Fix merge-by-content to not merge atoms with different custom sections

[kledzik]

Summary

The mergeByContent attribute on atoms triggers the symbol table to coalesce atoms with the exact same content. The problem is that atoms can also have a required custom section. The coalescing should never change the custom section of an atom.

The fix is to only consider to atoms to have the same content if their sectionChoice() and customSectionName() attributes match.

[ruiu]

LGTM

[kledzik]

committed in r218893

lib/Core/SymbolTable.cpp

   if (l == getTombstoneKey())
     return false;
   if (r == getTombstoneKey())
     return false;
   if (l->contentType() != r->contentType())
     return false;
   if (l->size() != r->size())
     return false;
+  if (l->sectionChoice() != r->sectionChoice())
+    return false;
+  if (l->sectionChoice() == DefinedAtom::sectionCustomRequired) {
+    if (!l->customSectionName().equals(r->customSectionName()))
+      return false;
+  }
   ArrayRef<uint8_t> lc = l->rawContent();
   ArrayRef<uint8_t> rc = r->rawContent();
   return memcmp(lc.data(), rc.data(), lc.size()) == 0;
 }
 
 bool SymbolTable::addByContent(const DefinedAtom &newAtom) {
   AtomContentSet::iterator pos = _contentTable.find(&newAtom);
   if (pos == _contentTable.end()) {

test/core/custom-section-coalesce.objtxt

+# RUN: lld -core %s | FileCheck %s
+
+#
+# Test that custom sections are preserved when duplicate merge-by-content
+# constants are coalesced.
+#
+
+---
+defined-atoms:
+    - ref-name:          L1
+      type:              constant
+      merge:             by-content
+      content:           [ 01, 02, 03, 04 ]
+      section-choice:    custom-required
+      section-name:      .mysection
+
+    - ref-name:          L2
+      type:              constant
+      merge:             by-content
+      content:           [ 05, 06, 07, 08 ]
+      section-choice:    custom-required
+      section-name:      .mysection
+
+    - ref-name:          L3
+      type:              constant
+      merge:             by-content
+      content:           [ 01, 02, 03, 04 ]
+
+---
+defined-atoms:
+    - ref-name:          L1
+      type:              constant
+      merge:             by-content
+      content:           [ 01, 02, 03, 04 ]
+      section-choice:    custom-required
+      section-name:      .mysection
+
+    - ref-name:          L2
+      type:              constant
+      merge:             by-content
+      content:           [ 01, 02, 03, 04 ]
+      section-choice:    custom-required
+      section-name:      .mysection2
+---
+defined-atoms:
+    - ref-name:          L1
+      type:              constant
+      merge:             by-content
+      content:           [ 05, 06, 07, 08 ]
+      section-choice:    custom-required
+      section-name:      .mysection
+
+    - ref-name:          L2
+      type:              constant
+      merge:             by-content
+      content:           [ 01, 02, 03, 04 ]
+...
+
+
+# CHECK:defined-atoms:
+# CHECK:  - type:            constant
+# CHECK:    content:         [ 01, 02, 03, 04 ]
+# CHECK:    merge:           by-content
+# CHECK:    section-choice:  custom-required
+# CHECK:    section-name:    .mysection
+# CHECK:  - type:            constant
+# CHECK:    content:         [ 05, 06, 07, 08 ]
+# CHECK:    merge:           by-content
+# CHECK:    section-choice:  custom-required
+# CHECK:    section-name:    .mysection
+# CHECK:  - type:            constant
+# CHECK:    content:         [ 01, 02, 03, 04 ]
+# CHECK:    merge:           by-content
+# CHECK:  - type:            constant
+# CHECK:    content:         [ 01, 02, 03, 04 ]
+# CHECK:    merge:           by-content
+# CHECK:    section-choice:  custom-required
+# CHECK:    section-name:    .mysection2