RISC-V: Compute live ranges for pattern results
Improves RISC-V register pressure estimation by correctly tracking live ranges of pattern results during vectorization.
During vectorization on RISC-V, when a statement is replaced by a pattern statement, the live range calculation was incorrectly using the original variable. This change modifies the calculation to use the live range of the pattern result instead, leading to more accurate register pressure estimation and potentially better register allocation.
In Details
In the RISC-V backend, when vectorization replaces a statement with a pattern statement, costs::compute_local_live_ranges now correctly computes the live range of the pattern result instead of the original variable. This enhances register pressure estimation by accurately reflecting the lifetime of the pattern's output, particularly relevant for vectorization scenarios.
- RISC-V
- An open-standard instruction set architecture (ISA) based on Reduced Instruction Set Computing principles. GCC supports various RISC-V profiles.
- vectorization
- An optimization technique where a single instruction is used to operate on multiple data points simultaneously, often leveraging SIMD (Single Instruction, Multiple Data) instructions.
- live range
- In compiler theory, the live range of a variable is the section of the program where its value may be used. Accurate live range analysis is crucial for register allocation.
- register pressure
- A measure of how many registers are simultaneously needed by a program. High register pressure can lead to spills (storing values in memory) and reduced performance.
- pattern statement
- A statement that represents a specific computation or operation, often generated or recognized by the compiler during optimization passes like vectorization.