x/bank setSupply is inefficient

[aaronc]

Summary of Bug

In #7092, we removed the global supply blog but setSupply, BurnCoins and MintCoins are still iterating over the whole supply and re-writing the whole supply store for every operation.

cosmos-sdk/x/bank/keeper/keeper.go

Lines 195 to 211 in 641b13e

	// update supply for coins which have non zero amount
	for _, coin := range storeSupply {
	if supply.AmountOf(coin.Denom).IsZero() {
	zeroCoin := &sdk.Coin{
	Denom: coin.Denom,
	Amount: sdk.NewInt(0),
	}
	bz := k.cdc.MustMarshalBinaryBare(zeroCoin)
	supplyStore.Set([]byte(coin.Denom), bz)
	}
	}
	newSupply = append(newSupply, supply...)
	for i := range newSupply {
	bz := k.cdc.MustMarshalBinaryBare(&supply[i])
	supplyStore.Set([]byte(supply[i].Denom), bz)
	}

cosmos-sdk/x/bank/keeper/keeper.go

Lines 407 to 410 in 641b13e

	supply := k.GetTotalSupply(ctx)
	supply = supply.Sub(amt)
	k.setSupply(ctx, supply)

Proposed Fix

Set the supply one denom at a time rather than reading and writing the whole supply for each operation. A related issue may be #4076 as the sdk.Coins array is inherently inefficient when there are multiple denoms.

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[aaronc]

I think this should go in v0.43 to complete #7092.

[aaronc]

I can open a small PR if it's helpful.

[jgimeno]

Remember that when we set some supply which is zero, in the past as we rewrote the full struct we did not have this problem, but as soon as the value is zero it needs to rewrite the zero value.

[jgimeno]

@aaronc if it is ok I am gonna take this one

[aaronc]

@aaronc if it is ok I am gonna take this one

go for it!