[ConstantInt] Disable implicit truncation in ConstantInt::get() #171456
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nikic
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Explicitly cast the value to (int) before negating, so it gets properly sign extended. Otherwise we end up with a large unsigned value instead of a negative value for large bit widths. This was found while working on #171456.
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Explicitly cast the value to (int) before negating, so it gets properly sign extended. Otherwise we end up with a large unsigned value instead of a negative value for large bit widths. This was found while working on llvm/llvm-project#171456.
anonymouspc
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Explicitly cast the value to (int) before negating, so it gets properly sign extended. Otherwise we end up with a large unsigned value instead of a negative value for large bit widths. This was found while working on llvm#171456.
nikic
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Dec 16, 2025
Use getSigned() to create the 1 or -1 constant, so it gets properly sign extended. This miscompile was found while working on #171456.
To limit scope.
To reduce scope.
For now, we should implicitly truncate overflowing allocation sizes when expanding GEPs, like we do in other places.
This value may be -1.
It's okay if the pattern value gets truncated here, it's a splat.
For non-fragile this is a negative value.
This may be -1 for incompete array types.
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…172301) Use getSigned() to create the 1 or -1 constant, so it gets properly sign extended. This miscompile was found while working on llvm/llvm-project#171456.
🐧 Linux x64 Test Results
✅ The build succeeded and all tests passed. |
The value is always stored as an unsigned number, even if the char type is signed, so we have to allow truncation here.
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Disable implicit truncation in the ConstantInt constructor by default. This means that it needs to be passed a signed/unsigned (depending on the IsSigned flag) value matching the bit width.
The intention is to prevent the recurring bug where people write something like
ConstantInt::get(Ty, -1), and this "works" untilTyis larger than 64-bit and then the value is incorrect due to missing type extension.This is the continuation of #112670, which originally allowed implicit truncation in this constructor to reduce initial scope of the change.
This PR is WIP. Most parts will be landed separately.