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I don't think that arbitrary limiting the complexity of the search
is the right approach. There are numerous ways the LVI
infrastructure could be made more memory efficient. Fixing the
existing code to be memory efficient is the right approach. Only
once there's no more low hanging fruit should we even consider
clamping the search. <br>
<br>
In general, introducing clamps should be an absolute last resort.
We really don't want an optimizer than if fragile with respect to
code size and shape. <br>
<br>
Philip<br>
<br>
<div class="moz-cite-prefix">On 01/13/2016 02:27 PM, Joerg
Sonnenberger via llvm-dev wrote:<br>
</div>
<blockquote cite="mid:20160113222708.GA31592@britannica.bec.de"
type="cite">
<pre wrap="">Hi all,
with the current trunk I have two major cases where clang needs more
than 2GB memory for compiling programs with -O2. One is related to GVN
and MemoryDependenceAnalysis and has a pending patch. The other is
related to the Correlated Value Propagation and Lazy Value Information
cache. Attached is a heap profile for one of the relevant test cases.
Looking at the sources, I don't see any form of CFG limiters in LVI or
CVP, so it doesn't seem surprising that large memory use can be easily
triggered. This normally also corresponds to very slow compilation, so
it addressing it fixes two issues at the same time. A test case can be
found in <a class="moz-txt-link-freetext" href="https://llvm.org/bugs/show_bug.cgi?id=10584">https://llvm.org/bugs/show_bug.cgi?id=10584</a>.
The question for me is: where should such complexity limits be placed --
in the CVP pass or inside LVI? Is anyone specifically interested in
hunting down the problem?
Joerg
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