cmd/compile: cleanup noLimit in prove

- 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>

diff --git a/src/cmd/compile/internal/ssa/prove.go b/src/cmd/compile/internal/ssa/prove.go
index 3de964f06127dfde9d59d62cf88db5d641e68fbe..c9f75daa67207acb8cba641ba8c03a7024a224f3 100644 (file)
--- a/src/cmd/compile/internal/ssa/prove.go
+++ b/src/cmd/compile/internal/ssa/prove.go
@@ -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)
                }