Stowage/go
2
0
Fork 0
mirror of https://github.com/golang/go.git synced 2025-12-08 06:10:04 +00:00
Code Issues Projects Releases Packages Wiki Activity

cmd/compile: compute Complement's limits from argument's limits

Browse source 
I was not sure this was correct so I exhaustively checked all possibilities:
https://go.dev/play/p/hjmCLm4Iagz
https://go.dev/play/p/R9RuRGKwCbN

Change-Id: I85f053df825a4d77f978de42f8a1fcaf4b881def
Reviewed-on: https://go-review.googlesource.com/c/go/+/605696
Reviewed-by: Keith Randall <khr@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>
This commit is contained in:
Jorropo 2024-08-14 22:28:00 +02:00 • committed by Keith Randall
parent 4f2c0e5d08
commit 2f3165973f
2 changed files with 60 additions and 0 deletions
Download patch file Download diff file Expand all files Collapse all files

39
src/cmd/compile/internal/ssa/prove.go
View file

@ -341,6 +341,42 @@ func (l limit) exp2(b uint) limit {
return r
}
// Similar to add, but computes the complement of the limit for bitsize b.
func (l limit) com(b uint) limit {
switch b {
case 64:
return limit{
min: ^l.max,
max: ^l.min,
umin: ^l.umax,
umax: ^l.umin,
}
case 32:
return limit{
min: int64(^int32(l.max)),
max: int64(^int32(l.min)),
umin: uint64(^uint32(l.umax)),
umax: uint64(^uint32(l.umin)),
}
case 16:
return limit{
min: int64(^int16(l.max)),
max: int64(^int16(l.min)),
umin: uint64(^uint16(l.umax)),
umax: uint64(^uint16(l.umin)),
}
case 8:
return limit{
min: int64(^int8(l.max)),
max: int64(^int8(l.min)),
umin: uint64(^uint8(l.umax)),
umax: uint64(^uint8(l.umin)),
}
default:
panic("unreachable")
}
}
var noLimit = limit{math.MinInt64, math.MaxInt64, 0, math.MaxUint64}
// a limitFact is a limit known for a particular value.
@ -1714,6 +1750,9 @@ func (ft *factsTable) flowLimit(v *Value) bool {
a := ft.limits[v.Args[0].ID]
b := ft.limits[v.Args[1].ID]
return ft.unsignedMax(v, 1<<bits.Len64(a.umax|b.umax)-1)
case OpCom64, OpCom32, OpCom16, OpCom8:
a := ft.limits[v.Args[0].ID]
return ft.newLimit(v, a.com(uint(v.Type.Size())*8))
// Arithmetic.
case OpAdd64: