Ranger: Improve pointer range analysis for read-only aggregates
GCC's range analysis now provides better pointer ranges by removing special casing for pointers in read-only aggregates.
The GCC compiler’s range analysis pass has been improved to provide more accurate pointer ranges. By removing special casing for pointers within read-only aggregates, the analysis now treats pointers more consistently with integers. This change leads to better range information, especially for pointer types, and simplifies the internal code.
In Details
The gimple-range-fold.cc implementation of range_from_readonly_* functions no longer special-cases pointers. Instead, pointer ranges are accumulated similarly to integers. The boolean return value of range_from_readonly_load is re-purposed to signal the availability of a usable range. This change enhances precision for pointer analysis, including correctly handling zero-length arrays of pointers, which were previously incorrectly marked as non-null.
- range analysis
- A compiler optimization technique that determines the possible range of values a variable can take during program execution. This information is used to perform other optimizations.
- read-only aggregate
- A data structure (like an array or struct) that is treated as constant and cannot be modified after initialization. This includes elements like pointers within such structures.
- pointer
- A variable that stores the memory address of another variable. In C-like languages, pointers are fundamental for dynamic memory management and low-level data manipulation.
- GIMPLE
- GCC's internal three-address intermediate representation (IR) used after parsing and before optimization passes. It simplifies code for analysis and transformation.