[ELF] Filter out non InputSection members from InputSections

InputSections may contain MergeInputSection members which trigger
a segmentation fault when trying to cast them to InputSection.

Differential Revision: https://reviews.llvm.org/D33628

llvm-svn: 304189

lld/ELF/LinkerScript.cpp

@@ -291,6 +291,9 @@ LinkerScript::computeInputSections(const InputSectionDescription *Cmd) {
     size_t SizeBefore = Ret.size();
 
     for (InputSectionBase *Sec : InputSections) {
+      if (!isa<InputSection>(Sec))
+        continue;
+
       if (Sec->Assigned)
         continue;
 

lld/test/ELF/linkerscript/merge-sections.s

@@ -31,6 +31,16 @@
 # 0x19E = begin + sizeof(.foo) = 0x190 + 0xE
 # CHECK-NEXT: Value: 0x19E
 
+# Check that we don't crash with --gc-sections
+# RUN: ld.lld --gc-sections -o %t2 --script %t.script %t -shared
+# RUN: llvm-readobj -s -t %t2 | FileCheck %s --check-prefix=GC
+
+# GC:        Name: .foo
+# GC-NEXT:   Type: SHT_PROGBITS
+# GC-NEXT:   Flags [
+# GC-NEXT:     SHF_ALLOC
+# GC-NEXT:   ]
+
 .section        .foo.1a,"aMS",@progbits,1
 .asciz "foo"