* Makefile.in (CRTSTUFF_CFLAGS): Add -fno-zero-initialized-in-bss.

	* doc/invoke.texi (-fno-zero-initialized-in-bss): Document.
	* flags.h (flag_zero_initialized_in_bss): Declare.
	* toplev.c (flag_zero_initialized_in_bss): New flag.
	(lang_independent_options): Add flag_zero_initialized_in_bss.
	* tree.c (initializer_zerop): New function.
	* tree.h (initializer_zerop): Declare.
	* varasm.c (assemble_variable): If we can emit bss, put zero
	initializers in the bss section.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@50218 138bc75d-0d04-0410-961f-82ee72b054a4

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 22056f2..bd9ce0f 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,15 @@
+2002-03-01  Kaveh R. Ghazi  <ghazi@caip.rutgers.edu>
+
+       * Makefile.in (CRTSTUFF_CFLAGS): Add -fno-zero-initialized-in-bss.
+       * doc/invoke.texi (-fno-zero-initialized-in-bss): Document.
+       * flags.h (flag_zero_initialized_in_bss): Declare.
+       * toplev.c (flag_zero_initialized_in_bss): New flag.
+       (lang_independent_options): Add flag_zero_initialized_in_bss.
+       * tree.c (initializer_zerop): New function.
+       * tree.h (initializer_zerop): Declare.
+       * varasm.c (assemble_variable): If we can emit bss, put zero
+       initializers in the bss section.
+
 2002-03-02  Alan Modra  <amodra@bigpond.net.au>
 
        * config/rs6000/rs6000.h (ASM_WEAKEN_DECL): AIX assembler doesn't

diff --git a/gcc/Makefile.in b/gcc/Makefile.in
index 604dd7d..5d1802f 100644 (file)
--- a/gcc/Makefile.in
+++ b/gcc/Makefile.in
@@ -372,7 +372,8 @@ TARGET_LIBGCC2_CFLAGS =
 
 # Options to use when compiling crtbegin/end.
 CRTSTUFF_CFLAGS = -O2 $(GCC_CFLAGS) $(INCLUDES) $(MULTILIB_CFLAGS) -g0 \
-  -finhibit-size-directive -fno-inline-functions -fno-exceptions
+  -finhibit-size-directive -fno-inline-functions -fno-exceptions \
+  -fno-zero-initialized-in-bss
 
 # Additional sources to handle exceptions; overridden on ia64.
 LIB2ADDEH = $(srcdir)/unwind-dw2.c $(srcdir)/unwind-dw2-fde.c \

diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 8dab7a0..10b69c8 100644 (file)
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -273,6 +273,7 @@ in the following sections.
 -fno-function-cse  -fno-guess-branch-probability @gol
 -fno-inline  -fno-math-errno  -fno-peephole  -fno-peephole2 @gol
 -funsafe-math-optimizations -fno-trapping-math @gol
+-fno-zero-initialized-in-bss @gol
 -fomit-frame-pointer  -foptimize-register-move @gol
 -foptimize-sibling-calls  -fprefetch-loop-arrays @gol
 -freduce-all-givs -fregmove  -frename-registers @gol
@@ -3407,6 +3408,19 @@ an exact implementation of IEEE or ISO rules/specifications for
 math functions.
 
 The default is @option{-ftrapping-math}.
+
+@item -fno-zero-initialized-in-bss
+@opindex fno-zero-initialized-in-bss
+If the target supports a BSS section, GCC by default puts variables that
+are initialized to zero into BSS@.  This can save space in the resulting
+code.
+
+This option turns off this behavior because some programs explicitly
+rely on variables going to the data section.  E.g., so that the
+resulting executable can find the beginning of that section and/or make
+assumptions based on that.
+
+The default is @option{-fzero-initialized-in-bss}.
 @end table
 
 The following options control specific optimizations.  The @option{-O2}

diff --git a/gcc/flags.h b/gcc/flags.h
index 65353e6..6de5d9b 100644 (file)
--- a/gcc/flags.h
+++ b/gcc/flags.h
@@ -636,4 +636,7 @@ extern int flag_detailed_statistics;
 /* Nonzero means enable synchronous exceptions for non-call instructions.  */
 extern int flag_non_call_exceptions;
 
