Andreas Kling 51758f3022 LibJS: Make bytecode register allocator O(1) ...

Generator::allocate_register used to scan the free pool to find the
lowest-numbered register and then Vec::remove it, making every
allocation O(n) in the size of the pool. When loading https://x.com/
on my Linux machine, we spent ~800ms in this function alone!

This logic only existed to match the C++ register allocation ordering
while transitioning from C++ to Rust in the LibJS compiler, so now
we can simply get rid of it and make it instant. :^)

So drop the "always hand out the lowest-numbered free register" policy
and use the pool as a plain LIFO stack. Pushing and popping the back
of the Vec are both O(1), and peak register usage is unchanged since
the policy only affects which specific register gets reused, not how
aggressively.

2026-04-21 13:59:55 +02:00

..

annex-b-function-in-if.txt

LibJS: Make bytecode register allocator O(1)

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annexb-function-existing-var.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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argument-postfix-self-move.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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argument-variables.txt

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arguments-with-arguments-fn.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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assign-to-argument-no-tdz.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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assign-to-let-variable-tdz.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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assign-to-parameter.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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async-await-in-try-catch.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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async-await.txt

LibJS: Make bytecode register allocator O(1)

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async-generator-yield-await.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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async-generator-yield.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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async-return-bare.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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baseline.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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bigint-binary-literal-fold.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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bigint-constant-folding.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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bigint-large-constant-folding.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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bigint-truthiness.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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bitwise-numeric-preconvert.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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block-function-declaration-order.txt

LibJS: Improve bytecode executable dump format

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block-scoped-function-no-tdz.txt

LibJS: Skip preserving zero-argument call callees

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block-scoping.txt

LibJS: Make bytecode register allocator O(1)

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call-spread-register-order.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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captured-variables.txt

LibJS: Skip preserving zero-argument call callees

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catch-scope-boundary.txt

LibJS: Make bytecode register allocator O(1)

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chained-member-call.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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class-computed-field-lhs-name.txt

LibJS: Make bytecode register allocator O(1)

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class-computed-key.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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class-environment.txt

LibJS: Make bytecode register allocator O(1)

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class-lhs-name-no-createvariable.txt

LibJS: Improve bytecode executable dump format

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class-literal-fields.txt

LibJS: Make bytecode register allocator O(1)

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computed-compound-assign-register-reuse.txt

LibJS: Make bytecode register allocator O(1)

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computed-member-access.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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computed-member-compound-assign.txt

LibJS: Make bytecode register allocator O(1)

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computed-string-object-literal.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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computed-string-to-ById.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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computed-update-register-order.txt

LibJS: Make bytecode register allocator O(1)

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condition-dead-code-elim.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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conditional-register-order.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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const-assignment-no-extra-tdz.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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const-fold-exponentiation.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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const-fold-template-literals.txt

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constant-fold-large-string-to-number.txt

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constant-fold-string-to-number.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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default-param-self-reference.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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delete-expression-register.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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delete-super-eval-order.txt

LibJS: Make bytecode register allocator O(1)

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delete-super-property.txt

LibJS: Make bytecode register allocator O(1)

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destructure-array-rest.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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destructuring-assignment-in-logical-and.txt

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destructuring-assignment.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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destructuring-let-compound-assign.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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destructuring-no-base-identifier.txt

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destructuring-param-no-param-expressions.txt

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do-while-register-allocation.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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double-constant-deduplication.txt

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eval-prevents-locals.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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eval-same-function.txt

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eval-scope-optimization.txt

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expression-identifier-number-format.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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for-in-block-order.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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for-in-lexical-scope.txt

LibJS: Cache stable for-in iteration at bytecode sites

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for-in-object-property-iterator-next.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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for-in-of-lhs-patterns.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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for-in-register-lifetime.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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for-in-var-function-lhs-name.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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for-loop-break-after-if-continue.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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for-loop-scoping.txt

LibJS: Make bytecode register allocator O(1)

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for-of-cond-rhs-block-order.txt

LibJS: Make bytecode register allocator O(1)

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for-of-continue-with-block-scope.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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for-of-iteration-env-capacity.txt

LibJS: Improve bytecode executable dump format

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for-of-iterator-close.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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for-of-rhs-precedence.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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for-try-finally-continue.txt

LibJS: Make bytecode register allocator O(1)

