New submission from Serhiy Storchaka:
For now multiple set functions call helpers that returns one of three possible
values (0, 1, and -1 for error) and then analyze return code in the loop.
while (...) {
rv = some_set_operation();
if (rv < 0) {
// clean up
return NULL;
}
if (rv) {
other_set_operation();
}
// if (rv == 0) do nothing
}
If rv is 0 or 1, it is tested two times. If rv is -1 (unlikely), it is tested
only once.
It is possible to rewrite testing in other way:
while (...) {
rv = some_set_operation();
if (rv != 0) { // 1 or -1
if (rv < 0) {
// clean up
return NULL;
}
other_set_operation();
}
}
Now if rv is 0 (common case), it is tested only once, and likely the test jump
will be merged with unconditional loop jump.
I have no benchmarking results, but I suppose that such rewritting will
generate better machine code.
----------
components: Interpreter Core
files: set_branch_optimizations.patch
keywords: patch
messages: 246395
nosy: rhettinger, serhiy.storchaka
priority: normal
severity: normal
stage: patch review
status: open
title: Minor branch optimization in set implementation
type: enhancement
versions: Python 3.6
Added file: http://bugs.python.org/file39878/set_branch_optimizations.patch
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