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cmd/compile: add limits bruteforce tests for bitlen

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This ensure BitLen is perfect within the limitations limits can represent.

Change-Id: I5c1770b4a9f6408fd68fe77b4ef2b2cdd52e26cb
Reviewed-on: https://go-review.googlesource.com/c/go/+/727781
Reviewed-by: Keith Randall <khr@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Jorropo <jorropo.pgm@gmail.com>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>
This commit is contained in:
Jorropo
2025-12-07 03:07:46 +01:00
committed by Gopher Robot
parent a4fda8d32a
commit 417d5e6627
2 changed files with 16 additions and 20 deletions
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32
src/cmd/compile/internal/ssa/prove.go
View File

@@ -428,6 +428,14 @@ func (l limit) ctz(b uint) limit {
return noLimit.unsignedMax(uint64(min(uint(bits.TrailingZeros64(fixed)), b)))
}
// Similar to add, but computes the Len of the limit for bitsize b.
func (l limit) bitlen(b uint) limit {
return noLimit.unsignedMinMax(
uint64(bits.Len64(l.umin)),
uint64(bits.Len64(l.umax)),
)
}
var noLimit = limit{math.MinInt64, math.MaxInt64, 0, math.MaxUint64}
// a limitFact is a limit known for a particular value.
@@ -1941,26 +1949,10 @@ func (ft *factsTable) flowLimit(v *Value) {
min := uint64(bits.OnesCount64(fixedBits))
ft.unsignedMinMax(v, min, min+changingBitsCount)
case OpBitLen64:
a := ft.limits[v.Args[0].ID]
ft.unsignedMinMax(v,
uint64(bits.Len64(a.umin)),
uint64(bits.Len64(a.umax)))
case OpBitLen32:
a := ft.limits[v.Args[0].ID]
ft.unsignedMinMax(v,
uint64(bits.Len32(uint32(a.umin))),
uint64(bits.Len32(uint32(a.umax))))
case OpBitLen16:
a := ft.limits[v.Args[0].ID]
ft.unsignedMinMax(v,
uint64(bits.Len16(uint16(a.umin))),
uint64(bits.Len16(uint16(a.umax))))
case OpBitLen8:
a := ft.limits[v.Args[0].ID]
ft.unsignedMinMax(v,
uint64(bits.Len8(uint8(a.umin))),
uint64(bits.Len8(uint8(a.umax))))
case OpBitLen64, OpBitLen32, OpBitLen16, OpBitLen8:
a := v.Args[0]
al := ft.limits[a.ID]
ft.newLimit(v, al.bitlen(uint(a.Type.Size())*8))
// Masks.

4
src/cmd/compile/internal/ssa/prove_test.go
View File

@@ -77,3 +77,7 @@ func TestLimitComUnsigned(t *testing.T) {
func TestLimitCtzUnsigned(t *testing.T) {
testLimitUnaryOpUnsigned8(t, "ctz", limit{-128, 127, 0, 8}, limit.ctz, func(x uint8) uint8 { return uint8(bits.TrailingZeros8(x)) })
}
func TestLimitBitlenUnsigned(t *testing.T) {
testLimitUnaryOpUnsigned8(t, "bitlen", limit{-128, 127, 0, 8}, limit.bitlen, func(x uint8) uint8 { return uint8(bits.Len8(x)) })
}