ELF: Don't examine values of linker script symbols during ICF.

These symbols are declared early with the same value, so they otherwise
appear identical to ICF.

Differential Revision: https://reviews.llvm.org/D51376

llvm-svn: 340998

4 files changed, 22 insertions, 2 deletions

diff --git a/lld/ELF/ICF.cpp b/lld/ELF/ICF.cpp
index 075938bd16b..7c6440a410e 100644
--- a/lld/ELF/ICF.cpp
+++ b/lld/ELF/ICF.cpp
@@ -252,7 +252,10 @@ bool ICF<ELFT>::constantEq(const InputSection *SecA, ArrayRef<RelTy> RA,
 
     auto *DA = dyn_cast<Defined>(&SA);
     auto *DB = dyn_cast<Defined>(&SB);
-    if (!DA || !DB)
+
+    // Placeholder symbols generated by linker scripts look the same now but
+    // may have different values later.
+    if (!DA || !DB || DA->ScriptDefined || DB->ScriptDefined)
       return false;
 
     // Relocations referring to absolute symbols are constant-equal if their
diff --git a/lld/ELF/LinkerScript.cpp b/lld/ELF/LinkerScript.cpp
index c865e9bd6b1..9c35bb78ce1 100644
--- a/lld/ELF/LinkerScript.cpp
+++ b/lld/ELF/LinkerScript.cpp
@@ -209,6 +209,7 @@ static void declareSymbol(SymbolAssignment *Cmd) {
                          STT_NOTYPE, 0, 0, nullptr);
   Cmd->Sym = cast<Defined>(Sym);
   Cmd->Provide = false;
+  Sym->ScriptDefined = true;
 }
 
 // This method is used to handle INSERT AFTER statement. Here we rebuild
diff --git a/lld/ELF/Symbols.h b/lld/ELF/Symbols.h
index c3a958df2a1..dcfeb7f813e 100644
--- a/lld/ELF/Symbols.h
+++ b/lld/ELF/Symbols.h
@@ -164,7 +164,8 @@ protected:
       : File(File), NameData(Name.Data), NameSize(Name.Size), Binding(Binding),
         Type(Type), StOther(StOther), SymbolKind(K), NeedsPltAddr(false),
         IsInIplt(false), IsInIgot(false), IsPreemptible(false),
-        Used(!Config->GcSections), NeedsTocRestore(false) {}
+        Used(!Config->GcSections), NeedsTocRestore(false),
+        ScriptDefined(false) {}
 
 public:
   // True the symbol should point to its PLT entry.
@@ -187,6 +188,9 @@ public:
   // PPC64 toc pointer.
   unsigned NeedsTocRestore : 1;
 
+  // True if this symbol is defined by a linker script.
+  unsigned ScriptDefined : 1;
+
   // The Type field may also have this value. It means that we have not yet seen
   // a non-Lazy symbol with this name, so we don't know what its type is. The
   // Type field is normally set to this value for Lazy symbols unless we saw a
@@ -376,6 +380,7 @@ void replaceSymbol(Symbol *S, ArgT &&... Arg) {
   S->ExportDynamic = Sym.ExportDynamic;
   S->CanInline = Sym.CanInline;
   S->Traced = Sym.Traced;
+  S->ScriptDefined = Sym.ScriptDefined;
 
   // Print out a log message if --trace-symbol was specified.
   // This is for debugging.
diff --git a/lld/test/ELF/linkerscript/icf.s b/lld/test/ELF/linkerscript/icf.s
new file mode 100644
index 00000000000..7c74458232a
--- /dev/null
+++ b/lld/test/ELF/linkerscript/icf.s
@@ -0,0 +1,11 @@
+# REQUIRES: x86
+
+# RUN: echo "foo = 1; bar = 2;" > %t.script
+# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t.o
+# RUN: ld.lld %t.o %t.script -o %t --icf=all --print-icf-sections | count 0
+
+.section .text.foo,"ax",@progbits
+jmp foo
+
+.section .text.bar,"ax",@progbits
+jmp bar