From f00e7a4e15be6299166aa30045efbadb7d7c8423 Mon Sep 17 00:00:00 2001
From: Jake Waggoner <32466459+waggonerjake@users.noreply.github.com>
Date: Wed, 13 Oct 2021 18:12:20 -0400
Subject: [PATCH] perf: Only do memory allocation when zero coin is found
 (#10339)

## Description

Closes: #10333

Added a loop that checks for zero coins before making any memory allocations. If no zero coins are found, just return the `coins` slice as is. If a zero coin is found, then allocate the new array, stop looking for the first zero, and restart the loop to "remove" the 0's.

---

### Author Checklist

*All items are required. Please add a note to the item if the item is not applicable and
please add links to any relevant follow up issues.*

I have...

- [x] included the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title
- [ ] added `!` to the type prefix if API or client breaking change (Not Applicable)
- [x] targeted the correct branch (see [PR Targeting](https://github.com/cosmos/cosmos-sdk/blob/master/CONTRIBUTING.md#pr-targeting))
- [x] provided a link to the relevant issue or specification
- [ ] followed the guidelines for [building modules](https://github.com/cosmos/cosmos-sdk/blob/master/docs/building-modules) (Not Applicable)
- [ ] included the necessary unit and integration [tests](https://github.com/cosmos/cosmos-sdk/blob/master/CONTRIBUTING.md#testing) (Not Applicable)
- [x] added a changelog entry to `CHANGELOG.md`
- [ ] included comments for [documenting Go code](https://blog.golang.org/godoc) (Not Applicable)
- [ ] updated the relevant documentation or specification (Not Applicable)
- [x] reviewed "Files changed" and left comments if necessary
- [ ] confirmed all CI checks have passed

### Reviewers Checklist

*All items are required. Please add a note if the item is not applicable and please add
your handle next to the items reviewed if you only reviewed selected items.*

I have...

- [ ] confirmed the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title
- [ ] confirmed `!` in the type prefix if API or client breaking change
- [ ] confirmed all author checklist items have been addressed
- [ ] reviewed state machine logic
- [ ] reviewed API design and naming
- [ ] reviewed documentation is accurate
- [ ] reviewed tests and test coverage
- [ ] manually tested (if applicable)
---
 CHANGELOG.md  |  1 +
 types/coin.go | 13 ++++++++++++-
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1cbb65c163fe..a24cc57f3035 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -126,6 +126,7 @@ Ref: https://keepachangelog.com/en/1.0.0/
 * [\#9699](https://github.com/cosmos/cosmos-sdk/pull/9699) Add `:`, `.`, `-`, and `_` as allowed characters in the default denom regular expression.
 * (genesis) [\#9697](https://github.com/cosmos/cosmos-sdk/pull/9697) Ensure `InitGenesis` returns with non-empty validator set.
 * [\#10262](https://github.com/cosmos/cosmos-sdk/pull/10262) Remove unnecessary logging in `x/feegrant` simulation.
+* [\#10339](https://github.com/cosmos/cosmos-sdk/pull/10339) Improve performance of `removeZeroCoins` by only allocating memory when necessary
 * [\#10341](https://github.com/cosmos/cosmos-sdk/pull/10341) Move from `io/ioutil` to `io` and `os` packages.
 
 ### Bug Fixes
diff --git a/types/coin.go b/types/coin.go
index ea8557a5df57..ce222e1709f8 100644
--- a/types/coin.go
+++ b/types/coin.go
@@ -626,7 +626,18 @@ func (coins Coins) negative() Coins {
 
 // removeZeroCoins removes all zero coins from the given coin set in-place.
 func removeZeroCoins(coins Coins) Coins {
-	result := make([]Coin, 0, len(coins))
+	for i := 0; i < len(coins); i++ {
+		if coins[i].IsZero() {
+			break
+		} else if i == len(coins)-1 {
+			return coins
+		}
+	}
+
+	var result []Coin
+	if len(coins) > 0 {
+		result = make([]Coin, 0, len(coins)-1)
+	}
 
 	for _, coin := range coins {
 		if !coin.IsZero() {