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cmd/compile: in poset, make constant handling more flexible

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Currently, constants in posets, in addition to being stored in
a DAG, are also stored as SSA values in a slice. This allows to
quickly go through all stored constants, but it's not easy to search
for a specific constant.

Following CLs will benefit from being able to quickly find
a constants by value in the poset, so change the constants
structure to a map. Since we're at it, don't store it as
*ssa.Value: poset always uses dense uint32 indices when
referring a node, so just switch to it.

Using a map also forces us to have a single node per
constant value: this is a good thing in the first place,
so this CL also make sure we never create two nodes for
the same constant value.

Change-Id: I099814578af35f935ebf14bc4767d607021f5f8b
Reviewed-on: https://go-review.googlesource.com/c/go/+/196781
Run-TryBot: Giovanni Bajo <rasky@develer.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>
This commit is contained in:
Giovanni Bajo 2019-09-22 01:26:50 +02:00
parent 50f1157760
commit c3a871fde1
1 changed files with 99 additions and 62 deletions
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161
src/cmd/compile/internal/ssa/poset.go
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@ -42,16 +42,17 @@ func (bs bitset) Test(idx uint32) bool {
type undoType uint8
const (
undoInvalid undoType = iota
undoCheckpoint // a checkpoint to group undo passes
undoSetChl // change back left child of undo.idx to undo.edge
undoSetChr // change back right child of undo.idx to undo.edge
undoNonEqual // forget that SSA value undo.ID is non-equal to undo.idx (another ID)
undoNewNode // remove new node created for SSA value undo.ID
undoAliasNode // unalias SSA value undo.ID so that it points back to node index undo.idx
undoNewRoot // remove node undo.idx from root list
undoChangeRoot // remove node undo.idx from root list, and put back undo.edge.Target instead
undoMergeRoot // remove node undo.idx from root list, and put back its children instead
undoInvalid undoType = iota
undoCheckpoint // a checkpoint to group undo passes
undoSetChl // change back left child of undo.idx to undo.edge
undoSetChr // change back right child of undo.idx to undo.edge
undoNonEqual // forget that SSA value undo.ID is non-equal to undo.idx (another ID)
undoNewNode // remove new node created for SSA value undo.ID
undoNewConstant // remove the constant node idx from the constants map
undoAliasNode // unalias SSA value undo.ID so that it points back to node index undo.idx
undoNewRoot // remove node undo.idx from root list
undoChangeRoot // remove node undo.idx from root list, and put back undo.edge.Target instead
undoMergeRoot // remove node undo.idx from root list, and put back its children instead
)
// posetUndo represents an undo pass to be performed.
@ -146,20 +147,20 @@ type posetNode struct {
// J K
//
type poset struct {
lastidx uint32 // last generated dense index
flags uint8 // internal flags
values map[ID]uint32 // map SSA values to dense indexes
constants []*Value // record SSA constants together with their value
nodes []posetNode // nodes (in all DAGs)
roots []uint32 // list of root nodes (forest)
noneq map[ID]bitset // non-equal relations
undo []posetUndo // undo chain
lastidx uint32 // last generated dense index
flags uint8 // internal flags
values map[ID]uint32 // map SSA values to dense indexes
constants map[int64]uint32 // record SSA constants together with their value
nodes []posetNode // nodes (in all DAGs)
roots []uint32 // list of root nodes (forest)
noneq map[ID]bitset // non-equal relations
undo []posetUndo // undo chain
}
func newPoset() *poset {
return &poset{
values: make(map[ID]uint32),
constants: make([]*Value, 0, 8),
constants: make(map[int64]uint32, 8),
nodes: make([]posetNode, 1, 16),
roots: make([]uint32, 0, 4),
noneq: make(map[ID]bitset),
@ -205,6 +206,11 @@ func (po *poset) upushalias(id ID, i2 uint32) {
po.undo = append(po.undo, posetUndo{typ: undoAliasNode, ID: id, idx: i2})
}
// upushconst pushes a new undo pass for a new constant
func (po *poset) upushconst(idx uint32, old uint32) {
po.undo = append(po.undo, posetUndo{typ: undoNewConstant, idx: idx, ID: ID(old)})
}
// addchild adds i2 as direct child of i1.
func (po *poset) addchild(i1, i2 uint32, strict bool) {
i1l, i1r := po.children(i1)
@ -281,18 +287,33 @@ func (po *poset) newconst(n *Value) {
panic("newconst on non-constant")
}
// If this is the first constant, put it into a new root, as
// If the same constant is already present in the poset through a different
// Value, just alias to it without allocating a new node.
val := n.AuxInt
if po.flags&posetFlagUnsigned != 0 {
val = int64(n.AuxUnsigned())
}
if c, found := po.constants[val]; found {
po.values[n.ID] = c
po.upushalias(n.ID, 0)
return
}
// Create the new node for this constant
i := po.newnode(n)
// If this is the first constant, put it as a new root, as
// we can't record an existing connection so we don't have
// a specific DAG to add it to. Notice that we want all
