[css-flexbox] Performance optimization: Only apply min-width: auto when flex-shrinking an item

Source/core/layout/LayoutFlexibleBox.cpp

 /*
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 816 matching lines @@
         if (isHorizontalFlow()) {
             child->setMarginLeft(computeChildMarginValue(child->style()->marginLeft()));
             child->setMarginRight(computeChildMarginValue(child->style()->marginRight()));
         } else {
             child->setMarginTop(computeChildMarginValue(child->style()->marginTop()));
             child->setMarginBottom(computeChildMarginValue(child->style()->marginBottom()));
         }
     }
 }
 
-LayoutUnit LayoutFlexibleBox::adjustChildSizeForMinAndMax(LayoutBox& child, LayoutUnit childSize)
+LayoutUnit LayoutFlexibleBox::adjustChildSizeForMinAndMax(LayoutBox& child, LayoutUnit childSize, bool childShrunk)
 {
     Length max = isHorizontalFlow() ? child.style()->maxWidth() : child.style()->maxHeight();
     LayoutUnit maxExtent = -1;
     if (max.isSpecifiedOrIntrinsic()) {
         maxExtent = computeMainAxisExtentForChild(child, MaxSize, max);
         if (maxExtent != -1 && childSize > maxExtent)
             childSize = maxExtent;
     }
 
     Length min = isHorizontalFlow() ? child.style()->minWidth() : child.style()->minHeight();
     LayoutUnit minExtent = 0;
     if (min.isSpecifiedOrIntrinsic()) {
         minExtent = computeMainAxisExtentForChild(child, MinSize, min);
         // computeMainAxisExtentForChild can return -1 when the child has a percentage
         // min size, but we have an indefinite size in that axis.
         minExtent = std::max(LayoutUnit(), minExtent);
-    } else if (min.isAuto() && mainAxisOverflowForChild(child) == OVISIBLE) {
+    } else if (childShrunk && min.isAuto() && mainAxisOverflowForChild(child) == OVISIBLE) {
         // css-flexbox section 4.5
         LayoutUnit contentSize = computeMainAxisExtentForChild(child, MinSize, Length(MinContent));
         ASSERT(contentSize >= 0);
         if (maxExtent != -1 && contentSize > maxExtent)
             contentSize = maxExtent;
 
         bool hasClampedSize = !childPreferredMainAxisContentExtentRequiresLayout(child);
         if (hasClampedSize) {
             const Length& flexBasis = flexBasisForChild(child);
             bool flexBasisIsDefinite = flexBasis.isFixed() || (flexBasis.isPercent() && mainAxisExtentIsDefinite());
@@ skipping 33 matching lines @@
         if (child->isOutOfFlowPositioned()) {
             orderedChildren.append(child);
             continue;
         }
 
         LayoutUnit childMainAxisExtent = preferredMainAxisContentExtentForChild(*child, relayoutChildren);
         LayoutUnit childMainAxisMarginBorderPadding = mainAxisBorderAndPaddingExtentForChild(*child)
             + (isHorizontalFlow() ? child->marginWidth() : child->marginHeight());
         LayoutUnit childFlexBaseSize = childMainAxisExtent + childMainAxisMarginBorderPadding;
 
-        LayoutUnit childMinMaxAppliedMainAxisExtent = adjustChildSizeForMinAndMax(*child, childMainAxisExtent);
+        LayoutUnit childMinMaxAppliedMainAxisExtent = adjustChildSizeForMinAndMax(*child, childMainAxisExtent, false);

[leviw_travelin_and_unemployed, 2015/04/17 19:17:40]

Maybe make the parameter default to false to avoid this nasty "false".

[cbiesinger, 2015/04/17 19:39:25]

Done.

         LayoutUnit childHypotheticalMainSize = childMinMaxAppliedMainAxisExtent + childMainAxisMarginBorderPadding;
 
         if (isMultiline() && sumHypotheticalMainSize + childHypotheticalMainSize > lineBreakLength && lineHasInFlowItem)
             break;
         orderedChildren.append(child);
         lineHasInFlowItem  = true;
         sumFlexBaseSize += childFlexBaseSize;
         totalFlexGrow += child->style()->flexGrow();
         totalWeightedFlexShrink += child->style()->flexShrink() * childMainAxisExtent;
         sumHypotheticalMainSize += childHypotheticalMainSize;
@@ skipping 28 matching lines @@
             childSizes.append(0);
             continue;
         }
 
         if (inflexibleItems.contains(child)) {
             childSizes.append(inflexibleItems.get(child));
         } else {
             LayoutUnit preferredChildSize = preferredMainAxisContentExtentForChild(*child);
             LayoutUnit childSize = preferredChildSize;
             double extraSpace = 0;
-            if (availableFreeSpace > 0 && totalFlexGrow > 0 && flexSign == PositiveFlexibility && std::isfinite(totalFlexGrow))
+            bool childShrunk = false;
+            if (availableFreeSpace > 0 && totalFlexGrow > 0 && flexSign == PositiveFlexibility && std::isfinite(totalFlexGrow)) {
                 extraSpace = availableFreeSpace * child->style()->flexGrow() / totalFlexGrow;
-            else if (availableFreeSpace < 0 && totalWeightedFlexShrink > 0 && flexSign == NegativeFlexibility && std::isfinite(totalWeightedFlexShrink))
+            } else if (availableFreeSpace < 0 && totalWeightedFlexShrink > 0 && flexSign == NegativeFlexibility && std::isfinite(totalWeightedFlexShrink) && child->style()->flexShrink()) {
                 extraSpace = availableFreeSpace * child->style()->flexShrink() * preferredChildSize / totalWeightedFlexShrink;
+                childShrunk = true;
+            }
             if (std::isfinite(extraSpace))
                 childSize += LayoutUnit::fromFloatRound(extraSpace);
 
-            LayoutUnit adjustedChildSize = adjustChildSizeForMinAndMax(*child, childSize);
+            LayoutUnit adjustedChildSize = adjustChildSizeForMinAndMax(*child, childSize, childShrunk);
             ASSERT(adjustedChildSize >= 0);
             childSizes.append(adjustedChildSize);
             usedFreeSpace += adjustedChildSize - preferredChildSize;
 
             LayoutUnit violation = adjustedChildSize - childSize;
             if (violation > 0)
                 minViolations.append(Violation(child, adjustedChildSize));
             else if (violation < 0)
                 maxViolations.append(Violation(child, adjustedChildSize));
             totalViolation += violation;
@@ skipping 464 matching lines @@
             ASSERT(child);
             LayoutUnit lineCrossAxisExtent = lineContexts[lineNumber].crossAxisExtent;
             LayoutUnit originalOffset = lineContexts[lineNumber].crossAxisOffset - crossAxisStartEdge;
             LayoutUnit newOffset = contentExtent - originalOffset - lineCrossAxisExtent;
             adjustAlignmentForChild(*child, newOffset - originalOffset);
         }
     }
 }
 
 }