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Skip simple conditional flows in control flow graph

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This commit is contained in:
Anders Hejlsberg
2016-05-04 15:17:39 -07:00
parent e49773a7e9
commit 9fa5971af0
1 changed files with 18 additions and 1 deletions
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19
src/compiler/binder.ts
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@@ -695,6 +695,23 @@ namespace ts {
};
}
function skipSimpleConditionalFlow(flow: FlowNode) {
// We skip over simple conditional flows of the form 'x ? aaa : bbb', where 'aaa' and 'bbb' contain
// no constructs that affect control flow type analysis. Such simple flows have no effect on the
// code paths that follow and ignoring them means we'll do less work.
if (flow.flags & FlowFlags.BranchLabel && (<FlowLabel>flow).antecedents.length === 2) {
const a = (<FlowLabel>flow).antecedents[0];
const b = (<FlowLabel>flow).antecedents[1];
if ((a.flags & FlowFlags.TrueCondition && b.flags & FlowFlags.FalseCondition ||
a.flags & FlowFlags.FalseCondition && b.flags & FlowFlags.TrueCondition) &&
(<FlowCondition>a).antecedent === (<FlowCondition>b).antecedent &&
(<FlowCondition>a).expression === (<FlowCondition>b).expression) {
return (<FlowCondition>a).antecedent;
}
}
return flow;
}
function finishFlowLabel(flow: FlowLabel): FlowNode {
const antecedents = flow.antecedents;
if (!antecedents) {
@@ -703,7 +720,7 @@ namespace ts {
if (antecedents.length === 1) {
return antecedents[0];
}
return flow;
return skipSimpleConditionalFlow(flow);
}
function isStatementCondition(node: Node) {