Noticeable change in gas estimation when using `forge test --gas-report`

Component

Forge

Have you ensured that all of these are up to date?

[X] Foundry
[X] Foundryup

What version of Foundry are you on?

forge 0.2.0 (68c3663 2024-01-11T00:37:40.946762000Z)

What command(s) is the bug in?

forge test --gas-report

Operating System

Linux

Describe the bug

After Monday's release (d46bcb3ddc768b35da8d1d29f85886476f974128), I noticed that our Solidity benchmarks in CI got noticeably worse on a PR that shouldn't have a large impact on gas costs. After noticing this and being puzzled, I opened another PR with similarly minimal changes, and the benchmark had changes on the same order of magnitude. The benchmark below shows the difference (left is the newer commit using the new version of foundry and right is the old benchmark using the old version of foundry):

Hyperdrive Gas Benchmark

Benchmark suite	Current: 04cb6ca547fac568122625ee05c5189245314e37	Previous: aadaa9950e44c58da81ccfaacc5f71e7158dd286	Deviation	Status
`addLiquidity: min`	`1600` gas	`1600` gas	`0%`	🟰
`addLiquidity: avg`	`66750` gas	`55098` gas	`21.1478%`	🚨
`addLiquidity: max`	`275046` gas	`232446` gas	`18.3268%`	🚨
`checkpoint: min`	`1172` gas	`1172` gas	`0%`	🟰
`checkpoint: avg`	`48038` gas	`47937` gas	`0.2107%`	🚨
`checkpoint: max`	`202123` gas	`202123` gas	`0%`	🟰
`closeLong: min`	`1580` gas	`1580` gas	`0%`	🟰
`closeLong: avg`	`27900` gas	`26510` gas	`5.2433%`	🚨
`closeLong: max`	`147816` gas	`139624` gas	`5.8672%`	🚨
`closeShort: min`	`1549` gas	`1549` gas	`0%`	🟰
`closeShort: avg`	`29995` gas	`28777` gas	`4.2325%`	🚨
`closeShort: max`	`147189` gas	`144389` gas	`1.9392%`	🚨
`initialize: min`	`1538` gas	`1538` gas	`0%`	🟰
`initialize: avg`	`214974` gas	`181786` gas	`18.2566%`	🚨
`initialize: max`	`256760` gas	`256760` gas	`0%`	🟰
`openLong: min`	`1509` gas	`1509` gas	`0%`	🟰
`openLong: avg`	`50165` gas	`40502` gas	`23.8581%`	🚨
`openLong: max`	`185904` gas	`162207` gas	`14.6091%`	🚨
`openShort: min`	`1519` gas	`1519` gas	`0%`	🟰
`openShort: avg`	`47392` gas	`47335` gas	`0.1204%`	🚨
`openShort: max`	`161536` gas	`161536` gas	`0%`	🟰
`redeemWithdrawalShares: min`	`1575` gas	`1575` gas	`0%`	🟰
`redeemWithdrawalShares: avg`	`23340` gas	`18465` gas	`26.4013%`	🚨
`redeemWithdrawalShares: max`	`105958` gas	`84767` gas	`24.9991%`	🚨
`removeLiquidity: min`	`1661` gas	`1661` gas	`0%`	🟰
`removeLiquidity: avg`	`148623` gas	`118880` gas	`25.0193%`	🚨
`removeLiquidity: max`	`323560` gas	`258848` gas	`25%`	🚨

foundry-rs / foundry