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[dev.ssa] cmd/compile/internal/ssa: factor out copyelimValue and phielimValue
* Merge copyelim into phielim. * Add phielimValue to rewrite. cgoIsGoPointer is, for example, 2 instructions smaller now. Change-Id: I8baeb206d1b3ef8aba4a6e3bcdc432959bcae2d5 Reviewed-on: https://go-review.googlesource.com/19462 Reviewed-by: David Chase <drchase@google.com>
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@ -8,15 +8,7 @@ package ssa
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func copyelim(f *Func) {
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for _, b := range f.Blocks {
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for _, v := range b.Values {
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for i, w := range v.Args {
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x := w
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for x.Op == OpCopy {
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x = x.Args[0]
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}
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if x != w {
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v.Args[i] = x
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}
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}
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copyelimValue(v)
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}
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v := b.Control
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if v != nil {
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@ -41,3 +33,28 @@ func copyelim(f *Func) {
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}
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}
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}
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func copyelimValue(v *Value) {
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// elide any copies generated during rewriting
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for i, a := range v.Args {
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if a.Op != OpCopy {
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continue
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}
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// Rewriting can generate OpCopy loops.
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// They are harmless (see removePredecessor),
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// but take care to stop if we find a cycle.
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slow := a // advances every other iteration
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var advance bool
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for a.Op == OpCopy {
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a = a.Args[0]
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if slow == a {
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break
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}
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if advance {
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slow = slow.Args[0]
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}
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advance = !advance
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}
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v.Args[i] = a
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}
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}
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@ -18,44 +18,47 @@ package ssa
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// and would that be useful?
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func phielim(f *Func) {
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for {
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changed := false
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change := false
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for _, b := range f.Blocks {
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nextv:
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for _, v := range b.Values {
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if v.Op != OpPhi {
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continue
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}
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// If there are two distinct args of v which
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// are not v itself, then the phi must remain.
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// Otherwise, we can replace it with a copy.
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var w *Value
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for _, x := range v.Args {
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for x.Op == OpCopy {
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x = x.Args[0]
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}
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if x == v {
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continue
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}
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if x == w {
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continue
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}
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if w != nil {
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continue nextv
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}
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w = x
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}
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if w == nil {
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// v references only itself. It must be in
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// a dead code loop. Don't bother modifying it.
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continue
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}
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v.Op = OpCopy
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v.SetArgs1(w)
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changed = true
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copyelimValue(v)
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change = phielimValue(v) || change
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}
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}
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if !changed {
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if !change {
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break
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}
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}
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}
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func phielimValue(v *Value) bool {
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if v.Op != OpPhi {
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return false
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}
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// If there are two distinct args of v which
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// are not v itself, then the phi must remain.
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// Otherwise, we can replace it with a copy.
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var w *Value
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for _, x := range v.Args {
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if x == v {
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continue
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}
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if x == w {
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continue
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}
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if w != nil {
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return false
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}
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w = x
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}
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if w == nil {
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// v references only itself. It must be in
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// a dead code loop. Don't bother modifying it.
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return false
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}
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v.Op = OpCopy
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v.SetArgs1(w)
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return true
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}
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@ -40,28 +40,8 @@ func applyRewrite(f *Func, rb func(*Block) bool, rv func(*Value, *Config) bool)
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}
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curb = nil
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for _, v := range b.Values {
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// elide any copies generated during rewriting
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for i, a := range v.Args {
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if a.Op != OpCopy {
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continue
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}
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// Rewriting can generate OpCopy loops.
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// They are harmless (see removePredecessor),
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// but take care to stop if we find a cycle.
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slow := a // advances every other iteration
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var advance bool
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for a.Op == OpCopy {
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a = a.Args[0]
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if slow == a {
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break
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}
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if advance {
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slow = a
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}
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advance = !advance
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}
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v.Args[i] = a
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}
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copyelimValue(v)
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change = phielimValue(v) || change
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// apply rewrite function
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curv = v
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