[llvm-mca] Teach how to identify serializing instructions. #36016
Description
| Bugzilla Link | 36668 |
| Version | trunk |
| OS | All |
| CC | @legrosbuffle,@RKSimon,@rotateright |
Extended Description
Similar to bug 36667.
However, serializing operations block the Backend until all the are no other instructions in-flight. Essentially, these instructions block the Dispatch, and force all the in-flight instructions to complete before new instructions are dispatched.
This could be fixed by using an extra flag in MCInstrDesc.
In llvm-mca, this requires a few changes in the Backend/DispatchUnit logic. At the moment, the tool doesn't know about serializing instructions.
Examples of non-privileged serializing instructions on X86 are:
CPUID, IRET