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[dev.ssa] cmd/compile: implement OSLICESTR

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Add a new function and generic operation to handle
bounds checking for slices. Unlike the index
bounds checking the index can be equal to the upper
bound.

Do gc-friendly slicing that generates proper code for
0-length result slices.

This is a takeover of Alexandru's original change,
(https://go-review.googlesource.com/#/c/12764/)
submittable now that the decompose phase is in.

Change-Id: I17d164cf42ed7839f84ca949c6ad3289269c9160
Reviewed-on: https://go-review.googlesource.com/13903
Reviewed-by: David Chase <drchase@google.com>
This commit is contained in:
Keith Randall 2015-08-24 23:52:03 -07:00 committed by David Chase
parent 8e601b23cd
commit 3526cf586b
6 changed files with 234 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

86
src/cmd/compile/internal/gc/ssa.go
View File

@ -1465,6 +1465,71 @@ func (s *state) expr(n *Node) *ssa.Value {
a := s.expr(n.Left)
return s.newValue1(ssa.OpITab, n.Type, a)
case OSLICESTR:
// Evaluate the string once.
str := s.expr(n.Left)
ptr := s.newValue1(ssa.OpStringPtr, Ptrto(Types[TUINT8]), str)
len := s.newValue1(ssa.OpStringLen, Types[TINT], str)
zero := s.constInt(Types[TINT], 0)
// Evaluate the slice indexes.
var low, high *ssa.Value
if n.Right.Left == nil {
low = zero
} else {
low = s.expr(n.Right.Left)
}
if n.Right.Right == nil {
high = len
} else {
high = s.expr(n.Right.Right)
}
// Panic if slice indices are not in bounds.
s.sliceBoundsCheck(low, high)
s.sliceBoundsCheck(high, len)
// Generate the following code assuming that indexes are in bounds.
// The conditional is to make sure that we don't generate a string
// that points to the next object in memory.
// rlen = (SubPtr high low)
// p = ptr
// if rlen != 0 {
// p = (AddPtr ptr low)
// }
// result = (StringMake p size)
rlen := s.newValue2(ssa.OpSubPtr, Types[TINT], high, low)
// Use n as the "variable" for p.
s.vars[n] = ptr
// Generate code to test the resulting slice length.
var cmp *ssa.Value
if s.config.IntSize == 8 {
cmp = s.newValue2(ssa.OpNeq64, Types[TBOOL], rlen, zero)
} else {
cmp = s.newValue2(ssa.OpNeq32, Types[TBOOL], rlen, zero)
}
b := s.endBlock()
b.Kind = ssa.BlockIf
b.Likely = ssa.BranchLikely
b.Control = cmp
// Generate code for non-zero length slice case.
nz := s.f.NewBlock(ssa.BlockPlain)
addEdge(b, nz)
s.startBlock(nz)
s.vars[n] = s.newValue2(ssa.OpAddPtr, Ptrto(Types[TUINT8]), ptr, low)
s.endBlock()
// All done.
merge := s.f.NewBlock(ssa.BlockPlain)
addEdge(b, merge)
addEdge(nz, merge)
s.startBlock(merge)
return s.newValue2(ssa.OpStringMake, Types[TSTRING], s.variable(n, Ptrto(Types[TUINT8])), rlen)
case OCALLFUNC, OCALLMETH:
left := n.Left
static := left.Op == ONAME && left.Class == PFUNC
@ -1782,6 +1847,25 @@ func (s *state) boundsCheck(idx, len *ssa.Value) {
// bounds check
cmp := s.newValue2(ssa.OpIsInBounds, Types[TBOOL], idx, len)
s.check(cmp, ssa.OpPanicIndexCheck)
}
// sliceBoundsCheck generates slice bounds checking code. Checks if 0 <= idx <= len, branches to exit if not.
// Starts a new block on return.
func (s *state) sliceBoundsCheck(idx, len *ssa.Value) {
if Debug['B'] != 0 {
return
}
// TODO: convert index to full width?
// TODO: if index is 64-bit and we're compiling to 32-bit, check that high 32 bits are zero.
// bounds check
cmp := s.newValue2(ssa.OpIsSliceInBounds, Types[TBOOL], idx, len)
s.check(cmp, ssa.OpPanicSliceCheck)
}
// If cmp (a bool) is true, panic using the given op.
func (s *state) check(cmp *ssa.Value, panicOp ssa.Op) {
b := s.endBlock()
b.Kind = ssa.BlockIf
b.Control = cmp
@ -1794,7 +1878,7 @@ func (s *state) boundsCheck(idx, len *ssa.Value) {
s.startBlock(bPanic)
// The panic check takes/returns memory to ensure that the right
// memory state is observed if the panic happens.
s.vars[&memvar] = s.newValue1(ssa.OpPanicIndexCheck, ssa.TypeMem, s.mem())
s.vars[&memvar] = s.newValue1(panicOp, ssa.TypeMem, s.mem())
s.endBlock()
s.startBlock(bNext)
}

