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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@26585 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2006-03-07 04:42:59 +00:00
parent 784236d778
commit 5a63c47fb5
1 changed files with 14 additions and 0 deletions
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14
lib/Target/PowerPC/README.txt
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@ -452,3 +452,17 @@ _test:
srwi r3, r2, 24
blr
===-------------------------------------------------------------------------===
On the G5, logical CR operations are more expensive in their three
address form: ops that read/write the same register are half as expensive as
those that read from two registers that are different from their destination.
We should model this with two separate instructions. The isel should generate
the "two address" form of the instructions. When the register allocator
detects that it needs to insert a copy due to the two-addresness of the CR
logical op, it will invoke PPCInstrInfo::convertToThreeAddress. At this point
we can convert to the "three address" instruction, to save code space.
This only matters when we start generating cr logical ops.