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Add an interface to scale the frequencies of a set of blocks.

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The scaling is done with reference to the the new frequency of a reference block.

Differential Revision: https://reviews.llvm.org/D28535

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@292507 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Easwaran Raman 2017-01-19 18:53:16 +00:00
parent 02d80d355e
commit d91b01bb76
3 changed files with 36 additions and 0 deletions
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6
include/llvm/Analysis/BlockFrequencyInfo.h
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@ -73,6 +73,12 @@ public:
// Set the frequency of the given basic block.
void setBlockFreq(const BasicBlock *BB, uint64_t Freq);
/// Set the frequency of \p ReferenceBB to \p Freq and scale the frequencies
/// of the blocks in \p BlocksToScale such that their frequencies relative
/// to \p ReferenceBB remain unchanged.
void setBlockFreqAndScale(const BasicBlock *ReferenceBB, uint64_t Freq,
SmallPtrSetImpl<BasicBlock *> &BlocksToScale);
/// calculate - compute block frequency info for the given function.
void calculate(const Function &F, const BranchProbabilityInfo &BPI,
const LoopInfo &LI);

22
lib/Analysis/BlockFrequencyInfo.cpp
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@ -180,6 +180,28 @@ void BlockFrequencyInfo::setBlockFreq(const BasicBlock *BB, uint64_t Freq) {
BFI->setBlockFreq(BB, Freq);
}
void BlockFrequencyInfo::setBlockFreqAndScale(
const BasicBlock *ReferenceBB, uint64_t Freq,
SmallPtrSetImpl<BasicBlock *> &BlocksToScale) {
assert(BFI && "Expected analysis to be available");
// Use 128 bits APInt to avoid overflow.
APInt NewFreq(128, Freq);
APInt OldFreq(128, BFI->getBlockFreq(ReferenceBB).getFrequency());
APInt BBFreq(128, 0);
for (auto *BB : BlocksToScale) {
BBFreq = BFI->getBlockFreq(BB).getFrequency();
// Multiply first by NewFreq and then divide by OldFreq
// to minimize loss of precision.
BBFreq *= NewFreq;
// udiv is an expensive operation in the general case. If this ends up being
// a hot spot, one of the options proposed in
// https://reviews.llvm.org/D28535#650071 could be used to avoid this.
BBFreq = BBFreq.udiv(OldFreq);
BFI->setBlockFreq(BB, BBFreq.getLimitedValue());
}
BFI->setBlockFreq(ReferenceBB, Freq);
}
/// Pop up a ghostview window with the current block frequency propagation
/// rendered using dot.
void BlockFrequencyInfo::view() const {

8
unittests/Analysis/BlockFrequencyInfoTest.cpp
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@ -80,6 +80,14 @@ TEST_F(BlockFrequencyInfoTest, Basic) {
EXPECT_EQ(BFI.getBlockProfileCount(BB3).getValue(), UINT64_C(100));
EXPECT_EQ(BFI.getBlockProfileCount(BB1).getValue(), 100 * BB1Freq / BB0Freq);
EXPECT_EQ(BFI.getBlockProfileCount(BB2).getValue(), 100 * BB2Freq / BB0Freq);
// Scale the frequencies of BB0, BB1 and BB2 by a factor of two.
SmallPtrSet<BasicBlock *, 4> BlocksToScale({BB1, BB2});
BFI.setBlockFreqAndScale(&BB0, BB0Freq * 2, BlocksToScale);
EXPECT_EQ(BFI.getBlockFreq(&BB0).getFrequency(), 2 * BB0Freq);
EXPECT_EQ(BFI.getBlockFreq(BB1).getFrequency(), 2 * BB1Freq);
EXPECT_EQ(BFI.getBlockFreq(BB2).getFrequency(), 2 * BB2Freq);
EXPECT_EQ(BFI.getBlockFreq(BB3).getFrequency(), BB3Freq);
}
} // end anonymous namespace