I noticed that unit_tests.exe runs really slowly when I enabled 64-bit ASan. Profiling shows that all the time is spent in CreateProcess -> MiCopyToCfgBitMap. My best theory explaining this slowdown is that ASan binaries are almost five times the size of non-asan test binaries, and the CFG bitmap is probably proportional to the size of the images loaded in the child process.

We should try to reduce the ASan code size overhead if possible. I have a few ideas. I want to re-enable C string merging. That should save a fair amount of readonly data, but not code.

I also noticed that we load the global shadow address even if a function contains no memory accesses. That seems like an easy small code size win.

We should consider a higher overhead call instrumentation mode. This has been requested in the past because it would allow disabling ASan instrumentation at runtime, perhaps during process startup, after a crash has been reported.