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[MachineCSE][MachinePRE] Avoid hoisting code from code regions into hot BBs.

Authored by lkail on Jul 19 2019, 5:58 AM.

Description

[MachineCSE][MachinePRE] Avoid hoisting code from code regions into hot BBs.

Summary:
Current PRE hoists common computations into
CMBB = DT->findNearestCommonDominator(MBB, MBB1).
However, if CMBB is in a hot loop body, we might get performance
degradation.

Differential Revision: https://reviews.llvm.org/D64394

llvm-svn: 366570

Event Timeline

Should be backported to 9.0 branch?

Hi @xbolva00 , I have some concern that @anton-afanasyev might have plan to revert some patches related to these files. If not so, I'll backport it to 9.0.