[gold][patch] Don't put symbols dropped by the plugin in the symbol tables

[Rafael Avila de Espindola <rafael.espindola@gmail.com>]

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The attached patch avoids putting symbols in the symbol tables if there 
are only found in IL files. This is important for when LTO manages to 
drop some symbols completely.

When linking libxul it reduces the final .so from 39339456 bytes to 
34450128 bytes. And yes, firefox still works :-)

2010-02-17  Rafael Ávila de Espíndola <respindola@mozilla.com>

	* symtab.cc (Symbol::should_add_dynsym_entry) Return false for
	plugin only symbols.
	(Symbol_table::sized_finalize_symbol) Mark symbol only present
	in plugin files as not needed in the symbol table.

Cheers,
Rafael


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diff --git a/gold/symtab.cc b/gold/symtab.cc
index cb650fb..d4ac297 100644
--- a/gold/symtab.cc
+++ b/gold/symtab.cc
@@ -310,6 +310,11 @@ Sized_symbol<size>::allocate_common(Output_data* od, Value_type value)
 inline bool
 Symbol::should_add_dynsym_entry(Symbol_table* symtab) const
 {
+  // If the symbol is only present on plugin files, the plugin decided we
+  // don't need it.
+  if (!this->in_real_elf())
+    return false;
+
   // If the symbol is used by a dynamic relocation, we need to add it.
   if (this->needs_dynsym_entry())
     return true;
@@ -2593,6 +2598,15 @@ Symbol_table::sized_finalize_symbol(Symbol* unsized_sym)
       return false;
     }
 
+  // If the symbol is only present on plugin files, the plugin decided we
+  // don't need it.
+  if (!sym->in_real_elf())
+    {
+      gold_assert(!sym->has_symtab_index());
+      sym->set_symtab_index(-1U);
+      return false;
+    }
+
   // Compute final symbol value.
   Compute_final_value_status status;
   Value_type value = this->compute_final_value(sym, &status);