[PATCH] D106206: Lazy initialized the NotUnderValgrind flag

Mon Jul 19 16:52:16 PDT 2021

mehdi_amini added inline comments.

================
Comment at: llvm/lib/Support/Valgrind.cpp:27-38
+namespace {
+struct CreateNotUnderValgrind {
+  static void *call() { return new bool{!RUNNING_ON_VALGRIND}; }
+};
+} // namespace
+static const llvm::ManagedStatic<bool, CreateNotUnderValgrind> NotUnderValgrind;

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dexonsmith wrote:
> mehdi_amini wrote:
> > dexonsmith wrote:
> > > dexonsmith wrote:
> > > > Can `NotUnderValgrind` be merged into `RunningOnValgrind`, skipping the managed static?
> > > > 
> > > > The only reason not to is if it `RUNNING_ON_VALGRIND` could return "true" on the first use, but "false" some time later in the same execution. I don't imagine that's possible...?
> > > > 
> > > > ... but if it //is// possible, maybe switching to ManagedStatic isn't safe either, since there would be a reason to cache the value at load-time instead of at first use.
> > > (Based on https://www.valgrind.org/docs/manual/manual-core-adv.html I strongly doubt load-time is special in any way...)
> > Yeah I'm confused by all this logic, and I didn't get the comment either. I don't get why we don't just `return RUNNING_ON_VALGRIND` and forget about caching entirely?
> Maybe there was a time when it wasn't fast? Might be worth a quick look at git-blame to see if this was in response to a specific performance problem. Might be better to remove the caching entirely.
No I had looked and it was added as part of the original revision: https://github.com/llvm/llvm-project/commit/3ddd88f523defacb922ea53e64fec2bdf25f2896#diff-d5d0a3cfb6f89c8c0d2367f426b48e438acce79ff3ddaff17c3ed1ada2ae5693

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D106206/new/

https://reviews.llvm.org/D106206