UniformityInfo has a transitive dependence on CycleInfo. A transform may
change the CFG in trivial ways that do not affect uniformity, but that
can leave cycles in a slightly inconsistent state. In the absence of
updates to CycleInfo, it's cleaner to just invalidate both analyses.
This patch ports the AMDGPURewriteUndefForPHI pass to the new pass
manager. With this, the pass is supported under both the legacy and the
new pass managers.
---------
Co-authored-by: Jun Wang <jun.wang7@amd.com>
For the pattern of IR (%if terminates with a divergent branch.),
divergence analysis will report %phi as uniform to help optimal code
generation.
```
%if
| \
| %then
| /
%endif: %phi = phi [ %uniform, %if ], [ %undef, %then ]
```
In the backend, %phi and %uniform will be assigned a scalar register.
But the %undef from %then will make the scalar register dead in %then.
This will likely cause the register being over-written in %then. To fix
the issue, we will rewrite %undef as %uniform. For details, please refer
the comment in AMDGPURewriteUndefForPHI.cpp. Currently there is no test
changes shown, but this is mandatory for later changes.
Reviewed by: sameerds
Differential Revision: https://reviews.llvm.org/D133840
