diff options
Diffstat (limited to 'src/cmd/compile/internal/ssa/prove.go')
| -rw-r--r-- | src/cmd/compile/internal/ssa/prove.go | 32 |
1 files changed, 26 insertions, 6 deletions
diff --git a/src/cmd/compile/internal/ssa/prove.go b/src/cmd/compile/internal/ssa/prove.go index 233d0b30d1..3de964f061 100644 --- a/src/cmd/compile/internal/ssa/prove.go +++ b/src/cmd/compile/internal/ssa/prove.go @@ -436,6 +436,29 @@ func (l limit) bitlen(b uint) limit { ) } +// Similar to add, but computes the PopCount of the limit for bitsize b. +func (l limit) popcount(b uint) limit { + fixed, fixedCount := l.unsignedFixedLeadingBits() + varying := 64 - fixedCount + fixedContribution := uint64(bits.OnesCount64(fixed)) + + min := fixedContribution + max := fixedContribution + uint64(varying) + + varyingMask := uint64(1)<<varying - 1 + + if varyingPartOfUmax := l.umax & varyingMask; uint(bits.OnesCount64(varyingPartOfUmax)) != varying { + // there is at least one zero bit in the varying part + max-- + } + if varyingPartOfUmin := l.umin & varyingMask; varyingPartOfUmin != 0 { + // there is at least one non-zero bit in the varying part + min++ + } + + return noLimit.unsignedMinMax(min, max) +} + var noLimit = limit{math.MinInt64, math.MaxInt64, 0, math.MaxUint64} // a limitFact is a limit known for a particular value. @@ -1942,12 +1965,9 @@ func (ft *factsTable) flowLimit(v *Value) { ft.newLimit(v, al.ctz(uint(a.Type.Size())*8)) case OpPopCount64, OpPopCount32, OpPopCount16, OpPopCount8: - a := ft.limits[v.Args[0].ID] - changingBitsCount := uint64(bits.Len64(a.umax ^ a.umin)) - sharedLeadingMask := ^(uint64(1)<<changingBitsCount - 1) - fixedBits := a.umax & sharedLeadingMask - min := uint64(bits.OnesCount64(fixedBits)) - ft.unsignedMinMax(v, min, min+changingBitsCount) + a := v.Args[0] + al := ft.limits[a.ID] + ft.newLimit(v, al.popcount(uint(a.Type.Size())*8)) case OpBitLen64, OpBitLen32, OpBitLen16, OpBitLen8: a := v.Args[0] |