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From "Evgueni Brevnov (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HARMONY-4620) [drlvm][jit] Long return path for floating point values in calling convention
Date Wed, 05 Mar 2008 13:47:41 GMT

    [ https://issues.apache.org/jira/browse/HARMONY-4620?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12575342#action_12575342

Evgueni Brevnov commented on HARMONY-4620:

As far as I remember we agreed to support processors which has SSE at least. I believe no
one tried Harmony on non-SSE processors. I don't think we should care about this case. 


> [drlvm][jit] Long return path for floating point values in calling convention
> -----------------------------------------------------------------------------
>                 Key: HARMONY-4620
>                 URL: https://issues.apache.org/jira/browse/HARMONY-4620
>             Project: Harmony
>          Issue Type: Improvement
>          Components: DRLVM
>         Environment: appropriate for for Intel architecture
>            Reporter: Naumova Natalya 
>            Assignee: Mikhail Fursov
>         Attachments: return_xmm.patch, return_xmm_2.patch, return_xmm_3.patch
> DRLVM has too long return path when the return value is floatin point. The reason is
FPU usage together with SSE instructions in calling convention: we have "SSE -> mem ->
FPU -> (return) mem -> SSE"; return (double) value first is calculated on xmm* registers,
then copied to mem, then is put on FPU stack, then extracted from this stack (in calling proc)
to memory again, then again calculation is happened in xmm* registers (SSE instructions).
This issue overrides the improvement with loop unrolling, overhead from the parameters passing
with this calling convention overrides the loop body doubling speed-up. When you increase
"arg.optimizer.unroll.medium_loop_unroll_count" option in method where return value is double
and it is in loop, then you'll have degradation (example - MonteCarlo benchmark in SciMark).
> Can we avoid using FPU with SSE in this case?

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