This hashing scheme has been useful out of tree, and I want to start
experimenting with it. Specifically I want to experiment on the
MIRVRegNamer, MIRCanononicalizer, and eventually the MachineOutliner.
This diff is a first step, that optionally brings stable hashing to the
MIRVRegNamer (and as a result, the MIRCanonicalizer). We've tested this
hashing scheme on a lot of MachineOperand types that llvm::hash_value
can not handle in a stable manner.
This stable hashing was also the basis for
"Global Machine Outliner for ThinLTO" in EuroLLVM 2020
http://llvm.org/devmtg/2020-04/talks.html#TechTalk_58
Credits: Kyungwoo Lee, Nikolai Tillmann
Differential Revision: https://reviews.llvm.org/D86952
This patch makes it so that cases where multiple instructions that
differ only in their ConstantInt or ConstantFP MachineOperand values no
longer collide. For instance:
%0:_(s1) = G_CONSTANT i1 true
%1:_(s1) = G_CONSTANT i1 false
%2:_(s32) = G_FCONSTANT float 1.0
%3:_(s32) = G_FCONSTANT float 0.0
Prior to this patch the first two instructions would collide together.
Also, the last two G_FCONSTANT instructions would also collide. Now they
will no longer collide.
Differential Revision: https://reviews.llvm.org/D71558
Puyan Lotfi