[ELF] Improve comment of InputSection::file and update getFile. NFC

[MaskRay]

Clarify a comment after #78944.

All uses of getFile() assert file is non-null. getFile is not used with a
synthetic section. Replace cast_or_null with cast.

[llvmbot]

@llvm/pr-subscribers-lld-elf

@llvm/pr-subscribers-lld

Author: Fangrui Song (MaskRay)

Changes

Clarify a comment after #78944.

All uses of getFile() assert file is non-null. It is not used with a
synthetic section. Replace cast_or_null with cast.

---

Full diff: https://github.com/llvm/llvm-project/pull/79550.diff

1 Files Affected:

• (modified) lld/ELF/InputSection.h (+5-4)

diff --git a/lld/ELF/InputSection.h b/lld/ELF/InputSection.h
index dda4242d8be1c1f..bb9dff38ae02995 100644
--- a/lld/ELF/InputSection.h
+++ b/lld/ELF/InputSection.h
@@ -118,9 +118,9 @@ class InputSectionBase : public SectionBase {
 
   static bool classof(const SectionBase *s) { return s->kind() != Output; }
 
-  // The file which contains this section. Its dynamic type is always
-  // ObjFile<ELFT>, but in order to avoid ELFT, we use InputFile as
-  // its static type.
+  // The file which contains this section. Its dynamic type is usually
+  // ObjFile<ELFT>, but may be an InputFile of InternalKind (for a synthetic
+  // section).
   InputFile *file;
 
   // Input sections are part of an output section. Special sections
@@ -132,8 +132,9 @@ class InputSectionBase : public SectionBase {
   // Section index of the relocation section if exists.
   uint32_t relSecIdx = 0;
 
+  // Getter when the dynamic type is ObjFile<ELFT>.
   template <class ELFT> ObjFile<ELFT> *getFile() const {
-    return cast_or_null<ObjFile<ELFT>>(file);
+    return cast<ObjFile<ELFT>>(file);
   }
 
   // Used by --optimize-bb-jumps and RISC-V linker relaxation temporarily to

[smithp35]

LGTM, may be worth seeing if nga888 is happy with it too.

[nga888]

LGTM too!