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author | Duncan P. N. Exon Smith <dexonsmith@apple.com> | 2014-04-29 16:15:35 +0000 |
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committer | Duncan P. N. Exon Smith <dexonsmith@apple.com> | 2014-04-29 16:15:35 +0000 |
commit | 048f520b91e5fcabb1aa85cae3ec522ab5a539e6 (patch) | |
tree | e263b166b42d4f06416f0553649ec9eb871a4bb8 /lib/Support/BranchProbability.cpp | |
parent | f90262a09d35f9aba24357196f961733a4291aba (diff) | |
download | llvm-048f520b91e5fcabb1aa85cae3ec522ab5a539e6.tar.gz llvm-048f520b91e5fcabb1aa85cae3ec522ab5a539e6.tar.bz2 llvm-048f520b91e5fcabb1aa85cae3ec522ab5a539e6.tar.xz |
Support: Add BranchProbability::scale() and ::scaleByInverse()
Add API to `BranchProbability` for scaling big integers. Next job is to
rip the logic out of `BlockMass` and `BlockFrequency`.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207544 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'lib/Support/BranchProbability.cpp')
-rw-r--r-- | lib/Support/BranchProbability.cpp | 47 |
1 files changed, 47 insertions, 0 deletions
diff --git a/lib/Support/BranchProbability.cpp b/lib/Support/BranchProbability.cpp index e8b83e5980..c541fca3fb 100644 --- a/lib/Support/BranchProbability.cpp +++ b/lib/Support/BranchProbability.cpp @@ -26,6 +26,53 @@ void BranchProbability::dump() const { dbgs() << *this << '\n'; } +static uint64_t scale(uint64_t Num, uint32_t N, uint32_t D) { + assert(D && "divide by 0"); + + // Fast path for multiplying by 1.0. + if (!Num || D == N) + return Num; + + // Split Num into upper and lower parts to multiply, then recombine. + uint64_t ProductHigh = (Num >> 32) * N; + uint64_t ProductLow = (Num & UINT32_MAX) * N; + + // Split into 32-bit digits. + uint32_t Upper32 = ProductHigh >> 32; + uint32_t Lower32 = ProductLow & UINT32_MAX; + uint32_t Mid32Partial = ProductHigh & UINT32_MAX; + uint32_t Mid32 = Mid32Partial + (ProductLow >> 32); + + // Carry. + Upper32 += Mid32 < Mid32Partial; + + // Check for overflow. + if (Upper32 >= D) + return UINT64_MAX; + + uint64_t Rem = (uint64_t(Upper32) << 32) | Mid32; + uint64_t UpperQ = Rem / D; + + // Check for overflow. + if (UpperQ > UINT32_MAX) + return UINT64_MAX; + + Rem = ((Rem % D) << 32) | Lower32; + uint64_t LowerQ = Rem / D; + uint64_t Q = (UpperQ << 32) + LowerQ; + + // Check for overflow. + return Q < LowerQ ? UINT64_MAX : Q; +} + +uint64_t BranchProbability::scale(uint64_t Num) const { + return ::scale(Num, N, D); +} + +uint64_t BranchProbability::scaleByInverse(uint64_t Num) const { + return ::scale(Num, D, N); +} + namespace llvm { raw_ostream &operator<<(raw_ostream &OS, const BranchProbability &Prob) { |