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improve collapse_vars on AST_Var (#1828)

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Perform the same cascaded scanning within `var` statement as we do on array of statements.
This commit is contained in:
Alex Lam S.L
2017-04-19 04:49:09 +08:00
committed by GitHub
parent b4b9305db0
commit 4dcff038cb
2 changed files with 123 additions and 95 deletions
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49
lib/compress.js
View File

@@ -644,21 +644,21 @@ merge(Compressor.prototype, {
var scope = compressor.find_parent(AST_Scope);
var toplevel = compressor.option("toplevel");
for (var stat_index = statements.length; --stat_index >= 0;) {
var stat = statements[stat_index];
var var_names_seen = Object.create(null);
var side_effects_encountered = false;
var lvalues_encountered = false;
var lvalues = Object.create(null);
var prev_stat_index, var_defs, var_defs_index;
var stat_index;
var prev_stat_index;
var def_stat_index;
var stat;
var var_defs;
var var_defs_index;
for (stat_index = statements.length; --stat_index >= 0;) {
stat = statements[stat_index];
// Scan variable definitions from right to left.
if (stat instanceof AST_Definitions) {
prev_stat_index = stat_index;
var_defs = stat.definitions;
for (var_defs_index = var_defs.length - 1; --var_defs_index >= 0;) {
if (collapse(var_defs[var_defs_index + 1])) break;
for (def_stat_index = var_defs.length; --def_stat_index >= 1;) {
stat = var_defs[def_stat_index];
scan_var_defs(def_stat_index);
}
} else if (stat_index > 0) {
// The variable definition must precede a statement.
@@ -666,48 +666,51 @@ merge(Compressor.prototype, {
var prev_stat = statements[prev_stat_index];
if (!(prev_stat instanceof AST_Definitions)) continue;
var_defs = prev_stat.definitions;
for (var_defs_index = var_defs.length; --var_defs_index >= 0;) {
if (collapse(stat)) break;
}
scan_var_defs(var_defs.length);
}
}
return statements;
function collapse(stat) {
function scan_var_defs(end_pos) {
var var_names_seen = Object.create(null);
var side_effects_encountered = false;
var lvalues_encountered = false;
var lvalues = Object.create(null);
for (var_defs_index = end_pos; --var_defs_index >= 0;) {
var var_decl = var_defs[var_defs_index];
// `drop_unused()` shuffles variables without values to the top,
// so we can terminate upon first sighting as an optimization.
if (var_decl.value == null) return true;
if (var_decl.value == null) break;
var var_name = var_decl.name.name;
// Bail if we've seen a var definition of same name before.
if (var_name in var_names_seen) return true;
if (var_name in var_names_seen) break;
var_names_seen[var_name] = true;
// Only interested in non-constant values.
if (var_decl.value.is_constant()) return;
if (var_decl.value.is_constant()) continue;
// Only interested in cases with just one reference to the variable.
var def = var_decl.name.definition();
if (def.references.length !== 1
|| var_name == "arguments" || (!toplevel && def.global)) {
side_effects_encountered = true;
return;
continue;
}
var ref = def.references[0];
// Don't replace ref if eval() or with statement in scope.
if (ref.scope.uses_eval || ref.scope.uses_with) return true;
if (ref.scope.uses_eval || ref.scope.uses_with) break;
// Restrict var replacement to constants if side effects encountered.
if (side_effects_encountered |= lvalues_encountered) return;
if (side_effects_encountered |= lvalues_encountered) continue;
var value_has_side_effects = var_decl.value.has_side_effects(compressor);
// Non-constant single use vars can only be replaced in same scope.
if (ref.scope !== scope) {
side_effects_encountered |= value_has_side_effects;
return;
continue;
}
// Detect lvalues in var value.
@@ -764,6 +767,7 @@ merge(Compressor.prototype, {
);
stat.transform(tt);
}
}
function is_lvalue(node, parent) {
return node instanceof AST_SymbolRef && is_lhs(node, parent);
@@ -777,6 +781,7 @@ merge(Compressor.prototype, {
var_decl.value = null;
var_defs.splice(var_defs_index, 1);
def_stat_index--;
if (var_defs.length === 0) {
statements.splice(prev_stat_index, 1);
stat_index--;

23
test/compress/collapse_vars.js
View File

@@ -1654,3 +1654,26 @@ iife_2: {
}(bar());
}
}
var_defs: {
options = {
collapse_vars:true, sequences:true, properties:true, dead_code:true, conditionals:true,
comparisons:true, evaluate:true, booleans:true, loops:true, unused:true, hoist_funs:true,
keep_fargs:true, if_return:true, join_vars:true, cascade:true, side_effects:true
}
input: {
var f1 = function(x, y) {
var a, b, r = x + y, q = r * r, z = q - r, a = z, b = 7;
console.log(a + b);
};
f1("1", 0);
}
expect: {
var f1 = function(x, y) {
var r = x + y, a = r * r - r, b = 7;
console.log(a + b);
};
f1("1", 0);
}
expect_stdout: "97"
}