Modifying prolouge function in gcc

[Andrew Haley]

Nick Maclaren writes:
 > SandeepThorat <sathorat2003@yahoo.com> wrote:
 > >
 > >         i want to make some modification to prolouge(& epilouge) function of
 > > gcc compiler. I m using version 4.1.0. 
 > >
 > > Can anybody tel me out- which file contain these functions, How to make
 > > changes & how to recompile it to take effect.
 > 
 > I can tell you quite a lot of that, at least for the Intel x86, but
 > I failed to reverse engineer the source enough to make the changes
 > I wanted (even with help), and didn't have time to reverse engineer
 > the code generation.

Try this.  It won't work if __limit and __failure are in different
shared objects, but it should be OK otherwise.

Andrew.


Index: i386.c
===================================================================
--- i386.c	(revision 124185)
+++ i386.c	(working copy)
@@ -1536,6 +1536,7 @@
 static void ix86_compute_frame_layout (struct ix86_frame *);
 static bool ix86_expand_vector_init_one_nonzero (bool, enum machine_mode,
 						 rtx, rtx, int);
+static rtx ix86_expand_int_compare (enum rtx_code code, rtx op0, rtx op1);
 
 
 /* The svr4 ABI for the i386 says that records and unions are returned
@@ -5831,6 +5832,9 @@
 
 /* Expand the prologue into a bunch of separate insns.  */
 
+static GTY(()) rtx limit;
+static GTY(()) rtx failure_function;
+
 void
 ix86_expand_prologue (void)
 {
@@ -6020,6 +6024,38 @@
       REG_NOTES (insn) = gen_rtx_EXPR_LIST (REG_MAYBE_DEAD, const0_rtx, NULL);
     }
 
+  {
+    if (limit == NULL_RTX)
+      {
+	tree foo = build_decl (VAR_DECL, get_identifier ("__limit"),
+			       build_pointer_type (void_type_node));
+	DECL_EXTERNAL (foo) = true;
+	layout_decl (foo, 0);
+	rest_of_decl_compilation (foo, true, 0);
+	limit = DECL_RTL (foo);
+
+	foo = build_decl (FUNCTION_DECL, get_identifier ("__failure"),
+			  build_function_type (void_type_node, void_list_node));
+	DECL_EXTERNAL (foo) = true;
+	rest_of_decl_compilation (foo, true, 0);
+	failure_function = DECL_RTL (foo);
+      }
+
+    {
+      rtx label = gen_label_rtx ();
+      rtx tmp = ix86_expand_int_compare (GEU, stack_pointer_rtx, limit);
+      tmp = gen_rtx_IF_THEN_ELSE (VOIDmode, tmp,
+				  gen_rtx_LABEL_REF (VOIDmode, label),
+				  pc_rtx);
+      tmp = emit_jump_insn (gen_rtx_SET (VOIDmode, pc_rtx, tmp));
+      JUMP_LABEL (tmp) = label;
+      ix86_expand_call (NULL_RTX, failure_function,  const0_rtx,  constm1_rtx,
+			NULL_RTX, 0);
+      emit_label (label);
+      LABEL_NUSES (label) = 1;
+    }
+  }
+
   /* Prevent function calls from be scheduled before the call to mcount.
      In the pic_reg_used case, make sure that the got load isn't deleted.  */
   if (current_function_profile)