vitalybuka added a reviewer: vitalybuka.
vitalybuka added a comment.

In D134410#3817190 <https://reviews.llvm.org/D134410#3817190>, @vitalybuka 
wrote:

>> Also I applied this patch with D134698 <https://reviews.llvm.org/D134698> 
>> and used on our large test set, expecting significant number of pre-existing 
>> reports. To my surprise I see not many of them.
>
> Something wrong with my msan experiment, I'll re-evaluate size and reports 
> tomorrow.

Finally I had a time to fix my msan experiment D134698 
<https://reviews.llvm.org/D134698>
It's about 5.5% .text savings for Msan, and 10% for msan with "track origins", 
which is pretty good.
For context, for msan it's usually cheaper to report uninitialized ASAP, then 
propagating and report it later. With this metadata it will happen immediately 
after load.

However cleanup looks scary. Msan reports maybe 20% of unique tests on our code 
base. Many a of them share root cause, but still many unique root causes.
On quick looks I see no false report. A lot of stuff like this 
https://stackoverflow.com/questions/60112841/copying-structs-with-uninitialized-members
 which is technically is UB.
I assume with this patch landed, many such cases may change code behavior. So 
we will need to update msan to have a tool to detect cases like this anyway.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D134410/new/

https://reviews.llvm.org/D134410

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