[all-commits] [llvm/llvm-project] 283c47: [lld][LoongArch] GOT indirection to PC relative op...

[Zhaoxin Yang via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 283c47b4c5231a1baf528355f7119a73ac168968
      https://github.com/llvm/llvm-project/commit/283c47b4c5231a1baf528355f7119a73ac168968
  Author: Zhaoxin Yang <yangzhaoxin at loongson.cn>
  Date:   2025-08-01 (Fri, 01 Aug 2025)

  Changed paths:
    M lld/ELF/Arch/LoongArch.cpp
    A lld/test/ELF/loongarch-pc-hi20-lo12-got.s
    M lld/test/ELF/loongarch-relax-pc-hi20-lo12.s

  Log Message:
  -----------
  [lld][LoongArch] GOT indirection to PC relative optimization (#123743)

In LoongArch, we try GOT indirection to PC relative optimization in
normal or medium code model, whether or not with R_LARCH_RELAX
relocation.

From:
* pcalau12i $a0, %got_pc_hi20(sym_got)
* ld.w/d $a0, $a0, %got_pc_lo12(sym_got)

To:
* pcalau12i $a0, %pc_hi20(sym)
* addi.w/d $a0, $a0, %pc_lo12(sym)

If the original code sequence can be relaxed into a single instruction
`pcaddi`, this patch will not be taken (see
https://github.com/llvm/llvm-project/pull/123566).
The optimization related to GOT is split into two locations because the
`relax()` function is part of an iteration fixed-point algorithm. We
should minimize it to achieve better linker performance.
    
Note: Althouth the optimization has been performed, the GOT entries
still exists, similarly to AArch64. Eliminating the entries will
increase code complexity.



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