+/* Nonzero means put zero initialized data in the bss section.  */
+extern int flag_zero_initialized_in_bss;
+
 #endif /* ! GCC_FLAGS_H */

diff --git a/gcc/toplev.c b/gcc/toplev.c
index 83de908..7460582 100644 (file)
--- a/gcc/toplev.c
+++ b/gcc/toplev.c
@@ -803,6 +803,9 @@ int flag_gnu_linker = 0;
 int flag_gnu_linker = 1;
 #endif
 
+/* Nonzero means put zero initialized data in the bss section.  */
+int flag_zero_initialized_in_bss = 1;
+
 /* Enable SSA.  */
 int flag_ssa = 0;
 
@@ -1135,6 +1138,8 @@ static const lang_independent_options f_options[] =
    N_("Suppress output of instruction numbers and line number notes in debugging dumps") },
   {"instrument-functions", &flag_instrument_function_entry_exit, 1,
    N_("Instrument function entry/exit with profiling calls") },
+  {"zero-initialized-in-bss", &flag_zero_initialized_in_bss, 1,
+   N_("Put zero initialized data in the bss section") },
   {"ssa", &flag_ssa, 1,
    N_("Enable SSA optimizations") },
   {"ssa-ccp", &flag_ssa_ccp, 1,

diff --git a/gcc/tree.c b/gcc/tree.c
index 5e0210b..de65191 100644 (file)
--- a/gcc/tree.c
+++ b/gcc/tree.c
@@ -4975,3 +4975,45 @@ make_vector (mode, innertype, unsignedp)
 
   return t;
 }
+
+/* Given an initializer INIT, return TRUE if INIT is zero or some
+   aggregate of zeros.  Otherwise return FALSE.  */
+
+bool
+initializer_zerop (init)
+     tree init;
+{
+  STRIP_NOPS (init);
+
+  switch (TREE_CODE (init))
+    {
+    case INTEGER_CST:
+      return integer_zerop (init);
+    case REAL_CST:
+      return real_zerop (init)
+       && ! REAL_VALUE_MINUS_ZERO (TREE_REAL_CST (init));
+    case COMPLEX_CST:
+      return integer_zerop (init)
+       || (real_zerop (init)
+           && ! REAL_VALUE_MINUS_ZERO (TREE_REAL_CST (TREE_REALPART (init)))
+           && ! REAL_VALUE_MINUS_ZERO (TREE_REAL_CST (TREE_IMAGPART (init))));
+    case CONSTRUCTOR:
+      {
+       if (AGGREGATE_TYPE_P (TREE_TYPE (init)))
+       {
+         tree aggr_init = TREE_OPERAND (init, 1);
+         
+         while (aggr_init)
+           {
+             if (! initializer_zerop (TREE_VALUE (aggr_init)))
+               return false;
+             aggr_init = TREE_CHAIN (aggr_init);
+           }
+         return true;
+       }
+       return false;
+      }
+    default:
+      return false;
+    }
+}

diff --git a/gcc/tree.h b/gcc/tree.h
index b13fc53..68b96e8 100644 (file)
--- a/gcc/tree.h
+++ b/gcc/tree.h
@@ -2495,6 +2495,11 @@ extern int list_length                   PARAMS ((tree));
 
 extern int fields_length               PARAMS ((tree));
 
+/* Given an initializer INIT, return TRUE if INIT is zero or some
+   aggregate of zeros.  Otherwise return FALSE.  */
+
+extern bool initializer_zerop          PARAMS ((tree));
+
 /* integer_zerop (tree x) is nonzero if X is an integer constant of value 0 */
 
 extern int integer_zerop               PARAMS ((tree));

diff --git a/gcc/varasm.c b/gcc/varasm.c
index f8fb16c..e7505a8 100644 (file)
--- a/gcc/varasm.c
+++ b/gcc/varasm.c
@@ -1608,7 +1608,12 @@ assemble_variable (decl, top_level, at_end, dont_output_data)
 
   /* Handle uninitialized definitions.  */
 
-  if ((DECL_INITIAL (decl) == 0 || DECL_INITIAL (decl) == error_mark_node)
+  if ((DECL_INITIAL (decl) == 0 || DECL_INITIAL (decl) == error_mark_node
+#if defined ASM_EMIT_BSS
+       || (flag_zero_initialized_in_bss
+          && initializer_zerop (DECL_INITIAL (decl)))
+#endif
+       )
       /* If the target can't output uninitialized but not common global data
         in .bss, then we have to use .data.  */
 #if ! defined ASM_EMIT_BSS