6502/llvm-6502
1
0
Fork 0
mirror of https://github.com/c64scene-ar/llvm-6502.git synced 2025-07-15 19:24:33 +00:00
Code Issues Projects Releases Wiki Activity

blockfreq: Defer to BranchProbability::scale()

Browse Source 
`BlockMass` can now defer to `BranchProbability::scale()`.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207547 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Duncan P. N. Exon Smith
2014-04-29 16:20:05 +00:00
parent 81566c52fd
commit 6919443535
2 changed files with 4 additions and 51 deletions
Download Patch File Download Diff File Expand all files Collapse all files

29
include/llvm/Analysis/BlockFrequencyInfoImpl.h
View File

@@ -758,31 +758,10 @@ public:
return *this;
}
/// \brief Multiply by a branch probability.
///
/// Multiply by P. Guarantees full precision.
///
/// This could be naively implemented by multiplying by the numerator and
/// dividing by the denominator, but in what order? Multiplying first can
/// overflow, while dividing first will lose precision (potentially, changing
/// a non-zero mass to zero).
///
/// The implementation mixes the two methods. Since \a BranchProbability
/// uses 32-bits and \a BlockMass 64-bits, shift the mass as far to the left
/// as there is room, then divide by the denominator to get a quotient.
/// Multiplying by the numerator and right shifting gives a first
/// approximation.
///
/// Calculate the error in this first approximation by calculating the
/// opposite mass (multiply by the opposite numerator and shift) and
/// subtracting both from teh original mass.
///
/// Add to the first approximation the correct fraction of this error value.
/// This time, multiply first and then divide, since there is no danger of
/// overflow.
///
/// \pre P represents a fraction between 0.0 and 1.0.
BlockMass &operator*=(const BranchProbability &P);
BlockMass &operator*=(const BranchProbability &P) {
Mass = P.scale(Mass);
return *this;
}
bool operator==(const BlockMass &X) const { return Mass == X.Mass; }
bool operator!=(const BlockMass &X) const { return Mass != X.Mass; }