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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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52 changes: 51 additions & 1 deletion lib/compress/index.js
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Expand Up @@ -145,7 +145,8 @@ import {

_INLINE,
_NOINLINE,
_PURE
_PURE,
AST_Case
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} from "../ast.js";
import {
defaults,
Expand Down Expand Up @@ -1598,6 +1599,52 @@ def_optimize(AST_Switch, function(self, compressor) {
while (i < len) eliminate_branch(self.body[i++], body[body.length - 1]);
self.body = body;

// 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 =>
(
branch instanceof AST_Default || // default
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!branch.expression.has_side_effects(compressor) // or no_side_effects
)
&& (
branch.body.length === 0 // empty
|| is_break(branch.body[branch.body.length - 1], compressor) // or has a break
|| is_return(branch.body[branch.body.length - 1]) // or has a return
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)
)) {
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for (let i = 0; i < body.length; i++) {
let branch = body[i];
if (branch.body.length === 0) continue;
if (!aborts(branch)) continue;
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for (let j = i + 1; j < body.length; j++) {
let next = body[j];
if (next.body.length === 0) continue;
if (
branches_equivalent(next, branch, false)
|| (j === body.length - 1 && branches_equivalent(next, branch, true))
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) {
// let's find previous siblings with empty fallthrough...
let x = j-1;
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let fallthroughDepth = 0;
while(x > i) {
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let previousSiblingBranch = body[x--];
if(previousSiblingBranch.body.length === 0 && previousSiblingBranch instanceof AST_Case) {
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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 Down Expand Up @@ -1887,6 +1934,9 @@ def_optimize(AST_Switch, function(self, compressor) {
return node instanceof AST_Break
&& stack.loopcontrol_target(node) === self;
}
function is_return(node) {
return node instanceof AST_Return;
}
function is_inert_body(branch) {
return !aborts(branch) && !make_node(AST_BlockStatement, branch, {
body: branch.body
Expand Down
258 changes: 258 additions & 0 deletions test/compress/switch.js
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Expand Up @@ -2447,6 +2447,264 @@ 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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}
}
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_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