[PATCH] D138135: [lld][ELF] Support LoongArch

[Fangrui Song via Phabricator via llvm-commits]

MaskRay added inline comments.


================
Comment at: lld/ELF/Arch/LoongArch.cpp:88
+
+  // We must specially handle the cases when the low 12 bits of dest are seen
+  // as negative, because the instructions consuming it (ld, st, addi, etc.)
----------------
I was quite confused by the description, then I realized that I probably should just figure out the formula myself:)

I wonder whether it's clear if we remove these textual descriptions and focus on the deduction:

```
  // We have to check if the higher 32 bits need adjustment too, due to
  // the large code model access pattern:
  //
  //     pcalau12i       A, %foo_hi20(sym)        // b in [0,0xfff]
  //     addi.d          T, zero, %foo_lo12(sym)  // pageoff in [0,0xfff]
  //     lu32i.d         T, %foo64_lo20(sym)      // c in [0,0xfffff]
  //     lu52i.d         T, T, %foo64_hi12(sym)   // d in [0,0xfff]
  //     {ldx,stx,add}.* A, A, T
  //
  // If we treat the immediates in the operands as unsigned, the adjusted page
  // delta (return value) is b<<12 | c<<32 | d<<52.
  // We have (pageoff<0x800?pageoff:pageoff-0x1000+0x100000000) + ((b<0x80000?b:b-0x100000)<<12) + (c<<32) + (d<<52) = dest - page(pc).
  //
  // When pageoff is 0xfff, its contribution to dest-page(pc) is effectively 0xfff-0x1000 + 0x100000000 as the high 32-bits are
  // set by lu32i.d+lu52i.d, e.g.
  //
  //     addi.d    T, zero, -1  ; T = 0xfff'fffff'fffff'fff
  //     lu32i.d   T, 1         ; T = 0x000'00001'fffff'fff
  //     lu52i.d   T, T, -1     ; T = 0xfff'00001'fffff'fff
```


================
Comment at: lld/ELF/Arch/LoongArch.cpp:228
+
+static bool inputFileHasCode(const InputFile *f) {
+  for (auto *sec : f->getSections())
----------------
> We probably should change the parameter to a const reference.

Not done?


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D138135/new/

https://reviews.llvm.org/D138135