ira.c: Add comment about threads at the top of file.
2013-11-13 Vladimir Makarov <vmakarov@redhat.com> * ira.c: Add comment about threads at the top of file. From-SVN: r204772
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@ -1,3 +1,7 @@
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2013-11-13 Vladimir Makarov <vmakarov@redhat.com>
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* ira.c: Add comment about threads at the top of file.
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2013-11-13 Vladimir Makarov <vmakarov@redhat.com>
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* ira-color.c (coalesce_allocnos): Don't allocate and free
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@ -192,7 +192,14 @@ along with GCC; see the file COPYING3. If not see
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this point. There is some freedom in the order of putting
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allocnos on the stack which can affect the final result of
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the allocation. IRA uses some heuristics to improve the
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order.
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order. The major one is to form *threads* from colorable
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allocnos and push them on the stack by threads. Thread is a
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set of non-conflicting colorable allocnos connected by
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copies. The thread contains allocnos from the colorable
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bucket or colorable allocnos already pushed onto the coloring
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stack. Pushing thread allocnos one after another onto the
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stack increases chances of removing copies when the allocnos
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get the same hard reg.
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We also use a modification of Chaitin-Briggs algorithm which
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works for intersected register classes of allocnos. To
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