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Rewrite the PBQP graph data structure.

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The new graph structure replaces the node and edge linked lists with vectors.
Free lists (well, free vectors) are used for fast insertion/deletion.

The ultimate aim is to make PBQP graphs cheap to clone. The motivation is that
the PBQP solver destructively consumes input graphs while computing a solution,
forcing the graph to be fully reconstructed for each round of PBQP. This
imposes a high cost on large functions, which often require several rounds of
solving/spilling to find a final register allocation. If we can cheaply clone
the PBQP graph and incrementally update it between rounds then hopefully we can
reduce this cost. Further, once we begin pooling matrix/vector values (future
work), we can cache some PBQP solver metadata and share it between cloned
graphs, allowing the PBQP solver to re-use some of the computation done in
earlier rounds.

For now this is just a data structure update. The allocator and solver still
use the graph the same way as before, fully reconstructing it between each
round. I expect no material change from this update, although it may change
the iteration order of the nodes, causing ties in the solver to break in
different directions, and this could perturb the generated allocations
(hopefully in a completely benign way).

Thanks very much to Arnaud Allard de Grandmaison for encouraging me to get back
to work on this, and for a lot of discussion and many useful PBQP test cases.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194300 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Lang Hames
2013-11-09 00:14:07 +00:00
parent 623d2e618f
commit fc93ae629e
7 changed files with 446 additions and 416 deletions
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11
include/llvm/CodeGen/PBQP/Solution.h
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@ -26,8 +26,7 @@ namespace PBQP {
class Solution {
private:
typedef std::map<Graph::ConstNodeItr, unsigned,
NodeItrComparator> SelectionsMap;
typedef std::map<Graph::NodeId, unsigned> SelectionsMap;
SelectionsMap selections;
unsigned r0Reductions, r1Reductions, r2Reductions, rNReductions;
@ -73,15 +72,15 @@ namespace PBQP {
/// \brief Set the selection for a given node.
/// @param nItr Node iterator.
/// @param selection Selection for nItr.
void setSelection(Graph::NodeItr nItr, unsigned selection) {
selections[nItr] = selection;
void setSelection(Graph::NodeId nodeId, unsigned selection) {
selections[nodeId] = selection;
}
/// \brief Get a node's selection.
/// @param nItr Node iterator.
/// @return The selection for nItr;
unsigned getSelection(Graph::ConstNodeItr nItr) const {
SelectionsMap::const_iterator sItr = selections.find(nItr);
unsigned getSelection(Graph::NodeId nodeId) const {
SelectionsMap::const_iterator sItr = selections.find(nodeId);
assert(sItr != selections.end() && "No selection for node.");
return sItr->second;
}