WEDNESDAY, AUGUST 5, 2026
gcc
Check for undefined in operator_lshift::op1_range.
GCC's left shift range analysis now correctly handles undefined results.
The operator_lshift::op1_range function in GCC’s range-op.cc has been updated to correctly handle cases where the result of a left shift operation is undefined. If an undefined result is detected, the calculation is now aborted, preventing potential inaccuracies in value range analysis.
In Details
The operator_lshift::op1_range function in range-op.cc previously lacked explicit handling for undefined results when calculating the value range of a left shift. This commit introduces a check to detect such undefined outcomes and aborts the calculation if necessary. This ensures that the value range analysis remains sound and does not propagate incorrect or undefined range information.
For Context
- Value Range Analysis
- A compiler optimization technique that determines the possible range of values a variable or expression can take during program execution.
- Left Shift
- A bitwise operation that shifts the bits of a number to the left by a specified number of positions, effectively multiplying the number by powers of two.
- Undefined Behavior
- In programming, behavior that results from an invalid operation or incorrect use of a standard, for which the C++ standard imposes no requirements.