COFF: Stop requiring comdat sections to have an external leader to participate in ICF.

This requirement was added in r254578 to fix pr25686. However, it
appears to have originated from a misdiagnosis of the problem: link.exe
refused to merge the two sections because they are non-executable,
not because they have internal leaders. If I set up a similar scenario
with functions instead of globals I see that link.exe merges them.

Differential Revision: https://reviews.llvm.org/D40236

llvm-svn: 318682

lld/COFF/ICF.cpp

@@ -82,10 +82,8 @@ bool ICF::isEligible(SectionChunk *C) {
   if (!C->isCOMDAT() || !C->isLive() || Writable)
     return false;
 
-  // Code sections with external symbols are eligible.
-  bool Global = C->Sym && C->Sym->isExternal();
-  bool Executable = C->getPermissions() & llvm::COFF::IMAGE_SCN_MEM_EXECUTE;
-  if (Global && Executable)
+  // Code sections are eligible.
+  if (C->getPermissions() & llvm::COFF::IMAGE_SCN_MEM_EXECUTE)
     return true;
 
   // .xdata unwind info sections are eligble.

lld/test/COFF/icf-executable.s

@@ -0,0 +1,18 @@
+# RUN: llvm-mc -triple=x86_64-windows-msvc %s -filetype=obj -o %t.obj
+# RUN: lld-link -entry:main %t.obj -out:%t.exe -verbose 2>&1 | FileCheck %s
+
+# CHECK: Selected internal
+# CHECK:   Removed f2
+
+.section .text,"xr",one_only,internal
+internal:
+.globl main
+main:
+call f2
+ret
+
+.section .text,"xr",one_only,f2
+.globl f2
+f2:
+call main
+ret