Current findBestLoopTop can find and move one kind of block to top, a latch block has one successor. Another common case is:
* a latch block
* it has two successors, one is loop header, another is exit
* it has more than one predecessors
If it is below one of its predecessors P, only P can fall through to it, all other predecessors need a jump to it, and another conditional jump to loop header. If it is moved before loop header, all its predecessors jump to it, then fall through to loop header. So all its predecessors except P can reduce one taken branch.
Differential Revision: https://reviews.llvm.org/D43256
llvm-svn: 363471
For the situation, where we generate the following code:
crxor 8, 8, 8
< Some instructions>
.LBB0_1:
< Some instructions>
cror 1, 8, 8
cror (COPY of CRbit) depends on the result of the crxor instruction.
CR8 is known to be zero as crxor is equivalent to CRUNSET. We can simply use
crxor 1, 1, 1 instead to zero out CR1, which does not have any dependency on
any previous instruction.
This patch will optimize it to:
< Some instructions>
.LBB0_1:
< Some instructions>
cror 1, 1, 1
Patch By: Victor Huang (NeHuang)
Differential Revision: https://reviews.llvm.org/D62044
llvm-svn: 361632
For known CRBit spills, CRSET/CRUNSET, it is more efficient to load and spill
the known value instead of extracting the bit.
eg. This sequence is currently used to spill a CRUNSET:
crclr 4*cr5+lt
mfocrf r3,4
rlwinm r3,r3,20,0,0
stw r3,132(r1)
This patch custom lower it to:
li r3,0
stw r3,132(r1)
Differential Revision: https://reviews.llvm.org/D61754
llvm-svn: 360677
Guozhi Wei