| # Experimental |
| |
| This document describes some high-level experimental features that aim to enable more aggressive optimization. |
| |
| ## Enable access modification of kept items |
| |
| Access modification is important for optimization, but may be prohibited by broad keep rules. Currently keep rule authors must explicitly allow access modification using the `allowaccessmodification` modifier. |
| |
| It is possible to limit the negative impact of broad keep rules on optimization by changing keep rules to allow access modification by default. |
| |
| If the app is sensitive to whether a given class, field, or method is non-public or not, it should explicitly disallow access modification using the `disallowaccessmodification` modifier: |
| |
| ``` |
| -keep,disallowaccessmodification class com.example.** { <fields>; } |
| ``` |
| |
| Enable this feature: |
| |
| ``` |
| -Dcom.android.tools.r8.allowAccessModificationInKeepRule=1 |
| ``` |
| |
| ## Enable final modification of kept instance fields |
| |
| The ability to unset the final flag of fields is important for the ability to inline constructors that assign final fields. |
| |
| Final modification is currently tied to optimization, i.e., if a given rule prohibits optimization of a field (e.g., since the field is accessed using reflection) then the field's final flag cannot be modified by R8. |
| |
| It is possible to enable more constructor inlining by decoupling final modification from optimization and changing keep rules to allow final modification by default. |
| |
| If the app is sensitive to whether a given instance field is final or not, it should explicitly disallow final modification using the `disallowfinalmodification` modifier. |
| |
| ``` |
| -keep,disallowfinalmodification class com.example.** { <fields>; } |
| ``` |
| |
| Enable this feature: |
| |
| ``` |
| -Dcom.android.tools.r8.allowFinalModificationInKeepRule=1 |
| -Dcom.android.tools.r8.decoupleFinalModificationFromOptimization=1 |
| ``` |
| |
| ## Enable code analysis of kept methods |
| |
| When a method is kept, R8 will propagate any information about the behavior of the method to callers (e.g., the fact that the method always returns a non-null value). This is often overly conservative, since most kept methods will not have their implementation changed. |
| |
| It is possible to change this behavior so that keep rules authors explicitly need to state that a given method may have its implementation changed using the `allowcodereplacement` modifier. |
| |
| ``` |
| -keep,allowcodereplacement class com.example.** { <methods>; } |
| ``` |
| |
| Enable this feature: |
| |
| ``` |
| -Dcom.android.tools.r8.allowCodeReplacementInKeepRule=0 |
| -Dcom.android.tools.r8.decoupleCodeReplacementFromOptimization=1 |
| ``` |