// constants to be in root #0, so make sure the new root
// goes there.
if len(po.constants) == 0 {
idx := len(po.roots)
i := po.newnode(n)
po.roots = append(po.roots, i)
po.roots[0], po.roots[idx] = po.roots[idx], po.roots[0]
po.upush(undoNewRoot, i, 0)
po.constants = append(po.constants, n)
po.constants[val] = i
po.upushconst(i, 0)
return
}
@ -301,21 +322,20 @@ func (po *poset) newconst(n *Value) {
// and the lower constant that is higher.
// The loop is duplicated to handle signed and unsigned comparison,
// depending on how the poset was configured.
var lowerptr, higherptr *Value
var lowerptr, higherptr uint32
if po.flags&posetFlagUnsigned != 0 {
var lower, higher uint64
val1 := n.AuxUnsigned()
for _, ptr := range po.constants {
val2 := ptr.AuxUnsigned()
for val2, ptr := range po.constants {
val2 := uint64(val2)
if val1 == val2 {
po.aliasnode(ptr, n)
return
panic("unreachable")
}
if val2 < val1 && (lowerptr == nil || val2 > lower) {
if val2 < val1 && (lowerptr == 0 || val2 > lower) {
lower = val2
lowerptr = ptr
} else if val2 > val1 && (higherptr == nil || val2 < higher) {
} else if val2 > val1 && (higherptr == 0 || val2 < higher) {
higher = val2
higherptr = ptr
}
@ -323,23 +343,21 @@ func (po *poset) newconst(n *Value) {
} else {
var lower, higher int64
val1 := n.AuxInt
for _, ptr := range po.constants {
val2 := ptr.AuxInt
for val2, ptr := range po.constants {
if val1 == val2 {
po.aliasnode(ptr, n)
return
panic("unreachable")
}
if val2 < val1 && (lowerptr == nil || val2 > lower) {
if val2 < val1 && (lowerptr == 0 || val2 > lower) {
lower = val2
lowerptr = ptr
} else if val2 > val1 && (higherptr == nil || val2 < higher) {
} else if val2 > val1 && (higherptr == 0 || val2 < higher) {
higher = val2
higherptr = ptr
}
}
}
if lowerptr == nil && higherptr == nil {
if lowerptr == 0 && higherptr == 0 {
// This should not happen, as at least one
// other constant must exist if we get here.
panic("no constant found")
@ -350,18 +368,17 @@ func (po *poset) newconst(n *Value) {
// of them, depending on what other constants are present in the poset.
// Notice that we always link constants together, so they
// are always part of the same DAG.
i := po.newnode(n)
switch {
case lowerptr != nil && higherptr != nil:
case lowerptr != 0 && higherptr != 0:
// Both bounds are present, record lower < n < higher.
po.addchild(po.values[lowerptr.ID], i, true)
po.addchild(i, po.values[higherptr.ID], true)
po.addchild(lowerptr, i, true)
po.addchild(i, higherptr, true)
case lowerptr != nil:
case lowerptr != 0:
// Lower bound only, record lower < n.
po.addchild(po.values[lowerptr.ID], i, true)
po.addchild(lowerptr, i, true)
case higherptr != nil:
case higherptr != 0:
// Higher bound only. To record n < higher, we need
// a dummy root:
//
@ -373,7 +390,7 @@ func (po *poset) newconst(n *Value) {
// \ /
// higher
//
i2 := po.values[higherptr.ID]
i2 := higherptr
r2 := po.findroot(i2)
if r2 != po.roots[0] { // all constants should be in root #0
panic("constant not in root #0")
@ -386,7 +403,8 @@ func (po *poset) newconst(n *Value) {
po.addchild(i, i2, true)
}
po.constants = append(po.constants, n)
po.constants[val] = i
po.upushconst(i, 0)
}
// aliasnode records that n2 is an alias of n1
@ -422,6 +440,19 @@ func (po *poset) aliasnode(n1, n2 *Value) {
po.upushalias(k, i2)
}
}
if n2.isGenericIntConst() {
val := n2.AuxInt
if po.flags&posetFlagUnsigned != 0 {
val = int64(n2.AuxUnsigned())
}
if po.constants[val] != i2 {
panic("aliasing constant which is not registered")
}
po.constants[val] = i1
po.upushconst(i1, i2)
}
} else {
// n2.ID wasn't seen before, so record it as alias to i1
po.values[n2.ID] = i1
@ -631,11 +662,7 @@ func (po *poset) CheckIntegrity() {
// Record which index is a constant
constants := newBitset(int(po.lastidx + 1))
for _, c := range po.constants {
if idx, ok := po.values[c.ID]; !ok {
panic("node missing for constant")
} else {
constants.Set(idx)
}
constants.Set(c)
}
// Verify that each node appears in a single DAG, and that
@ -732,15 +759,10 @@ func (po *poset) DotDump(fn string, title string) error {
names[i] = s
}
// Create constant mapping
// Create reverse constant mapping
consts := make(map[uint32]int64)
for _, v := range po.constants {
idx := po.values[v.ID]
if po.flags&posetFlagUnsigned != 0 {
consts[idx] = int64(v.AuxUnsigned())
} else {
consts[idx] = v.AuxInt
}
for val, idx := range po.constants {
consts[idx] = val
}
fmt.Fprintf(f, "digraph poset {\n")
@ -1171,10 +1193,25 @@ func (po *poset) Undo() {
po.nodes = po.nodes[:pass.idx]
po.lastidx--
// If it was the last inserted constant, remove it
nc := len(po.constants)
if nc > 0 && po.constants[nc-1].ID == pass.ID {
po.constants = po.constants[:nc-1]
case undoNewConstant:
// FIXME: remove this O(n) loop
var val int64
var i uint32
for val, i = range po.constants {
if i == pass.idx {
break
}
}
if i != pass.idx {
panic("constant not found in undo pass")
}
if pass.ID == 0 {
delete(po.constants, val)
} else {
// Restore previous index as constant node
// (also restoring the invariant on correct bounds)
oldidx := uint32(pass.ID)
po.constants[val] = oldidx
}
case undoAliasNode: