This CL adds a new discriminator pass. Also adds a new sample profile
loading pass when MFS is enabled.
Differential Revision: https://reviews.llvm.org/D152577
This change enables loading pseudo-probe based profile on MIR. Different from the IR profile loader, callsites are excluded from MIR profile loading since they are not assinged a FS discriminator. Using zero as the discriminator is not accurate and would undo the distribution work done by the IR loader based on pseudo probe distribution factor. We reply on block probes only for FS profile loading.
Some refactoring is done to the IR profile loader so that `getProbeWeight` can be shared by both loaders.
Reviewed By: wenlei
Differential Revision: https://reviews.llvm.org/D148584
This change improves FS discriminators in the following ways:
(1) use call-stack debug information in the the to generate
discriminators: the same (src/line) DILs can now have same
discriminator value if they come from different call-stacks.
This effectively increases the usable discriminator values
for each round of FS discriminator pass.
(2) don't generate the FS discriminator for meta instructions
(i.e. instructions not emitted). This reduces the number
discriminators conflicts (for the case we run out of discriminator
bits for that pass).
(3) use less expensive hashing of xxHash64.
These improvements should bring better performance for FSAFDO
and they should be used by default. But this change creates
incompatible FS discriminators. For the iterative profile users,
they might see a performance drop in the first release with
this change (due to the fact that the profiles have the old
discriminators and the compiler uses the new discriminator).
We have measured that this is not more than 1.5% on several
benchmarks. Note the degradation should be gone in the second
release and one should expect a performance gain over the binary
without this change.
One possible solution to the iterative profile issue would be
separating discriminators for profile-use and the ones emitted to
the binary. This would require a mechanism to allow two sets of
discriminators to be maintained and then phasing out the first
approach. This is too much churn in the compiler and the
performance implications do not seem to be worth the effort.
Instead, we put the changes under an option so iterative profile
users can do a gradual rollout of this change. We will make the
option default value to true in a later patch and eventually
purge this option from the code base.
Differential Revision: https://reviews.llvm.org/D145171
This patch implements Flow Sensitive Sample FDO (FSAFDO) profile
loader. We have two profile loaders for FS profile,
one before RegAlloc and one before BlockPlacement.
To enable it, when -fprofile-sample-use=<profile> is specified,
add "-enable-fs-discriminator=true \
-disable-ra-fsprofile-loader=false \
-disable-layout-fsprofile-loader=false"
to turn on the FS profile loaders.
Differential Revision: https://reviews.llvm.org/D107878
