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refactor(core): Use `~x` instead of `-x` which can result in `-0` (#39233) 

`expandoInstructions` uses negative numbers by `-x`. This has lead to
issues in the paste as `-0` is processed as float rather than integer
leading to de-optimization.

PR Close #39233
This commit is contained in:
Misko Hevery 2020-10-13 22:08:53 -07:00 committed by Alex Rickabaugh
parent 54303688fa
commit 2c31533f0a
1 changed files with 2 additions and 10 deletions
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12
packages/core/src/render3/instructions/shared.ts
View File

@ -79,12 +79,7 @@ export function setHostBindingsByExecutingExpandoInstructions(tView: TView, lVie
if (instruction <= 0) {
// Negative numbers mean that we are starting new EXPANDO block and need to update
// the current element and directive index.
// Important: In JS `-x` and `0-x` is not the same! If `x===0` then `-x` will produce
// `-0` which requires non standard math arithmetic and it can prevent VM optimizations.
// `0-0` will always produce `0` and will not cause a potential deoptimization in VM.
// TODO(misko): PERF This should be refactored to use `~instruction` as that does not
// suffer from `-0` and it is faster/more compact.
currentElementIndex = 0 - instruction;
currentElementIndex = ~instruction;
setSelectedIndex(currentElementIndex);
// Injector block and providers are taken into account.
@ -1373,10 +1368,7 @@ export function generateExpandoInstructionBlock(
tView.firstCreatePass, true,
'Expando block should only be generated on first create pass.');
// Important: In JS `-x` and `0-x` is not the same! If `x===0` then `-x` will produce `-0` which
// requires non standard math arithmetic and it can prevent VM optimizations.
// `0-0` will always produce `0` and will not cause a potential deoptimization in VM.
const elementIndex = 0 - tNode.index;
const elementIndex = ~tNode.index;
const providerStartIndex = tNode.providerIndexes & TNodeProviderIndexes.ProvidersStartIndexMask;
const providerCount = tView.data.length - providerStartIndex;
(tView.expandoInstructions || (tView.expandoInstructions = []))