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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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26
components/layout/sequential.rs
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@ -8,17 +8,18 @@ use app_units::Au;
use context::{LayoutContext, SharedLayoutContext};
use display_list_builder::DisplayListBuildState;
use euclid::point::Point2D;
use floats::SpeculatedFloatPlacement;
use flow::{PostorderFlowTraversal, PreorderFlowTraversal};
use flow::{self, Flow, ImmutableFlowUtils, InorderFlowTraversal, MutableFlowUtils};
use flow_ref::{self, FlowRef};
use fragment::FragmentBorderBoxIterator;
use generated_content::ResolveGeneratedContent;
use gfx::display_list::{DisplayListEntry, StackingContext};
use incremental::STORE_OVERFLOW;
use incremental::{REFLOW, STORE_OVERFLOW};
use style::dom::TNode;
use style::traversal::DomTraversalContext;
use traversal::{AssignBSizes, AssignISizes};
use traversal::{BubbleISizes, BuildDisplayList, ComputeAbsolutePositions, PostorderNodeMutTraversal};
use traversal::{AssignBSizes, AssignISizes, BubbleISizes, BuildDisplayList};
use traversal::{ComputeAbsolutePositions, PostorderNodeMutTraversal};
use util::opts;
pub use style::sequential::traverse_dom;
@ -133,3 +134,22 @@ pub fn store_overflow(layout_context: &LayoutContext, flow: &mut Flow) {
flow::mut_base(flow).restyle_damage.remove(STORE_OVERFLOW);
}
/// Guesses how much inline size will be taken up by floats on the left and right sides of the
/// given flow. This is needed to speculatively calculate the inline sizes of block formatting
/// contexts. The speculation typically succeeds, but if it doesn't we have to lay it out again.
pub fn guess_float_placement(flow: &mut Flow) {
if !flow::base(flow).restyle_damage.intersects(REFLOW) {
return
}
let mut floats_in = SpeculatedFloatPlacement::compute_floats_in_for_first_child(flow);
for kid in flow::mut_base(flow).child_iter() {
floats_in.compute_floats_in(kid);
flow::mut_base(kid).speculated_float_placement_in = floats_in;
guess_float_placement(kid);
floats_in = flow::base(kid).speculated_float_placement_out;
}
floats_in.compute_floats_out(flow);
flow::mut_base(flow).speculated_float_placement_out = floats_in
}