[lld] [lld][macho] Use reloc length correctly in hash computation (PR #165287)

[Ellis Hoag via llvm-commits]

https://github.com/ellishg created https://github.com/llvm/llvm-project/pull/165287

`Reloc::length` actually encodes the log2 of the length. Thanks @int3 for pointing this out in https://github.com/llvm/llvm-project/issues/160894#issuecomment-3416250179.

This code computes hashes of relocations. With the correct length, the hashes should more accurately represent the relocation. In my testing of some large binaries, the compressed size change is negligable.

>From 8ead45438fb8bf3ea7e7ee975805353963d13487 Mon Sep 17 00:00:00 2001
From: Ellis Hoag <ellis.sparky.hoag at gmail.com>
Date: Mon, 27 Oct 2025 10:34:02 -0700
Subject: [PATCH] [lld][macho] Use reloc length correctly in hash computation

---
 lld/MachO/BPSectionOrderer.cpp | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/lld/MachO/BPSectionOrderer.cpp b/lld/MachO/BPSectionOrderer.cpp
index 1f07ea9caf5df..d50abc22fc6c1 100644
--- a/lld/MachO/BPSectionOrderer.cpp
+++ b/lld/MachO/BPSectionOrderer.cpp
@@ -61,12 +61,13 @@ struct BPOrdererMachO : lld::BPOrderer<BPOrdererMachO> {
 
     // Calculate relocation hashes
     for (const auto &r : sec.relocs) {
-      if (r.length == 0 || r.referent.isNull() || r.offset >= data.size())
+      uint32_t relocLength = 1 << r.length;
+      if (r.referent.isNull() || r.offset + relocLength > data.size())
         continue;
 
       uint64_t relocHash = getRelocHash(r, sectionToIdx);
       uint32_t start = (r.offset < windowSize) ? 0 : r.offset - windowSize + 1;
-      for (uint32_t i = start; i < r.offset + r.length; i++) {
+      for (uint32_t i = start; i < r.offset + relocLength; i++) {
         auto window = data.drop_front(i).take_front(windowSize);
         hashes.push_back(xxh3_64bits(window) ^ relocHash);
       }