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collapsing switch cases with same bodies, when not lined in a row #1070

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merged 8 commits into from Sep 19, 2021
Merged

collapsing switch cases with same bodies, when not lined in a row #1070

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22a892a
collapsing switch cases with same bodies, when not lined in a row
elad-yosifon Sep 15, 2021
1d39780
fix side-effects bug (collapse_same_branches_not_in_a_row_ensure_no_s…
elad-yosifon Sep 15, 2021
540c84f
fix fallthrough bug (collapse_same_branches_not_in_a_row_including_fa…
elad-yosifon Sep 15, 2021
508932b
PR changes
elad-yosifon Sep 17, 2021
896ea1c
collapse_same_branches_not_in_a_row_even_if_last_case_without_abort
elad-yosifon Sep 17, 2021
43fe7e7
PR changes + cleanups
elad-yosifon Sep 17, 2021
8ea4904
misc
elad-yosifon Sep 17, 2021
1985b9c
change empty branch to inert
elad-yosifon Sep 18, 2021
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47 changes: 43 additions & 4 deletions lib/compress/index.js
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Expand Up @@ -1598,6 +1598,49 @@ def_optimize(AST_Switch, function(self, compressor) {
while (i < len) eliminate_branch(self.body[i++], body[body.length - 1]);
self.body = body;

let default_or_exact = default_branch || exact_match;
default_branch = null;
exact_match = null;

// group equivalent branches so they will be located next to each other,
// that way the next micro-optimization will merge them.
// ** bail micro-optimization if not a simple switch case with breaks
if (body.every((branch, i) =>
(branch === default_or_exact || !branch.expression.has_side_effects(compressor))
&& (branch.body.length === 0 || aborts(branch) || body.length - 1 === i))
) {
for (let i = 0; i < body.length; i++) {
const branch = body[i];
for (let j = i + 1; j < body.length; j++) {
const next = body[j];
if (next.body.length === 0) continue;
const last_branch = j === (body.length - 1);
const equivalentBranch = branches_equivalent(next, branch, false);
if (equivalentBranch || (last_branch && branches_equivalent(next, branch, true))) {
if (!equivalentBranch && last_branch) {
next.body.push(make_node(AST_Break));
}

// let's find previous siblings with inert fallthrough...
let x = j - 1;
let fallthroughDepth = 0;
while (x > i) {
if (is_inert_body(body[x--])) {
fallthroughDepth++;
} else {
break;
}
}

const plucked = body.splice(j - fallthroughDepth, 1 + fallthroughDepth);
body.splice(i + 1, 0, ...plucked);
i += plucked.length;
}
}
}
}

// merge equivalent branches in a row
for (let i = 0; i < body.length; i++) {
let branch = body[i];
if (branch.body.length === 0) continue;
Expand All @@ -1618,10 +1661,6 @@ def_optimize(AST_Switch, function(self, compressor) {
}
}

let default_or_exact = default_branch || exact_match;
default_branch = null;
exact_match = null;

// Prune any empty branches at the end of the switch statement.
{
let i = body.length - 1;
Expand Down
288 changes: 288 additions & 0 deletions test/compress/switch.js
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Expand Up @@ -2447,6 +2447,294 @@ collapse_same_branches_2: {
expect_stdout: ["PASS", "PASS"]
}

collapse_same_branches_not_in_a_row: {
options = {
switches: true,
dead_code: true
}
input: {
switch (id(1)) {
case 1:
console.log("PASS")
break;
case 2:
console.log("FAIL");
break;
case 3:
console.log("PASS");
break;
}
}
expect: {
switch (id(1)) {
case 1:
case 3:
console.log("PASS");
break;
case 2:
console.log("FAIL");
}
}
expect_stdout: ["PASS"]
}

collapse_same_branches_not_in_a_row2: {
options = {
switches: true,
dead_code: true
}
input: {
switch (id(1)) {
case 1:
console.log("PASS");
break;
case 2:
console.log("FAIL");
break;
case 3:
console.log("PASS");
break;
case 4:
console.log("PASS");
break;
}
}
expect: {
switch (id(1)) {
case 1:
case 3:
case 4:
console.log("PASS");
break;
case 2:
console.log("FAIL");
}
}
expect_stdout: ["PASS"]
}

collapse_same_branches_not_in_a_row_including_fallthrough_with_same_body: {
options = {
switches: true,
dead_code: true
}
input: {
switch (id(1)) {
case 1:
console.log("PASS");
break;
case 2:
console.log("FAIL");
break;
case 3:
case 4:
console.log("PASS");
break;
case 9:
console.log("FAIL");
break;
case 5:
case 6:
case 7:
case 8:
console.log("PASS");
break;
}
}
expect: {
switch (id(1)) {
case 1:
case 3:
case 4:
case 5:
case 6:
case 7:
case 8:
console.log("PASS");
break;
case 2:
case 9:
console.log("FAIL");
}
}
expect_stdout: ["PASS"]
}

collapse_same_branches_not_in_a_row_ensure_no_side_effects: {
options = {
switches: true,
dead_code: true
}
input: {
let i = 1;
switch (id(2)) {
case 1:
console.log(1);
break;
case 2:
console.log(2);
break;
case ++i:
console.log(1);
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break;
}
}
expect: {
let i = 1;
switch (id(2)) {
case 1:
console.log(1);
break;
case 2:
console.log(2);
break;
case ++i:
console.log(1);
}
}
expect_stdout: ["2"]
}
collapse_same_branches_not_in_a_row_even_if_last_case_without_abort: {
options = {
switches: true,
dead_code: true
}
input: {
switch (id(3)) {
case 1:
console.log(1);
break;
case 2:
console.log(2);
break;
case 3:
console.log(1);
}
}
expect: {
switch (id(3)) {
case 1:
case 3:
console.log(1);
break;
case 2:
console.log(2);
}
}
expect_stdout: ["1"]
}


collapse_same_branches_as_default_not_in_a_row: {
options = {
switches: true,
dead_code: true
}
input: {
switch (id(1)) {
case 1:
console.log("PASS");
break;
case 2:
console.log("FAIL");
break;
case 3:
console.log("PREVENT_IFS");
break;
case 4:
console.log("PASS");
break;
default:
console.log("PASS");
break;
}
}
expect: {
switch (id(1)) {
default:
console.log("PASS");
break;
case 2:
console.log("FAIL");
break;
case 3:
console.log("PREVENT_IFS");
}
}
expect_stdout: ["PASS"]
}

collapse_same_branches_in_a_row2: {
options = {
switches: true,
dead_code: true
}
input: {
switch (id(1)) {
case 1:
console.log("PASS");
break;
case 2:
console.log("FAIL");
break;
case 3:
console.log("PASS");
break;
case 4:
console.log("FAIL");
break;
}
}
expect: {
switch (id(1)) {
case 1:
case 3:
console.log("PASS");
break;
case 2:
case 4:
console.log("FAIL");
}
}
expect_stdout: ["PASS"]
}

collapse_same_branches_in_a_row_with_return: {
options = {
switches: true,
dead_code: true
}
input: {
function fn() {
switch (id(1)) {
case 1:
return "PASS";
case 2:
return "FAIL";
case 3:
return "PASS";
case 4:
return "FAIL";
}
}
console.log(fn())
}
expect: {
function fn() {
switch (id(1)) {
case 1:
case 3:
return "PASS";
case 2:
case 4:
return "FAIL";
}
}
console.log(fn())
}
expect_stdout: ["PASS"]
}

// Empty branches at the end of the switch get trimmed
trim_empty_last_branches: {
options = {
Expand Down