[GOLD] Reduce size of class Symbol

[Alan Modra <amodra at gmail dot com>]

On 64-bit targets there is a 32-bit hole in symbol->u_, and another
due to symbol flags exceeding 32 bits.  By moving plt_offset into the
union hole, the total size of the class reduces by one 64-bit word.

How much does this save?  Well, most targets create symbols as a
Sized_symbol.  The patch reduces the size of a 64-bit Sized_symbol on
a 64-bit host from 88 bytes to 80 bytes, and a 32-bit Sized_symbol
from 80 bytes to 72 bytes.  On a typical 32-bit host, sizes are
unchanged.

OK, or should I not worry about memory on a C++ project?  ;)

	* symtab.h (Symbol): Move plt_offset_ to union u_ structs.
	Rearrange fields of u_ structs.
	(Symbol::has_plt_offset, plt_offset, set_plt_offset): Adjust
	to suit.
	* symtab.cc (Symbol::init_fields): Adjust to suit.

diff --git a/gold/symtab.cc b/gold/symtab.cc
index 7e0a3f8..8108e4a 100644
--- a/gold/symtab.cc
+++ b/gold/symtab.cc
@@ -60,7 +60,7 @@ Symbol::init_fields(const char* name, const char* version,
   this->symtab_index_ = 0;
   this->dynsym_index_ = 0;
   this->got_offsets_.init();
-  this->plt_offset_ = -1U;
+  this->u_.from_object.plt_offset = -1U;
   this->type_ = type;
   this->binding_ = binding;
   this->visibility_ = visibility;
diff --git a/gold/symtab.h b/gold/symtab.h
index d881026..95d2892 100644
--- a/gold/symtab.h
+++ b/gold/symtab.h
@@ -448,14 +448,14 @@ class Symbol
   // Return whether this symbol has an entry in the PLT section.
   bool
   has_plt_offset() const
-  { return this->plt_offset_ != -1U; }
+  { return this->u_.from_object.plt_offset != -1U; }
 
   // Return the offset into the PLT section of this symbol.
   unsigned int
   plt_offset() const
   {
     gold_assert(this->has_plt_offset());
-    return this->plt_offset_;
+    return this->u_.from_object.plt_offset;
   }
 
   // Set the PLT offset of this symbol.
@@ -463,7 +463,7 @@ class Symbol
   set_plt_offset(unsigned int plt_offset)
   {
     gold_assert(plt_offset != -1U);
-    this->plt_offset_ = plt_offset;
+    this->u_.from_object.plt_offset = plt_offset;
   }
 
   // Return whether this dynamic symbol needs a special value in the
@@ -988,33 +988,41 @@ class Symbol
     // This struct is used if SOURCE_ == FROM_OBJECT.
     struct
     {
+      // If this symbol has an entry in the PLT section, then this is the
+      // offset from the start of the PLT section.  This is -1U if there
+      // is no PLT entry.
+      unsigned int plt_offset;
+      // Section number in object in which symbol is defined.
+      unsigned int shndx;
       // Object in which symbol is defined, or in which it was first
       // seen.
       Object* object;
-      // Section number in object_ in which symbol is defined.
-      unsigned int shndx;
     } from_object;
 
     // This struct is used if SOURCE_ == IN_OUTPUT_DATA.
     struct
     {
+      // This field is common to all variants of this union
+      unsigned int plt_offset;
+      // True if the offset is from the end, false if the offset is
+      // from the beginning.
+      bool offset_is_from_end;
       // Output_data in which symbol is defined.  Before
       // Layout::finalize the symbol's value is an offset within the
       // Output_data.
       Output_data* output_data;
-      // True if the offset is from the end, false if the offset is
-      // from the beginning.
-      bool offset_is_from_end;
     } in_output_data;
 
     // This struct is used if SOURCE_ == IN_OUTPUT_SEGMENT.
     struct
     {
+      // This field is common to all variants of this union
+      unsigned int plt_offset;
+      // The base to use for the offset before Layout::finalize.
+      Segment_offset_base offset_base;
       // Output_segment in which the symbol is defined.  Before
       // Layout::finalize the symbol's value is an offset.
       Output_segment* output_segment;
-      // The base to use for the offset before Layout::finalize.
-      Segment_offset_base offset_base;
     } in_output_segment;
   } u_;
 
@@ -1035,11 +1043,6 @@ class Symbol
   // different TLS models), but will usually have at most one.
   Got_offset_list got_offsets_;
 
-  // If this symbol has an entry in the PLT section, then this is the
-  // offset from the start of the PLT section.  This is -1U if there
-  // is no PLT entry.
-  unsigned int plt_offset_;
-
   // Symbol type (bits 0 to 3).
   elfcpp::STT type_ : 4;
   // Symbol binding (bits 4 to 7).

-- 
Alan Modra
Australia Development Lab, IBM