8000 `es/minifier`: truncate literal in bitwise and · Issue #10390 · swc-project/swc · GitHub
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es/minifier: truncate literal in bitwise and #10390

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Le0Developer opened this issue Apr 19, 2025 · 1 comment
Open

es/minifier: truncate literal in bitwise and #10390

Le0Developer opened this issue Apr 19, 2025 · 1 comment
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@Le0Developer
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Describe the feature

I recently I encountered a & 0xfffffffc in my codebase (blanks out the lower 2 bits to align to a 4 byte boundary in base64 decoding).

This could be a & -4 instead.

This applies to all bitwise operations but I haven't encountered others with such high values so far.

Although there's some cases where staying positive is actually shorter (eg a & 0x80000000 is shorter than a & -0x80000000 which would be the correct "in bounds" literal)

Babel plugin or link to the feature description

https://play.swc.rs/?version=1.11.21&code=H4sIAAAAAAAAA0vOzyvOz0nVy8lP10hUUFMwqEiDgGRNACgym%2BMbAAAA&config=H4sIAAAAAAAAA42VS47bMAxA9z1F4HUX7aJFMQeYXc8gKBblaCqLhkh5Ygxy99K%2FxJ3QRjdBzMeP%2BJM%2BvpxO1RvV1cvpQ%2F7KR2czQb5%2Fi4SGxPYqkoqHDqjOoeNqgrevsw3b3ACPGkA%2FqkUYEQlE5m0kWGRtSMEPW%2Bc1tl0Goo1MpOKvtJCY%2FrVfWMb3EXAuW%2FkZMYJNB8RYMiExNJA1xzXGaDsC09useBlPanMg1EKMsDA402XsVJ5c4IBJYj5TB9aZGh0oKGSoOfSgmUksMUsk6Sn5TNjBuTTN1NBP1tDbWCwrMeE6tUROq3i9YCA2viSthDPcqcEMl%2BJ%2BtgzeZOCS07PdG4a005M%2FAFKBaImSbUHzO2l4mac9a39oGZKXkeVB4TLfWpYJGimqCcErlR0rA5mD1s0MrtQwVrbWjrPgnfJRcGDAe5kVxTW9B64vWtBxo9ErQPprvTZVMzD3Ldzh40Ic4FfJkvUBWzRay5d9SkN7xngQoAW%2BoDtQkFYw7uMst8S12%2BclOZDRAKeqFJrA8yUgC8Bo4nRZPs2GrId4NE3E8%2BOaWBRuq2bV2tRM%2B765Lxm7CD3EvTH%2BjxU5pHK2fpzqdbOfthd%2BaUNpZfHC928rWlN5vB3TT9WiK5uMpqGcH5Of1UNpfTruUapAv1fLuZa3v8TDE%2F3PBgAA

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@kdy1 kdy1 added this to the Planned milestone May 13, 2025
@Le0Developer
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Two more things i found:

  • the current optimization for a & 0xffffffff -> a | 0 does not apply for a & -1 which is identical.
  • bitshifts (a >> b) don't appear to qualify as "truncating to int". for example (a | 0) >>> 0 does not get reduced to a >>> 0 (same with (a | 0) >> 1)

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