compiler: simplify createObjectLayout #5145
Conversation
This simplifies the process of constructing and encoding layout bitmaps. Instead of creating big integers and merging them, we can create a pre-sized bitmap and set positions within it. This also changes the encoding logic to allow larger layouts to be encoded inline. We would previously not encode a layout inline unless the size was less than the width of the data field. This is overly conservative. A layout can be encoded inline as long as: 1. The size fits within the size field. 2. All set bits in the bitmap fit into the data field.
|
Are there any stdlib tests or hand-coded tests that exercise the new "larger layouts" logic? |
|
I added a test to ensure that it is encoded correctly. We do not currently have a meaningful way to test the scanning logic. |
|
Test corpus passes but I wouldn't mind having @aykevl take a second look. |
dgryski
left a comment
dgryski
left a comment
There was a problem hiding this comment.
Looks correct but I don't have enough experience in this area to be confident.
| // Create the global initializer. | ||
| bitmapBytes := make([]byte, int(objectSizeWords+7)/8) | ||
| bitmap.FillBytes(bitmapBytes) | ||
| reverseBytes(bitmapBytes) // big-endian to little-endian |
There was a problem hiding this comment.
This big/little endian conversion doesn't seem to have an equivalent in the new code.
There was a problem hiding this comment.
Correct. The old getPointerBitmap code used big.Int which is stored in big-endian so the reverseBytes code was needed to fix it. buildPointerBitmap writes the bitmap normally so no endian logic is necessary,
2 participants
This simplifies the process of constructing and encoding layout bitmaps. Instead of creating big integers and merging them, we can create a pre-sized bitmap and set positions within it.
This also changes the encoding logic to allow larger layouts to be encoded inline. We would previously not encode a layout inline unless the size was less than the width of the data field. This is overly conservative.
A layout can be encoded inline as long as: