[lld] r309232 - Make __start_sec __end_sec handling more precise.

[Rafael Espindola via llvm-commits]

Author: rafael
Date: Wed Jul 26 16:39:10 2017
New Revision: 309232

URL: http://llvm.org/viewvc/llvm-project?rev=309232&view=rev
Log:
Make __start_sec __end_sec handling more precise.

With this we only ask LTO to keep a C named section if there is a
__start_ or __end symbol.

This is not as strict as lld's --gc-sections, but is as good as we can
get without having a far more detailed ir summary.

Modified:
    lld/trunk/ELF/LTO.cpp
    lld/trunk/ELF/LTO.h
    lld/trunk/test/ELF/lto/section-name.ll

Modified: lld/trunk/ELF/LTO.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/LTO.cpp?rev=309232&r1=309231&r2=309232&view=diff
==============================================================================
--- lld/trunk/ELF/LTO.cpp (original)
+++ lld/trunk/ELF/LTO.cpp Wed Jul 26 16:39:10 2017
@@ -11,6 +11,7 @@
 #include "Config.h"
 #include "Error.h"
 #include "InputFiles.h"
+#include "SymbolTable.h"
 #include "Symbols.h"
 #include "lld/Core/TargetOptionsCommandFlags.h"
 #include "llvm/ADT/STLExtras.h"
@@ -107,7 +108,14 @@ static std::unique_ptr<lto::LTO> createL
                                      Config->LTOPartitions);
 }
 
-BitcodeCompiler::BitcodeCompiler() : LTOObj(createLTO()) {}
+BitcodeCompiler::BitcodeCompiler() : LTOObj(createLTO()) {
+  for (Symbol *Sym : Symtab->getSymbols()) {
+    StringRef Name = Sym->body()->getName();
+    for (StringRef Prefix : {"__start_", "__stop_"})
+      if (Name.startswith(Prefix))
+        UsedStartStop.insert(Name.substr(Prefix.size()));
+  }
+}
 
 BitcodeCompiler::~BitcodeCompiler() = default;
 
@@ -138,7 +146,7 @@ void BitcodeCompiler::add(BitcodeFile &F
 
     R.VisibleToRegularObj = Sym->IsUsedInRegularObj ||
                             (R.Prevailing && Sym->includeInDynsym()) ||
-                            isValidCIdentifier(ObjSym.getSectionName());
+                            UsedStartStop.count(ObjSym.getSectionName());
     if (R.Prevailing)
       undefine(Sym);
     R.LinkerRedefined = Config->RenamedSymbols.count(Sym);

Modified: lld/trunk/ELF/LTO.h
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/LTO.h?rev=309232&r1=309231&r2=309232&view=diff
==============================================================================
--- lld/trunk/ELF/LTO.h (original)
+++ lld/trunk/ELF/LTO.h Wed Jul 26 16:39:10 2017
@@ -22,6 +22,7 @@
 #define LLD_ELF_LTO_H
 
 #include "lld/Core/LLVM.h"
+#include "llvm/ADT/DenseSet.h"
 #include "llvm/ADT/SmallString.h"
 #include <memory>
 #include <vector>
@@ -50,6 +51,7 @@ private:
   std::unique_ptr<llvm::lto::LTO> LTOObj;
   std::vector<SmallString<0>> Buff;
   std::vector<std::unique_ptr<MemoryBuffer>> Files;
+  llvm::DenseSet<StringRef> UsedStartStop;
 };
 } // namespace elf
 } // namespace lld

Modified: lld/trunk/test/ELF/lto/section-name.ll
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/lto/section-name.ll?rev=309232&r1=309231&r2=309232&view=diff
==============================================================================
--- lld/trunk/test/ELF/lto/section-name.ll (original)
+++ lld/trunk/test/ELF/lto/section-name.ll Wed Jul 26 16:39:10 2017
@@ -7,5 +7,21 @@ target datalayout = "e-m:e-i64:64-f80:12
 target triple = "x86_64-unknown-linux-gnu"
 
 @foo = hidden global i32 42, section "foo_section"
+ at bar = hidden global i32 42, section "bar_section"
+ at zed = hidden global i32 42, section "zed_section"
 
-; CHECK: foo_section PROGBITS
+ at __start_foo_section = external global i32
+ at __stop_bar_section = external global i32
+
+define i32* @use1() {
+  ret i32* @__start_foo_section
+}
+
+define i32* @use2() {
+  ret i32* @__stop_bar_section
+}
+
+; CHECK-NOT: zed_section
+; CHECK:     foo_section PROGBITS
+; CHECK-NEXT:     bar_section PROGBITS
+; CHECK-NOT: zed_section