\build-msvc-release\bin\cmake.exe -G Ninja -B build-perf -D CMAKE_BUILD_TYPE=Debug llvm' -n Win32GetEnvironmentVariableW
Benchmark 1: master
  Time (mean ± σ):     21.105 s ±  0.134 s    [User: 0.052 s, System: 0.134 s]
  Range (min … max):   20.955 s … 21.411 s    10 runs

Benchmark 2: Win32GetEnvironmentVariableW
  Time (mean ± σ):     19.816 s ±  0.124 s    [User: 0.049 s, System: 0.172 s]
  Range (min … max):   19.646 s … 20.041 s    10 runs

Summary
  Win32GetEnvironmentVariableW ran
    1.07 ± 0.01 times faster than master

Merge request reports