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layout: Rewrite the block formatting context/float inline-size

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speculation code.

The old code tried to do the speculation as a single bottom-up pass
after intrinsic inline-size calculation, which was unable to handle
cases like this:

    <div>
        <div style="float: left">Foo</div>
    </div>
    <div>
        <div style="overflow: hidden">Bar</div>
    </div>

No single bottom-up pass could possibly handle this case, because the
inline-size of the float flowing out of the "Foo" block could never make
it down to the "Bar" block, where it is needed for speculation.

On the pages I tried, this regresses layout performance by 1%-2%.

I first noticed this breaking some pages, like the Google SERPs, several
months ago.
This commit is contained in:
Patrick Walton 2016-03-18 15:23:08 -07:00
parent 9b2ae3a62f
commit b29719e36b
15 changed files with 346 additions and 184 deletions
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6
components/layout/layout_thread.rs
View file

@ -1345,6 +1345,12 @@ impl LayoutThread {
self.time_profiler_chan.clone(),
|| sequential::resolve_generated_content(&mut root_flow, &layout_context));
// Guess float placement.
profile(time::ProfilerCategory::LayoutFloatPlacementSpeculation,
self.profiler_metadata(),
self.time_profiler_chan.clone(),
|| sequential::guess_float_placement(flow_ref::deref_mut(&mut root_flow)));
// Perform the primary layout passes over the flow tree to compute the locations of all
// the boxes.
if flow::base(&*root_flow).restyle_damage.intersects(REFLOW | REFLOW_OUT_OF_FLOW) {