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Support: Add BranchProbability::scale() and ::scaleByInverse()

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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
This commit is contained in:
Duncan P. N. Exon Smith
2014-04-29 16:15:35 +00:00
parent f90262a09d
commit 048f520b91
3 changed files with 139 additions and 0 deletions
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47
lib/Support/BranchProbability.cpp
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@ -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) {