[llvm-commits] [PATCH 0/5] Reduce memory usage for phi operands

[Jay Foad]

Currently, a PHINode has 2 * n operands laid out like this:

  VAL0, BB0, VAL1, BB1, ..., VALn-1, BBn-1

Chris suggested to me that the BBn operands don't need to be full-blown Uses; they can just be pointers to the BasicBlock. This should be a win because:

- Uses are bulky and slow to access
- This keeps phi nodes off BasicBlocks' use lists, which should make it faster to enumerate a BasicBlock's predecessors.

The following patches implement this suggestion. PHINodes now have n operands, immediately followed in memory by n pointers to basic blocks, like this:

  VAL0, VAL1, ..., VALn-1; bb0, bb1, ..., bbn-1


I used "valgrind --tool=massif --peak-inaccuracy=0" to measure peak heap memory usage before and after my changes, for the following commands (using source from MultiSource/Applications/sqlite3/):

$ clang -cc1 -emit-llvm-bc -o /dev/null sqlite3.c -O3
before 87475624
after 87164488 (down by 0.36%)

$ llvm-ld sqlite3.o shell.o
before 40417072
after 40101936 (down by 0.78%)


Here is the elapsed run time in seconds for 5 runs of the following command:

$ clang -cc1 -emit-llvm-bc -o /dev/null sqlite3.c -O3
before 5.816 5.842 5.836 5.828 5.840
after 5.729 5.735 5.735 5.738 5.723 (down by 1.7% on average)


Tested with:

- make all check-all, LLVM and Clang
- nightly test suite with llvm-gcc-4.2
- nightly test suite with dragonegg
- nightly test suite with Clang

OK to commit?


Jay Foad (5):
  Remove the AugmentedUse struct.
  Make better use of the PHINode API.
  Change how PHINodes store their operands.
  Extend replaceAllUsesWith() on a BasicBlock.
  Test case.

 include/llvm/BasicBlock.h                     |    6 +-
 include/llvm/Instructions.h                   |   81 ++++++++++++-------
 include/llvm/Support/CFG.h                    |    2 +-
 include/llvm/Use.h                            |   19 ++---
 lib/Bitcode/Writer/BitcodeWriter.cpp          |   12 ++-
 lib/Target/CppBackend/CPPBackend.cpp          |    5 +-
 lib/Transforms/Scalar/GVN.cpp                 |   13 ++-
 lib/Transforms/Scalar/LoopRotation.cpp        |    2 +-
 lib/Transforms/Scalar/LoopUnswitch.cpp        |    8 +-
 lib/Transforms/Utils/BasicBlockUtils.cpp      |    6 +-
 lib/Transforms/Utils/BreakCriticalEdges.cpp   |   54 ++++---------
 lib/Transforms/Utils/CloneFunction.cpp        |    6 +-
 lib/Transforms/Utils/InlineFunction.cpp       |   10 +-
 lib/Transforms/Utils/Local.cpp                |   17 +++--
 lib/Transforms/Utils/LoopUnroll.cpp           |   71 +++++++++--------
 lib/Transforms/Utils/ValueMapper.cpp          |   14 +++
 lib/VMCore/AsmWriter.cpp                      |    8 +-
 lib/VMCore/BasicBlock.cpp                     |   20 ++++-
 lib/VMCore/Instructions.cpp                   |   54 +++++++------
 lib/VMCore/Use.cpp                            |    8 +-
 lib/VMCore/User.cpp                           |   12 +--
 lib/VMCore/Value.cpp                          |    3 +
 lib/VMCore/Verifier.cpp                       |   14 ++--
 test/Transforms/GVN/2011-04-27-phioperands.ll |  106 +++++++++++++++++++++++++
 24 files changed, 357 insertions(+), 194 deletions(-)
 create mode 100644 test/Transforms/GVN/2011-04-27-phioperands.ll

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1.7.4.1