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cmd/compile: cleanup noLimit in prove

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- make it immutable
- calculate it rather than using hardcoded value
  (it all is inlined and constant folded away into noLimit's callers)

Change-Id: Ica12442df4d03e99123e62c0fe561c1078e35d75
Reviewed-on: https://go-review.googlesource.com/c/go/+/727181
Auto-Submit: Jorropo <jorropo.pgm@gmail.com>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
This commit is contained in:
Jorropo
2025-12-07 04:08:28 +01:00
committed by Gopher Robot
parent f35fb95503
commit 8f739162e6
1 changed files with 17 additions and 15 deletions
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32
src/cmd/compile/internal/ssa/prove.go
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@@ -250,6 +250,10 @@ func fitsInBitsU(x uint64, b uint) bool {
return x>>b == 0
}
func noLimit() limit {
return noLimitForBitsize(64)
}
func noLimitForBitsize(bitsize uint) limit {
return limit{min: -(1 << (bitsize - 1)), max: 1<<(bitsize-1) - 1, umin: 0, umax: 1<<bitsize - 1}
}
@@ -302,7 +306,7 @@ func (l limit) add(l2 limit, b uint) limit {
return limit{min: int64r, max: int64r, umin: r, umax: r}
}
r := noLimit
r := noLimit()
min, minOk := safeAdd(l.min, l2.min, b)
max, maxOk := safeAdd(l.max, l2.max, b)
if minOk && maxOk {
@@ -320,7 +324,7 @@ func (l limit) add(l2 limit, b uint) limit {
// same as add but for subtraction.
func (l limit) sub(l2 limit, b uint) limit {
r := noLimit
r := noLimit()
min, minOk := safeSub(l.min, l2.max, b)
max, maxOk := safeSub(l.max, l2.min, b)
if minOk && maxOk {
@@ -338,7 +342,7 @@ func (l limit) sub(l2 limit, b uint) limit {
// same as add but for multiplication.
func (l limit) mul(l2 limit, b uint) limit {
r := noLimit
r := noLimit()
umaxhi, umaxlo := bits.Mul64(l.umax, l2.umax)
if umaxhi == 0 && fitsInBitsU(umaxlo, b) {
r.umax = umaxlo
@@ -360,7 +364,7 @@ func (l limit) mul(l2 limit, b uint) limit {
// Similar to add, but compute 1 << l if it fits without overflow in b bits.
func (l limit) exp2(b uint) limit {
r := noLimit
r := noLimit()
if l.umax < uint64(b) {
r.umin = 1 << l.umin
r.umax = 1 << l.umax
@@ -423,14 +427,14 @@ func (l limit) ctz(b uint) limit {
if l.umin&((1<<varying)-1) != 0 {
// there will always be at least one non-zero bit in the varying part
varying--
return noLimit.unsignedMax(uint64(varying))
return noLimit().unsignedMax(uint64(varying))
}
return noLimit.unsignedMax(uint64(min(uint(bits.TrailingZeros64(fixed)), b)))
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(
return noLimit().unsignedMinMax(
uint64(bits.Len64(l.umin)),
uint64(bits.Len64(l.umax)),
)
@@ -456,11 +460,9 @@ func (l limit) popcount(b uint) limit {
min++
}
return noLimit.unsignedMinMax(min, max)
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.
type limitFact struct {
vid ID
@@ -611,7 +613,7 @@ func (ft *factsTable) pointerNil(v *Value) {
ft.newLimit(v, limit{min: 0, max: 0, umin: 0, umax: 0})
}
func (ft *factsTable) pointerNonNil(v *Value) {
l := noLimit
l := noLimit()
l.umin = 1
ft.newLimit(v, l)
}
@@ -1843,15 +1845,15 @@ func initLimit(v *Value) limit {
case OpConstNil:
return limit{min: 0, max: 0, umin: 0, umax: 0}
case OpAddr, OpLocalAddr: // TODO: others?
l := noLimit
l := noLimit()
l.umin = 1
return l
default:
return noLimit
return noLimit()
}
}
if !v.Type.IsInteger() {
return noLimit
return noLimit()
}
// Default limits based on type.
@@ -2063,7 +2065,7 @@ func (ft *factsTable) flowLimit(v *Value) {
case OpDiv64u, OpDiv32u, OpDiv16u, OpDiv8u:
a := ft.limits[v.Args[0].ID]
b := ft.limits[v.Args[1].ID]
lim := noLimit
lim := noLimit()
if b.umax > 0 {
lim = lim.unsignedMin(a.umin / b.umax)
}