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generator-yield-call.txt

LibJS: Make bytecode register allocator O(1)

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generator-yield-finally.txt

LibJS: Make bytecode register allocator O(1)

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generator-yield-star.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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generator-yield.txt

LibJS: Make bytecode register allocator O(1)

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global-variables.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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if-else-register-lifetime.txt

LibJS: Make bytecode register allocator O(1)

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indexed-append-guards.txt

LibJS: Make bytecode register allocator O(1)

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invalid-lhs-assignment-no-dead-code.txt

LibJS: Skip preserving zero-argument call callees

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invalid-lhs-forin-no-dead-code.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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lexical-env-teardown.txt

LibJS: Make bytecode register allocator O(1)

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local-variables.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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logical-assignment-register-order.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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logical-constant-folding.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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logical-or-in-if-condition.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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logical-or-preferred-dst.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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mov-merging.txt

LibJS: Make bytecode register allocator O(1)

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named-class-expression-no-lhs-name-leak.txt

LibJS: Improve bytecode executable dump format

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named-function-expression.txt

LibJS: Improve bytecode executable dump format

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nested-for-loop-completion.txt

LibJS: Make bytecode register allocator O(1)

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nested-member-base-identifier.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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nested-try-finally-continue.txt

LibJS: Make bytecode register allocator O(1)

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numeric-class-field-name.txt

LibJS: Make bytecode register allocator O(1)

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numeric-getter-no-lhs-name.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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numeric-index-object-literal.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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numeric-property-key.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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object-rest-computed-key.txt

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optional-chain-base-identifier.txt

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optional-chain.txt

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parameter-createvariable-order.txt

LibJS: Skip preserving zero-argument call callees

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postfix-increment-private-member.txt

LibJS: Make bytecode register allocator O(1)

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postfix-update-in-logical-and.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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private-identifier-access-patterns.txt

LibJS: Improve bytecode executable dump format

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private-logical-assignment-register-order.txt

LibJS: Make bytecode register allocator O(1)

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private-method-call-description.txt

LibJS: Make bytecode register allocator O(1)

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regex-literals.txt

LibJS: Make bytecode register allocator O(1)

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resolve-this-caching.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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right-shift-by-zero.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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sequential-try-blocks.txt

LibJS: Make bytecode register allocator O(1)

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string-from-char-code-builtin.txt

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string-prototype-char-at-builtin.txt

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super-call-spread-register-order.txt

LibJS: Make bytecode register allocator O(1)

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super-computed-eval-order.txt

LibJS: Make bytecode register allocator O(1)

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super-computed-string-to-id.txt

LibJS: Make bytecode register allocator O(1)

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super-constructor-call.txt

LibJS: Make bytecode register allocator O(1)

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super-evaluation-order.txt

LibJS: Make bytecode register allocator O(1)

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super-for-of-resolve-order.txt

LibJS: Make bytecode register allocator O(1)

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super-length-access.txt

LibJS: Make bytecode register allocator O(1)

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super-method-call-order.txt

LibJS: Make bytecode register allocator O(1)

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super-optional-call-this.txt

LibJS: Make bytecode register allocator O(1)

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switch-completion-value.txt

LibJS: Make bytecode register allocator O(1)

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switch-local-only-let.txt

LibJS: Make bytecode register allocator O(1)

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switch-scoping.txt

LibJS: Make bytecode register allocator O(1)

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switch-with-block-scope-return.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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tagged-template-base-identifier.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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tagged-template-if-register-order.txt

LibJS: Make bytecode register allocator O(1)

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this-base-identifier.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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try-catch-completion-ordering.txt

LibJS: Improve bytecode executable dump format

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try-catch-finally-register.txt

LibJS: Improve bytecode executable dump format

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try-catch-scoping.txt

LibJS: Make bytecode register allocator O(1)

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try-catch-terminated.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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try-finally-continue.txt

LibJS: Make bytecode register allocator O(1)

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try-finally.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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update-member-expression.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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using-declaration-non-local-env.txt

LibJS: Improve bytecode executable dump format

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var-binding-access.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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var-env-capacity-with-param-expressions.txt

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var-hoisting-tdz.txt

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var-init-in-param-body-scope.txt

LibJS: Drop dead entry GetLexicalEnvironment loads

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var-shadow-in-default-param.txt

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with-return.txt

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with-statement.txt

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