[PATCH] D48389: [ELF] Move KeepUnique to InputSectionBase and update comments

[Sam Clegg via Phabricator via llvm-commits]

sbc100 created this revision.
Herald added subscribers: llvm-commits, aheejin, arichardson, emaste.
Herald added a reviewer: espindola.

KeepUnique is only ever used by InputSection.

Also, its seems that the Live bit is indeed used by output sections
as well as input ones.


Repository:
  rLLD LLVM Linker

https://reviews.llvm.org/D48389

Files:
  ELF/Driver.cpp
  ELF/InputSection.cpp
  ELF/InputSection.h


Index: ELF/InputSection.h
===================================================================
--- ELF/InputSection.h
+++ ELF/InputSection.h
@@ -52,18 +52,14 @@
 
   unsigned SectionKind : 3;
 
-  // The next two bit fields are only used by InputSectionBase, but we
-  // put them here so the struct packs better.
-
-  // The garbage collector sets sections' Live bits.
+  // The garbage collector sets the input sections' Live bits.
   // If GC is disabled, all sections are considered live by default.
+  // Output sections are live if they they have any input sections added to
+  // them.
   unsigned Live : 1;
 
   unsigned Bss : 1;
 
-  // Set for sections that should not be folded by ICF.
-  unsigned KeepUnique : 1;
-
   // These corresponds to the fields in Elf_Shdr.
   uint32_t Alignment;
   uint64_t Flags;
@@ -88,7 +84,7 @@
               uint64_t Entsize, uint64_t Alignment, uint32_t Type,
               uint32_t Info, uint32_t Link)
       : Name(Name), Repl(this), SectionKind(SectionKind), Live(false),
-        Bss(false), KeepUnique(false), Alignment(Alignment), Flags(Flags),
+        Bss(false), Alignment(Alignment), Flags(Flags),
         Entsize(Entsize), Type(Type), Link(Link), Info(Info) {}
 };
 
@@ -129,7 +125,10 @@
   // .foo takes all .text sections, and .bar becomes empty. To achieve
   // this, we need to memorize whether a section has been placed or
   // not for each input section.
-  bool Assigned = false;
+  unsigned Assigned : 1;
+
+  // Set for sections that should not be folded by ICF.
+  unsigned KeepUnique : 1;
 
   // Input sections are part of an output section. Special sections
   // like .eh_frame and merge sections are first combined into a
Index: ELF/InputSection.cpp
===================================================================
--- ELF/InputSection.cpp
+++ ELF/InputSection.cpp
@@ -60,7 +60,7 @@
                                    StringRef Name, Kind SectionKind)
     : SectionBase(SectionKind, Name, Flags, Entsize, Alignment, Type, Info,
                   Link),
-      File(File), Data(Data) {
+      File(File), Data(Data), Assigned(false), KeepUnique(false) {
   // In order to reduce memory allocation, we assume that mergeable
   // sections are smaller than 4 GiB, which is not an unreasonable
   // assumption as of 2017.
Index: ELF/Driver.cpp
===================================================================
--- ELF/Driver.cpp
+++ ELF/Driver.cpp
@@ -1191,10 +1191,13 @@
 static void findKeepUniqueSections(opt::InputArgList &Args) {
   for (auto *Arg : Args.filtered(OPT_keep_unique)) {
     StringRef Name = Arg->getValue();
-    if (auto *Sym = dyn_cast_or_null<Defined>(Symtab->find(Name)))
-      Sym->Section->KeepUnique = true;
-    else
-      warn("could not find symbol " + Name + " to keep unique");
+    if (auto *Sym = dyn_cast_or_null<Defined>(Symtab->find(Name))) {
+      if (auto *Sec = dyn_cast<InputSectionBase>(Sym->Section)) {
+        Sec->KeepUnique = true;
+        continue;
+      }
+    }
+    warn("could not find symbol " + Name + " to keep unique");
   }
 }
 


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