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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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10
components/layout/traversal.rs
View file

@ -7,8 +7,8 @@
use construct::FlowConstructor;
use context::{LayoutContext, SharedLayoutContext};
use display_list_builder::DisplayListBuildState;
use flow::{PostorderFlowTraversal, PreorderFlowTraversal};
use flow::{self, Flow, CAN_BE_FRAGMENTED};
use flow::{CAN_BE_FRAGMENTED, Flow, ImmutableFlowUtils, PostorderFlowTraversal};
use flow::{PreorderFlowTraversal, self};
use gfx::display_list::OpaqueNode;
use incremental::{BUBBLE_ISIZES, REFLOW, REFLOW_OUT_OF_FLOW, REPAINT, RestyleDamage};
use std::mem;
@ -179,10 +179,12 @@ pub struct AssignBSizes<'a> {
impl<'a> PostorderFlowTraversal for AssignBSizes<'a> {
#[inline]
fn process(&self, flow: &mut Flow) {
// Can't do anything with flows impacted by floats until we reach their inorder parent.
// Can't do anything with anything that floats might flow through until we reach their
// inorder parent.
//
// NB: We must return without resetting the restyle bits for these, as we haven't actually
// reflowed anything!
if flow::base(flow).flags.impacted_by_floats() {
if flow.floats_might_flow_through() {
return
}