LoongArch: Avoid relocation for addsy/subsy within the same fragment
Optimizes LoongArch assembler by skipping relocations when addsy and subsy fall within the same fragment, reducing object file size.
This commit enhances the LoongArch assembler’s efficiency by preventing unnecessary relocations when addsy and subsy directives appear within the same code fragment. It refines the handling of linker-relaxable instructions and alignment no-operation (nop) instructions, ensuring they coexist within a single fragment. By doing so, the assembler avoids generating a relocation when the operands for symbol arithmetic are contained entirely within one fragment, leading to cleaner object files.
In Details
The change in gas/config/tc-loongarch.c adds a linker_relax flag to the loongarch_cl_insn struct. The core logic update prevents the emission of a relocation if both addsy and subsy directives fall within the same fragment. This is achieved by checking that relaxed instructions and alignment nops are placed within the same fragment, thereby simplifying the relocation calculation for symbol arithmetic. This optimization aims to reduce the overhead associated with relocations when the calculation operands are locally contained.
- addsy
- An assembler directive used in LoongArch GAS to indicate the start of a symbol arithmetic expression, often involving labels. It's part of calculating relocations.
- subsy
- An assembler directive used in LoongArch GAS, typically paired with 'addsy', to complete a symbol arithmetic expression. Together, they define the operands for a relocation.
- Fragment
- A contiguous sequence of code or data within an object file that the assembler or linker treats as a unit. Relocations are often associated with fragments.
- Relocation
- Information in an object file that tells the linker how to adjust addresses or symbols to their final locations in memory.
- Linker-relaxable instructions
- Instructions whose final encoding might be determined or adjusted by the linker, often involving branch offsets or immediate values that depend on the final layout of the code.