92
src/cmd/compile/internal/gc/testdata/string_ssa.go vendored Normal file
View File

@ -0,0 +1,92 @@
// string_ssa.go tests string operations.
package main
var failed = false
func testStringSlice1_ssa(a string, i, j int) string {
switch { // prevent inlining
}
return a[i:]
}
func testStringSlice2_ssa(a string, i, j int) string {
switch { // prevent inlining
}
return a[:j]
}
func testStringSlice12_ssa(a string, i, j int) string {
switch { // prevent inlining
}
return a[i:j]
}
func testStringSlice() {
tests := [...]struct {
fn func(string, int, int) string
s string
low, high int
want string
}{
// -1 means the value is not used.
{testStringSlice1_ssa, "foobar", 0, -1, "foobar"},
{testStringSlice1_ssa, "foobar", 3, -1, "bar"},
{testStringSlice1_ssa, "foobar", 6, -1, ""},
{testStringSlice2_ssa, "foobar", -1, 0, ""},
{testStringSlice2_ssa, "foobar", -1, 3, "foo"},
{testStringSlice2_ssa, "foobar", -1, 6, "foobar"},
{testStringSlice12_ssa, "foobar", 0, 6, "foobar"},
{testStringSlice12_ssa, "foobar", 0, 0, ""},
{testStringSlice12_ssa, "foobar", 6, 6, ""},
{testStringSlice12_ssa, "foobar", 1, 5, "ooba"},
{testStringSlice12_ssa, "foobar", 3, 3, ""},
{testStringSlice12_ssa, "", 0, 0, ""},
}
for i, t := range tests {
if got := t.fn(t.s, t.low, t.high); t.want != got {
println("#", i, " ", t.s, "[", t.low, ":", t.high, "] = ", got, " want ", t.want)
failed = true
}
}
}
type prefix struct {
prefix string
}
func (p *prefix) slice_ssa() {
p.prefix = p.prefix[:3]
}
func testStructSlice() {
switch {
}
p := &prefix{"prefix"}
p.slice_ssa()
if "pre" != p.prefix {
println("wrong field slice: wanted %s got %s", "pre", p.prefix)
}
}
func testStringSlicePanic() {
defer func() {
if r := recover(); r != nil {
println("paniced as expected")
}
}()
str := "foobar"
println("got ", testStringSlice12_ssa(str, 3, 9))
println("expected to panic, but didn't")
failed = true
}
func main() {
testStringSlice()
testStringSlicePanic()
if failed {
panic("failed")
}
}

2
src/cmd/compile/internal/ssa/gen/AMD64.rules
View File

@ -19,6 +19,7 @@
(Add64F x y) -> (ADDSD x y)
(Sub64 x y) -> (SUBQ x y)
(SubPtr x y) -> (SUBQ x y)
(Sub32 x y) -> (SUBL x y)
(Sub16 x y) -> (SUBW x y)
(Sub8 x y) -> (SUBB x y)
@ -279,6 +280,7 @@
// checks
(IsNonNil p) -> (SETNE (TESTQ <TypeFlags> p p))
(IsInBounds idx len) -> (SETB (CMPQ <TypeFlags> idx len))
(IsSliceInBounds idx len) -> (SETBE (CMPQ <TypeFlags> idx len))
(PanicNilCheck ptr mem) -> (LoweredPanicNilCheck ptr mem)
(PanicIndexCheck mem) -> (LoweredPanicIndexCheck mem)

