Index: lld/ELF/ICF.cpp
===================================================================
--- lld/ELF/ICF.cpp
+++ lld/ELF/ICF.cpp
@@ -219,10 +219,12 @@
     size_t mid = bound - sections.begin();
 
     // Now we split [Begin, End) into [Begin, Mid) and [Mid, End) by
-    // updating the sections in [Begin, Mid). We use Mid as an equivalence
-    // class ID because every group ends with a unique index.
+    // updating the sections in [Begin, Mid). We use Mid as the basis for
+    // the equivalence class ID because every group ends with a unique index.
+    // Set MSB to 1 to avoid equality with "unique" IDs.
+    uint32_t eqClass = mid | (1U << 31);
     for (size_t i = begin; i < mid; ++i)
-      sections[i]->eqClass[next] = mid;
+      sections[i]->eqClass[next] = eqClass;
 
     // If we created a group, we need to iterate the main loop again.
     if (mid != end)
@@ -471,7 +473,7 @@
   uint32_t uniqueId = 0;
   for (Partition &part : partitions)
     part.ehFrame->iterateFDEWithLSDA<ELFT>(
-        [&](InputSection &s) { s.eqClass[0] = ++uniqueId; });
+        [&](InputSection &s) { s.eqClass[0] = s.eqClass[1] = ++uniqueId; });
 
   // Collect sections to merge.
   for (InputSectionBase *sec : inputSections) {
@@ -481,8 +483,10 @@
   }
 
   // Initially, we use hash values to partition sections.
-  parallelForEach(
-      sections, [&](InputSection *s) { s->eqClass[0] = xxHash64(s->data()); });
+  parallelForEach(sections, [&](InputSection *s) {
+    // Set MSB to 1 to avoid collisions with non-hash IDs.
+    s->eqClass[0] = xxHash64(s->data()) | (1U << 31);
+  });
 
   // Perform 2 rounds of relocation hash propagation. 2 is an empirical value to
   // reduce the average sizes of equivalence classes, i.e. segregate() which has