Index: ELF/ICF.cpp
===================================================================
--- ELF/ICF.cpp
+++ ELF/ICF.cpp
@@ -188,6 +188,12 @@
   if (S->Name == ".init" || S->Name == ".fini")
     return false;
 
+  // A user program may enumerate sections named with a C identifier using
+  // __start_* and __stop_* symbols. We cannot ICF any such sections because
+  // that could change program semantics.
+  if (isValidCIdentifier(S->Name))
+    return false;
+
   return true;
 }
 
Index: test/ELF/icf-c-identifier.s
===================================================================
--- test/ELF/icf-c-identifier.s
+++ test/ELF/icf-c-identifier.s
@@ -0,0 +1,9 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
+# RUN: ld.lld %t -o %t2 --icf=all --print-icf-sections | count 0
+
+.section foo,"ax",@progbits,unique,0
+.byte 42
+
+.section foo,"ax",@progbits,unique,1
+.byte 42
Index: test/ELF/icf-different-output-sections.s
===================================================================
--- test/ELF/icf-different-output-sections.s
+++ test/ELF/icf-different-output-sections.s
@@ -2,8 +2,8 @@
 # RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
 # RUN: ld.lld %t -o %t2 --icf=all --print-icf-sections | count 0
 
-.section foo,"ax"
+.section .foo,"ax"
 .byte 42
 
-.section bar,"ax"
+.section .bar,"ax"
 .byte 42