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[SystemZ] Update README 

llvm-svn: 188062
This commit is contained in:
Richard Sandiford 2013-08-09 09:25:57 +00:00
parent 89085340be
commit 9140910be8
1 changed files with 5 additions and 15 deletions
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20
llvm/lib/Target/SystemZ/README.txt
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@ -47,7 +47,7 @@ There is no scheduling support.
--
We don't use the BRANCH ON COUNT or BRANCH ON INDEX families of instruction.
We don't use the BRANCH ON INDEX instructions.
--
@ -56,18 +56,7 @@ and conditional returns.
--
We don't use the condition code results of anything except comparisons.
Implementing this may need something more finely grained than the z_cmp
and z_ucmp that we have now. It might (or might not) also be useful to
have a mask of "don't care" values in conditional branches. For example,
integer comparisons never set CC to 3, so the bottom bit of the CC mask
isn't particularly relevant. JNLH and JE are equally good for testing
equality after an integer comparison, etc.
--
We don't use the LOAD AND TEST or TEST DATA CLASS instructions.
We don't use the TEST DATA CLASS instructions.
--
@ -77,9 +66,10 @@ condition codes. For example, we could use LCDFR instead of LCDBR.
--
We don't optimize block memory operations.
We don't optimize block memory operations, except using single MVCs
for memcpy.
It's definitely worth using things like MVC, CLC, NC, XC and OC with
It's definitely worth using things like CLC, NC, XC and OC with
constant lengths. MVCIN may be worthwhile too.
We should probably implement things like memcpy using MVC with EXECUTE.