compiler: do not perform nil checking when indexing slices #968
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
The x/tools/go/ssa package splits slice loads/stores into two
operations. So for code like this:
x = p[3]
It has two instructions:
x_ptr = &p[3]
x = *x_ptr
This makes the IR simpler, but also means we're accidentally inserting
more nil checks than necessary: the slice index operation has
effectively already checked for nil by performing a bounds check.
Therefore, omit nil pointer checks for pointers created by
*ssa.IndexAddr.
This change is necessary to make sure a future removal of runtime.isnil
will not cause the escape analysis pass to regress. Apart from that, it
reduces code size slightly in many smoke tests (with no increases in
code size).
Member
|
@aykevl this PR now needs a merge conflict resolved. Thanks. |
Member
Author
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
The x/tools/go/ssa package splits slice loads/stores into two operations. So for code like this:
It outputs two instructions:
This makes the IR simpler, but also means we're accidentally inserting more nil checks than necessary: the slice index operation has effectively already checked for nil by performing a bounds check. Therefore, omit nil pointer checks for pointers created by
*ssa.IndexAddr.This change is necessary to make sure a future removal of
runtime.isnilwill not cause the escape analysis pass to regress. Apart from that, it reduces code size slightly in many smoke tests (with no increases in code size).