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52610d84ad
llvm/lib/Transforms/IPO
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Karthik Bhat 52610d84ad Add a new pass "Loop Interchange" 
This pass interchanges loops to provide a more cache-friendly memory access.

For e.g. given a loop like -
  for(int i=0;i<N;i++)
    for(int j=0;j<N;j++)
      A[j][i] = A[j][i]+B[j][i];

is interchanged to -
  for(int j=0;j<N;j++)
    for(int i=0;i<N;i++)
      A[j][i] = A[j][i]+B[j][i];

This pass is currently disabled by default.

To give a brief introduction it consists of 3 stages-

LoopInterchangeLegality : Checks the legality of loop interchange based on Dependency matrix.
LoopInterchangeProfitability: A very basic heuristic has been added to check for profitibility. This will evolve over time.
LoopInterchangeTransform : Which does the actual transform.

LNT Performance tests shows improvement in Polybench/linear-algebra/kernels/mvt and Polybench/linear-algebra/kernels/gemver becnmarks.

TODO:
1) Add support for reductions and lcssa phi.
2) Improve profitability model.
3) Improve loop selection algorithm to select best loop for interchange. Currently the innermost loop is selected for interchange.
4) Improve compile time regression found in llvm lnt due to this pass.
5) Fix issues in Dependency Analysis module.

A special thanks to Hal for reviewing this code.
Review: http://reviews.llvm.org/D7499




git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@231458 91177308-0d34-0410-b5e6-96231b3b80d8
2015-03-06 10:11:25 +00:00
..
ArgumentPromotion.cpp Make DataLayout Non-Optional in the Module 2015-03-04 18:43:29 +00:00
BarrierNoopPass.cpp
CMakeLists.txt Introduce bitset metadata format and bitset lowering pass. 2015-02-20 20:30:47 +00:00
ConstantMerge.cpp Make DataLayout Non-Optional in the Module 2015-03-04 18:43:29 +00:00
DeadArgumentElimination.cpp DeadArgElim: aggregate Return assessment properly. 2015-02-11 23:13:11 +00:00
ExtractGV.cpp
FunctionAttrs.cpp [PM] Separate the TargetLibraryInfo object from the immutable pass. 2015-01-15 10:41:28 +00:00
GlobalDCE.cpp
GlobalOpt.cpp Make DataLayout Non-Optional in the Module 2015-03-04 18:43:29 +00:00
InlineAlways.cpp
Inliner.cpp Make DataLayout Non-Optional in the Module 2015-03-04 18:43:29 +00:00
InlineSimple.cpp
Internalize.cpp
IPConstantPropagation.cpp
IPO.cpp Introduce bitset metadata format and bitset lowering pass. 2015-02-20 20:30:47 +00:00
LLVMBuild.txt Update libdeps since TLI was moved from Target to Analysis in r226078. 2015-01-15 05:21:00 +00:00
LoopExtractor.cpp [PM] Lift the analyses into the interface for 2015-01-19 03:03:39 +00:00
LowerBitSets.cpp Make DataLayout Non-Optional in the Module 2015-03-04 18:43:29 +00:00
Makefile
MergeFunctions.cpp Make DataLayout Non-Optional in the Module 2015-03-04 18:43:29 +00:00
PartialInlining.cpp Add range adapters predecessors() and successors() for BBs 2015-02-04 19:14:57 +00:00
PassManagerBuilder.cpp Add a new pass "Loop Interchange" 2015-03-06 10:11:25 +00:00
PruneEH.cpp Don't promote asynch EH invokes of nounwind functions to calls 2015-02-11 01:23:16 +00:00
StripDeadPrototypes.cpp
StripSymbols.cpp