[lld][InstrProf] Skip BP ordering input sections with null data

[ellishg]

In MachO, .bss isecs have a length, but point to null. This causes Balanced Partitioning to crash on these inputs.

This code was in the original implementation, but was removed in https://github.com/llvm/llvm-project/pull/124482/files#diff-b2aac8833d29d297ae5ada1b36eb4e88f53691fd91df954c24e0c264f3131d4aL27

[llvmbot]

@llvm/pr-subscribers-lld

@llvm/pr-subscribers-lld-macho

Author: Ellis Hoag (ellishg)

Changes

In MachO, .bss isecs have a length, but point to null. This causes Balanced Partitioning to crash on these inputs.

This code was in the original implementation, but was removed in https://github.com/llvm/llvm-project/pull/124482/files#diff-b2aac8833d29d297ae5ada1b36eb4e88f53691fd91df954c24e0c264f3131d4aL27

---

Full diff: https://github.com/llvm/llvm-project/pull/137906.diff

2 Files Affected:

• (modified) lld/MachO/BPSectionOrderer.cpp (+1-1)
• (modified) lld/test/MachO/bp-section-orderer.s (+4)

diff --git a/lld/MachO/BPSectionOrderer.cpp b/lld/MachO/BPSectionOrderer.cpp
index 1295d21cad8a1..ca273f7f798dc 100644
--- a/lld/MachO/BPSectionOrderer.cpp
+++ b/lld/MachO/BPSectionOrderer.cpp
@@ -115,7 +115,7 @@ DenseMap<const InputSection *, int> lld::macho::runBalancedPartitioning(
     for (auto *sec : file->sections) {
       for (auto &subsec : sec->subsections) {
         auto *isec = subsec.isec;
-        if (!isec || isec->data.empty())
+        if (!isec || isec->data.empty() || !isec->data.data())
           continue;
         // ConcatInputSections are entirely live or dead, so the offset is
         // irrelevant.
diff --git a/lld/test/MachO/bp-section-orderer.s b/lld/test/MachO/bp-section-orderer.s
index f3293b54dbcf1..93d0b85731de7 100644
--- a/lld/test/MachO/bp-section-orderer.s
+++ b/lld/test/MachO/bp-section-orderer.s
@@ -106,6 +106,10 @@ r3:
 r4:
   .quad s2
 
+.bss
+bss0:
+  .zero 10
+
 .subsections_via_symbols
 
 #--- a.proftext