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refactor(minifier): move compress block to dce #6468

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Oct 12, 2024
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refactor(minifier): move compress block to dce #6468

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56 changes: 53 additions & 3 deletions crates/oxc_minifier/src/ast_passes/peephole_remove_dead_code.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -42,6 +42,10 @@ impl<'a> Traverse<'a> for PeepholeRemoveDeadCode {
}
}

fn exit_statement(&mut self, stmt: &mut Statement<'a>, ctx: &mut TraverseCtx<'a>) {
self.compress_block(stmt, ctx);
}

fn exit_statements(&mut self, stmts: &mut Vec<'a, Statement<'a>>, ctx: &mut TraverseCtx<'a>) {
if stmts.iter().any(|stmt| matches!(stmt, Statement::EmptyStatement(_))) {
stmts.retain(|stmt| !matches!(stmt, Statement::EmptyStatement(_)));
Expand Down Expand Up @@ -128,6 +132,27 @@ impl<'a> PeepholeRemoveDeadCode {
}
}

/// Remove block from single line blocks
/// `{ block } -> block`
fn compress_block(&mut self, stmt: &mut Statement<'a>, ctx: &mut TraverseCtx<'a>) {
if let Statement::BlockStatement(block) = stmt {
// Avoid compressing `if (x) { var x = 1 }` to `if (x) var x = 1` due to different
// semantics according to AnnexB, which lead to different semantics.
if block.body.len() == 1 && !block.body[0].is_declaration() {
*stmt = block.body.remove(0);
self.compress_block(stmt, ctx);
self.changed = true;
return;
}
if block.body.len() == 0
&& (ctx.parent().is_block_statement() || ctx.parent().is_program())
{
// Remove the block if it is empty and the parent is a block statement.
*stmt = ctx.ast.statement_empty(SPAN);
}
}
}

fn try_fold_if(
&mut self,
if_stmt: &mut IfStatement<'a>,
Expand Down Expand Up @@ -264,6 +289,34 @@ mod test {
test(js, expected);
}

#[test]
fn test_fold_block() {
fold("{{foo()}}", "foo()");
fold("{foo();{}}", "foo()");
fold("{{foo()}{}}", "foo()");
// fold("{{foo()}{bar()}}", "foo();bar()");
fold("{if(false)foo(); {bar()}}", "bar()");
fold("{if(false)if(false)if(false)foo(); {bar()}}", "bar()");

fold("{'hi'}", "");
// fold("{x==3}", "");
// fold("{`hello ${foo}`}", "");
// fold("{ (function(){x++}) }", "");
// fold_same("function f(){return;}");
// fold("function f(){return 3;}", "function f(){return 3}");
// fold_same("function f(){if(x)return; x=3; return; }");
// fold("{x=3;;;y=2;;;}", "x=3;y=2");

// Cases to test for empty block.
// fold("while(x()){x}", "while(x());");
// fold("while(x()){x()}", "while(x())x()");
// fold("for(x=0;x<100;x++){x}", "for(x=0;x<100;x++);");
// fold("for(x in y){x}", "for(x in y);");
// fold("for (x of y) {x}", "for(x of y);");
// fold_same("for (let x = 1; x <10; x++ ) {}");
// fold_same("for (var x = 1; x <10; x++ ) {}");
}

#[test]
#[ignore]
fn test_remove_no_op_labelled_statement() {
Expand Down Expand Up @@ -300,9 +353,6 @@ mod test {
fold("for(;false;) { foo(); continue }", "");

// fold("l1:for(;false;) { }", "");

// TODO handle single block statement
fold_same("for(;a;) { foo(); }");
}

#[test]
Expand Down
22 changes: 2 additions & 20 deletions crates/oxc_minifier/src/ast_passes/peephole_substitute_alternate_syntax.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -33,11 +33,6 @@ impl<'a> CompressorPass<'a> for PeepholeSubstituteAlternateSyntax {
}

impl<'a> Traverse<'a> for PeepholeSubstituteAlternateSyntax {
fn enter_statement(&mut self, stmt: &mut Statement<'a>, _ctx: &mut TraverseCtx<'a>) {
self.compress_block(stmt);
// self.compress_while(stmt);
}

fn exit_return_statement(
&mut self,
stmt: &mut ReturnStatement<'a>,
Expand Down Expand Up @@ -161,20 +156,6 @@ impl<'a> PeepholeSubstituteAlternateSyntax {

/* Statements */

/// Remove block from single line blocks
/// `{ block } -> block`
fn compress_block(&mut self, stmt: &mut Statement<'a>) {
if let Statement::BlockStatement(block) = stmt {
// Avoid compressing `if (x) { var x = 1 }` to `if (x) var x = 1` due to different
// semantics according to AnnexB, which lead to different semantics.
if block.body.len() == 1 && !block.body[0].is_declaration() {
*stmt = block.body.remove(0);
self.compress_block(stmt);
self.changed = true;
}
}
}

