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cmd/compile: fold IsInBounds of modulo.

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In b we only need the division by 0 check.

func b(i uint, v []byte) byte {
    return v[i%uint(len(v))]
}

Updates #15079.

Change-Id: Ic7491e677dd57cd6ba577efbce576dbb6e023cbd
Reviewed-on: https://go-review.googlesource.com/21502
Run-TryBot: Alexandru Moșoi <alexandru@mosoi.ro>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Ahmed Waheed <oneofone@gmail.com>
This commit is contained in:
Alexandru Moșoi 2016-04-04 16:38:26 +02:00 committed by Alexandru Moșoi
parent 61f56e925e
commit 68325b56e7
3 changed files with 85 additions and 1 deletions
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49
src/cmd/compile/internal/gc/testdata/divbyzero_ssa.go vendored Normal file
View file

@ -0,0 +1,49 @@
package main
import (
"fmt"
"runtime"
)
var failed = false
func checkDivByZero(f func()) (divByZero bool) {
defer func() {
if r := recover(); r != nil {
if e, ok := r.(runtime.Error); ok && e.Error() == "runtime error: integer divide by zero" {
divByZero = true
}
}
}()
f()
return false
}
//go:noinline
func a(i uint, s []int) int {
return s[i%uint(len(s))]
}
//go:noinline
func b(i uint, j uint) uint {
return i / j
}
func main() {
if got := checkDivByZero(func() { b(7, 0) }); !got {
fmt.Printf("expected div by zero for b(7, 0), got no error\n")
failed = true
}
if got := checkDivByZero(func() { b(7, 7) }); got {
fmt.Printf("expected no error for b(7, 7), got div by zero\n")
failed = true
}
if got := checkDivByZero(func() { a(4, nil) }); !got {
fmt.Printf("expected div by zero for a(4, nil), got no error\n")
failed = true
}
if failed {
panic("tests failed")
}
}

5
src/cmd/compile/internal/ssa/gen/generic.rules
View file

@ -109,12 +109,15 @@
(IsInBounds (ZeroExt8to64 _) (Const64 [c])) && (1 << 8) <= c -> (ConstBool [1])
(IsInBounds (ZeroExt16to32 _) (Const32 [c])) && (1 << 16) <= c -> (ConstBool [1])
(IsInBounds (ZeroExt16to64 _) (Const64 [c])) && (1 << 16) <= c -> (ConstBool [1])
(IsInBounds x x) -> (ConstBool [0])
(IsInBounds (And32 (Const32 [c]) _) (Const32 [d])) && 0 <= c && c < d -> (ConstBool [1])
(IsInBounds (And64 (Const64 [c]) _) (Const64 [d])) && 0 <= c && c < d -> (ConstBool [1])
(IsInBounds (Const32 [c]) (Const32 [d])) -> (ConstBool [b2i(0 <= c && c < d)])
(IsInBounds (Const64 [c]) (Const64 [d])) -> (ConstBool [b2i(0 <= c && c < d)])
// (Mod64u x y) is always between 0 (inclusive) and y (exclusive).
(IsInBounds (Mod32u _ y) y) -> (ConstBool [1])
(IsInBounds (Mod64u _ y) y) -> (ConstBool [1])
(IsSliceInBounds x x) -> (ConstBool [1])
(IsSliceInBounds (And32 (Const32 [c]) _) (Const32 [d])) && 0 <= c && c <= d -> (ConstBool [1])
(IsSliceInBounds (And64 (Const64 [c]) _) (Const64 [d])) && 0 <= c && c <= d -> (ConstBool [1])

32
src/cmd/compile/internal/ssa/rewritegeneric.go
View file

@ -2815,6 +2815,38 @@ func rewriteValuegeneric_OpIsInBounds(v *Value, config *Config) bool {
v.AuxInt = b2i(0 <= c && c < d)
return true
}
// match: (IsInBounds (Mod32u _ y) y)
// cond:
// result: (ConstBool [1])
for {
v_0 := v.Args[0]
if v_0.Op != OpMod32u {
break
}
y := v_0.Args[1]
if y != v.Args[1] {
break
}
v.reset(OpConstBool)
v.AuxInt = 1
return true
}
// match: (IsInBounds (Mod64u _ y) y)
// cond:
// result: (ConstBool [1])
for {
v_0 := v.Args[0]
if v_0.Op != OpMod64u {
break
}
y := v_0.Args[1]
if y != v.Args[1] {
break
}
v.reset(OpConstBool)
v.AuxInt = 1
return true
}
return false
}
func rewriteValuegeneric_OpIsSliceInBounds(v *Value, config *Config) bool {