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cmd/compile: optimize lookupVarOutgoing
If b has exactly one predecessor, as happens frequently with static calls, we can make lookupVarOutgoing generate less garbage. Instead of generating a value that is just going to be an OpCopy and then get eliminated, loop. This can lead to lots of looping. However, this loop is way cheaper than generating lots of ssa.Values and then eliminating them. For a subset of the code in #15537: Before: 28.31 real 36.17 user 1.68 sys 2282450944 maximum resident set size After: 9.63 real 11.66 user 0.51 sys 638144512 maximum resident set size Updates #15537. Excitingly, it appears that this also helps regular code: name old time/op new time/op delta Template 288ms ± 6% 276ms ± 7% -4.13% (p=0.000 n=21+24) Unicode 143ms ± 8% 141ms ±10% ~ (p=0.287 n=24+25) GoTypes 932ms ± 4% 874ms ± 4% -6.20% (p=0.000 n=23+22) Compiler 4.89s ± 4% 4.58s ± 4% -6.46% (p=0.000 n=22+23) MakeBash 40.2s ±13% 39.8s ± 9% ~ (p=0.648 n=23+23) name old user-ns/op new user-ns/op delta Template 388user-ms ±10% 373user-ms ± 5% -3.80% (p=0.000 n=24+25) Unicode 203user-ms ± 6% 202user-ms ± 7% ~ (p=0.492 n=22+24) GoTypes 1.29user-s ± 4% 1.17user-s ± 4% -9.67% (p=0.000 n=25+23) Compiler 6.86user-s ± 5% 6.28user-s ± 4% -8.49% (p=0.000 n=25+25) name old alloc/op new alloc/op delta Template 51.5MB ± 0% 47.6MB ± 0% -7.47% (p=0.000 n=22+25) Unicode 37.2MB ± 0% 37.1MB ± 0% -0.21% (p=0.000 n=25+25) GoTypes 166MB ± 0% 138MB ± 0% -16.83% (p=0.000 n=25+25) Compiler 756MB ± 0% 628MB ± 0% -16.96% (p=0.000 n=25+23) name old allocs/op new allocs/op delta Template 450k ± 0% 445k ± 0% -1.02% (p=0.000 n=25+25) Unicode 356k ± 0% 356k ± 0% ~ (p=0.374 n=24+25) GoTypes 1.31M ± 0% 1.25M ± 0% -4.18% (p=0.000 n=25+25) Compiler 5.29M ± 0% 5.02M ± 0% -5.15% (p=0.000 n=25+23) It also seems to help in other cases in which phi insertion is a pain point (#14774, #14934). Change-Id: Ibd05ed7b99d262117ece7bb250dfa8c3d1cc5dd2 Reviewed-on: https://go-review.googlesource.com/22790 Reviewed-by: Keith Randall <khr@golang.org> Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
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@ -3832,15 +3832,22 @@ func (s *state) resolveFwdRef(v *ssa.Value) {
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// lookupVarOutgoing finds the variable's value at the end of block b.
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// lookupVarOutgoing finds the variable's value at the end of block b.
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func (s *state) lookupVarOutgoing(b *ssa.Block, t ssa.Type, name *Node, line int32) *ssa.Value {
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func (s *state) lookupVarOutgoing(b *ssa.Block, t ssa.Type, name *Node, line int32) *ssa.Value {
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m := s.defvars[b.ID]
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for {
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if v, ok := m[name]; ok {
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if v, ok := s.defvars[b.ID][name]; ok {
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return v
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return v
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}
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}
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// The variable is not defined by b and we haven't
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// The variable is not defined by b and we haven't looked it up yet.
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// looked it up yet. Generate a FwdRef for the variable and return that.
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// If b has exactly one predecessor, loop to look it up there.
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// Otherwise, give up and insert a new FwdRef and resolve it later.
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if len(b.Preds) != 1 {
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break
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}
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b = b.Preds[0].Block()
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}
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// Generate a FwdRef for the variable and return that.
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v := b.NewValue0A(line, ssa.OpFwdRef, t, name)
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v := b.NewValue0A(line, ssa.OpFwdRef, t, name)
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s.fwdRefs = append(s.fwdRefs, v)
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s.fwdRefs = append(s.fwdRefs, v)
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m[name] = v
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s.defvars[b.ID][name] = v
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s.addNamedValue(name, v)
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s.addNamedValue(name, v)
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return v
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return v
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}
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}
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