[lld] [lld][ELF] Support relax R_LARCH_ALIGN (PR #78692)

[Fangrui Song via llvm-commits]

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@@ -659,6 +663,156 @@ void LoongArch::relocate(uint8_t *loc, const Relocation &rel,
   }
 }
 
+static bool relax(InputSection &sec) {
+  const uint64_t secAddr = sec.getVA();
+  const MutableArrayRef<Relocation> relocs = sec.relocs();
+  auto &aux = *sec.relaxAux;
+  bool changed = false;
+  ArrayRef<SymbolAnchor> sa = ArrayRef(aux.anchors);
+  uint64_t delta = 0;
+
+  std::fill_n(aux.relocTypes.get(), relocs.size(), R_LARCH_NONE);
+  aux.writes.clear();
+  for (auto [i, r] : llvm::enumerate(relocs)) {
+    const uint64_t loc = secAddr + r.offset - delta;
+    uint32_t &cur = aux.relocDeltas[i], remove = 0;
+    switch (r.type) {
+    case R_LARCH_ALIGN: {
+      const uint64_t addend =
+          r.sym->isUndefined() ? Log2_64(r.addend) + 1 : r.addend;
+      const uint64_t allBytes = (1 << (addend & 0xff)) - 4;
+      const uint64_t align = 1 << (addend & 0xff);
+      const uint64_t maxBytes = addend >> 8;
+      const uint64_t off = loc & (align - 1);
+      const uint64_t curBytes = off == 0 ? 0 : align - off;
+      // All bytes beyond the alignment boundary should be removed.
+      // If emit bytes more than max bytes to emit, remove all.
+      if (maxBytes != 0 && curBytes > maxBytes)
+        remove = allBytes;
+      else
+        remove = allBytes - curBytes;
+      assert(static_cast<int32_t>(remove) >= 0 &&
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MaskRay wrote:

RISC-V has changed this to an `errorOrWarn`

https://github.com/llvm/llvm-project/pull/78692