Details: https://reviews.llvm.org/D96805 changed the GCNTTIImpl::getCFInstrCost to return 1 for the PHI nodes
for the TTI::TCK_CodeSize and TTI::TCK_SizeAndLatency. This is incorrect because the value moves that are the
result of the PHI lowering are inserted into the basic block predecessors - not into the block itself.
As a result of this change LoopRotate and LoopUnroll were broken because of the incorrect Loop header and loop
body size/cost estimation.
Reviewed By: rampitec
Differential Revision: https://reviews.llvm.org/D105104
Added cost estimation for switch instruction, updated costs of branches, fixed
phi cost.
Had to increase `-amdgpu-unroll-threshold-if` default value since conditional
branch cost (size) was corrected to higher value.
Test renamed to "control-flow.ll".
Removed redundant code in `X86TTIImpl::getCFInstrCost()` and
`PPCTTIImpl::getCFInstrCost()`.
Reviewed By: rampitec
Differential Revision: https://reviews.llvm.org/D96805
Daniil Fukalov