7
src/cmd/compile/internal/ssa/gen/genericOps.go
View File

@ -21,9 +21,11 @@ var genericOps = []opData{
{name: "Sub16"},
{name: "Sub32"},
{name: "Sub64"},
{name: "SubPtr"},
{name: "Sub32F"},
{name: "Sub64F"},
// TODO: Sub64C, Sub128C
// TODO: Sub32F, Sub64F, Sub64C, Sub128C
{name: "Mul8"}, // arg0 * arg1
{name: "Mul16"},
@ -311,8 +313,9 @@ var genericOps = []opData{
{name: "Cvt64Fto32F"},
// Automatically inserted safety checks
{name: "IsNonNil"}, // arg0 != nil
{name: "IsInBounds"}, // 0 <= arg0 < arg1
{name: "IsNonNil"}, // arg0 != nil
{name: "IsInBounds"}, // 0 <= arg0 < arg1
{name: "IsSliceInBounds"}, // 0 <= arg0 <= arg1
// Pseudo-ops
{name: "PanicNilCheck"}, // trigger a dereference fault; arg0=nil ptr, arg1=mem, returns mem

12
src/cmd/compile/internal/ssa/opGen.go
View File

@ -274,6 +274,7 @@ const (
OpSub16
OpSub32
OpSub64
OpSubPtr
OpSub32F
OpSub64F
OpMul8
@ -491,6 +492,7 @@ const (
OpCvt64Fto32F
OpIsNonNil
OpIsInBounds
OpIsSliceInBounds
OpPanicNilCheck
OpPanicIndexCheck
OpPanicSliceCheck
@ -2335,6 +2337,7 @@ var opcodeTable = [...]opInfo{
inputs: []inputInfo{
{0, 65535}, // .AX .CX .DX .BX .SP .BP .SI .DI .R8 .R9 .R10 .R11 .R12 .R13 .R14 .R15
},
clobbers: 8589934592, // .FLAGS
outputs: []regMask{
65519, // .AX .CX .DX .BX .BP .SI .DI .R8 .R9 .R10 .R11 .R12 .R13 .R14 .R15
},
@ -2631,7 +2634,6 @@ var opcodeTable = [...]opInfo{
inputs: []inputInfo{
{0, 65535}, // .AX .CX .DX .BX .SP .BP .SI .DI .R8 .R9 .R10 .R11 .R12 .R13 .R14 .R15
},
clobbers: 8589934592, // .FLAGS
outputs: []regMask{
65519, // .AX .CX .DX .BX .BP .SI .DI .R8 .R9 .R10 .R11 .R12 .R13 .R14 .R15
},
@ -3106,6 +3108,10 @@ var opcodeTable = [...]opInfo{
name: "Sub64",
generic: true,
},
{
name: "SubPtr",
generic: true,
},
{
name: "Sub32F",
generic: true,
@ -3974,6 +3980,10 @@ var opcodeTable = [...]opInfo{
name: "IsInBounds",
generic: true,
},
{
name: "IsSliceInBounds",
generic: true,
},
{
name: "PanicNilCheck",
generic: true,

39
src/cmd/compile/internal/ssa/rewriteAMD64.go
View File

@ -2791,6 +2791,27 @@ func rewriteValueAMD64(v *Value, config *Config) bool {
goto endff508c3726edfb573abc6128c177e76c
endff508c3726edfb573abc6128c177e76c:
;
case OpIsSliceInBounds:
// match: (IsSliceInBounds idx len)
// cond:
// result: (SETBE (CMPQ <TypeFlags> idx len))
{
idx := v.Args[0]
len := v.Args[1]
v.Op = OpAMD64SETBE
v.AuxInt = 0
v.Aux = nil
v.resetArgs()
v0 := b.NewValue0(v.Line, OpAMD64CMPQ, TypeInvalid)
v0.Type = TypeFlags
v0.AddArg(idx)
v0.AddArg(len)
v.AddArg(v0)
return true
}
goto end41f8211150e3a4ef36a1b5168013f96f
end41f8211150e3a4ef36a1b5168013f96f:
;
case OpLeq16:
// match: (Leq16 x y)
// cond:
@ -9579,6 +9600,24 @@ func rewriteValueAMD64(v *Value, config *Config) bool {
goto end7d33bf9bdfa505f96b930563eca7955f
end7d33bf9bdfa505f96b930563eca7955f:
;
case OpSubPtr:
// match: (SubPtr x y)
// cond:
// result: (SUBQ x y)
{
x := v.Args[0]
y := v.Args[1]
v.Op = OpAMD64SUBQ
v.AuxInt = 0
v.Aux = nil
v.resetArgs()
v.AddArg(x)
v.AddArg(y)
return true
}
goto end748f63f755afe0b97a8f3cf7e4d9cbfe
end748f63f755afe0b97a8f3cf7e4d9cbfe:
;
case OpTrunc16to8:
// match: (Trunc16to8 x)
// cond: