On 03/07/2013 12:35 AM, Redmond, Paul wrote:
On 2013-03-06, at 3:42 PM, Pekka Jääskeläinen wrote:
Hi Paul,
On 03/06/2013 10:11 PM, Redmond, Paul wrote:
I have updated the patch to not add metadata on loads and stores where the
pointer comes from an alloca. I wonder if the check should be more
conservative and only include pointers coming from Arguments and GlobalValues
(perhaps Constants too?)
I think it's safer that way around for now.
Hmm.. I'm not sure that this approach (or my original) is general enough.
Here's a simple loop and the corresponding IR as generated by clang:
Before taking decisions on what exactly we need to do during code
generation, I would appreciate if we could write down the exact
semantics of #pragma ivdep on the C level. We should get a list of
interesting test cases and investigate what other compilers gcc and icc
do in such cases. Pekka and me gave a couple of test cases, that may be
a good start.
Regarding your current approach. I wonder if, instead of analyzing the
IR that clang generates, we could take decisions according to how
a certain memory access is/was represented at the C level. This is the
level the #pragma ivdep semantics are defined and this should allow us
to take the right conclusions.
A safe start would e.g. be to only annotate loads/stores that come from
array style memory accesses ala 'A[i][j]', where A was declared outside
of the loop that was marked with #pragma ivdep.
Cheers,
Tobi
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