// /// Transforms `while(expr)` to `for(;expr;)`
// fn compress_while(&mut self, stmt: &mut Statement<'a>) {
// let Statement::WhileStatement(while_stmt) = stmt else { return };
Expand Down Expand Up @@ -531,7 +512,8 @@ mod test {
test("function f(){return void 0;}", "function f(){return}");
test("function f(){return void foo();}", "function f(){return void foo()}");
test("function f(){return undefined;}", "function f(){return}");
test("function f(){if(a()){return undefined;}}", "function f(){if(a())return}");
// Here we handle the block in dce.
test("function f(){if(a()){return undefined;}}", "function f(){if(a()){return}}");
}

#[test]
Expand Down
50 changes: 25 additions & 25 deletions crates/oxc_minifier/tests/ast_passes/dead_code_elimination.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -18,57 +18,57 @@ fn test_same(source_text: &str) {

#[test]
fn dce_if_statement() {
test("if (true) { foo }", "{ foo }");
test("if (true) { foo } else { bar }", "{ foo }");
test("if (false) { foo } else { bar }", "{ bar }");
test("if (true) { foo }", "foo");
test("if (true) { foo } else { bar }", "foo");
test("if (false) { foo } else { bar }", "bar");

test("if (xxx) { foo } else if (false) { bar }", "if (xxx) { foo }");
test("if (xxx) { foo } else if (false) { bar } else { baz }", "if (xxx) { foo } else { baz }");
test("if (xxx) { foo } else if (false) { bar } else if (false) { baz }", "if (xxx) { foo }");
test("if (xxx) { foo } else if (false) { bar }", "if (xxx) foo");
test("if (xxx) { foo } else if (false) { bar } else { baz }", "if (xxx) foo; else baz");
test("if (xxx) { foo } else if (false) { bar } else if (false) { baz }", "if (xxx) foo");
test(
"if (xxx) { foo } else if (false) { bar } else if (false) { baz } else { quaz }",
"if (xxx) { foo } else { quaz }",
"if (xxx) foo; else quaz",
);
test(
"if (xxx) { foo } else if (true) { bar } else if (false) { baz }",
"if (xxx) { foo } else { bar }",
"if (xxx) foo; else bar",
);
test(
"if (xxx) { foo } else if (false) { bar } else if (true) { baz }",
"if (xxx) { foo } else { baz }",
"if (xxx) foo; else baz",
);
test(
"if (xxx) { foo } else if (true) { bar } else if (true) { baz }",
"if (xxx) { foo } else { bar }",
"if (xxx) foo; else bar",
);
test(
"if (xxx) { foo } else if (false) { var a; var b; } else if (false) { var c; var d; }",
"if (xxx) { foo } else var c, d;",
"if (xxx) foo; else var c, d;",
);

test("if (!false) { foo }", "{ foo }");
test("if (!true) { foo } else { bar }", "{ bar }");
test("if (!false) { foo }", "foo");
test("if (!true) { foo } else { bar }", "bar");

test("if (!false && xxx) { foo }", "if (xxx) { foo; }");
test("if (!true && yyy) { foo } else { bar }", "{ bar }");
test("if (!false && xxx) { foo }", "if (xxx) foo");
test("if (!true && yyy) { foo } else { bar }", "bar");

test("if (true || xxx) { foo }", "{ foo }");
test("if (false || xxx) { foo }", "if (xxx) { foo }");
test("if (true || xxx) { foo }", "foo");
test("if (false || xxx) { foo }", "if (xxx) foo");

test("if ('production' == 'production') { foo } else { bar }", "{ foo }");
test("if ('development' == 'production') { foo } else { bar }", "{ bar }");
test("if ('production' == 'production') { foo } else { bar }", "foo");
test("if ('development' == 'production') { foo } else { bar }", "bar");

test("if ('production' === 'production') { foo } else { bar }", "{ foo }");
test("if ('development' === 'production') { foo } else { bar }", "{ bar }");
test("if ('production' === 'production') { foo } else { bar }", "foo");
test("if ('development' === 'production') { foo } else { bar }", "bar");

// Shadowed `undefined` as a variable should not be erased.
// This is a rollup test.
test_same("function foo(undefined) { if (!undefined) { } }");

test("function foo() { if (undefined) { bar } }", "function foo() { }");
test_same("function foo() { { bar } }");
test("function foo() { { bar } }", "function foo() { bar }");

test("if (true) { foo; } if (true) { foo; }", "{ foo; } { foo; }");
test("if (true) { foo; } if (true) { foo; }", "foo; foo;");

test(
"
Expand All @@ -83,11 +83,11 @@ fn dce_if_statement() {
// nested expression
test(
"const a = { fn: function() { if (true) { foo; } } }",
"const a = { fn: function() { { foo; } } }",
"const a = { fn: function() { foo; } }",
);

// parenthesized
test("if (!!(false)) { REMOVE; } else { KEEP; }", "{ KEEP }");
test("if (!!(false)) { REMOVE; } else { KEEP; }", "KEEP");

// typeof
test("if (typeof 1 !== 'number') { REMOVE; }", "");
Expand Down