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perf: reduce allocations in the printer and string-list sorting #1476

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perf: reduce allocations in the printer and string-list sorting #1476

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19 changes: 13 additions & 6 deletions build/print.go
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Original file line number Diff line number Diff line change
Expand Up @@ -1032,12 +1032,19 @@ func (p *printer) useCompactMode(start *Position, list *[]Expr, end *End, mode s
// If multiLine is true, seq avoids the compact form even
// for 0- and 1-element sequences.
func (p *printer) seq(brack string, start *Position, list *[]Expr, end *End, mode seqMode, forceCompact, forceMultiLine bool) {
args := &[]Expr{}
for _, x := range *list {
// nil arguments may be added by some linter checks, filter them out because
// they may cause NPE.
if x != nil {
*args = append(*args, x)
// Filter out nil arguments (rare; added by some linter checks) that may cause a NPE, copying only if needed.
args := list
for i, x := range *list {
if x == nil {
filtered := make([]Expr, i, len(*list))
copy(filtered, (*list)[:i])
for _, y := range (*list)[i+1:] {
if y != nil {
filtered = append(filtered, y)
}
}
args = &filtered
break
}
}
Comment on lines +1036 to 1049

@gemini-code-assist gemini-code-assist Bot Jun 10, 2026

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medium

When a nil element is found, we can optimize the filtering process by avoiding a full second pass over the entire slice. Instead, we can create the filtered slice with a length equal to the index i of the first nil element, use the highly optimized built-in copy function to copy the non-nil prefix, and then only loop over the remaining elements starting from i+1. Ensure that this optimization is consistent with the previous behavior and does not introduce any unintended side effects.

Suggested change
args := list
for _, x := range *list {
// nil arguments may be added by some linter checks, filter them out because
// they may cause NPE.
if x != nil {
*args = append(*args, x)
if x == nil {
filtered := make([]Expr, 0, len(*list))
for _, y := range *list {
if y != nil {
filtered = append(filtered, y)
}
}
args = &filtered
break
}
}
args := list
for i, x := range *list {
if x == nil {
filtered := make([]Expr, i, len(*list))
copy(filtered, (*list)[:i])
for _, y := range (*list)[i+1:] {
if y != nil {
filtered = append(filtered, y)
}
}
args = &filtered
break
}
}
References
  1. When modifying code, ensure that changes are consistent with previous behavior, especially if the previous behavior was intentional.


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