rtl.h (initialize_uninitialized_subregs): New prototype.

2001-12-04  Andrew MacLeod  <amacleod@redhat.com>

	* rtl.h (initialize_uninitialized_subregs): New prototype.
	* toplev.c (rest_of_compilation): Call initialize_uninitialized_subregs
	when optimization is on.
	* flow.c (find_regno_partial): Find subregs within an expression.
	(initialize_uninitialized_subregs): Initialize live on entry registers
	which are used in subreg expressions.

From-SVN: r47644

4 files changed, 132 insertions, 3 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 7996d8b..b390614 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,12 @@
+2001-12-04  Andrew MacLeod  <amacleod@redhat.com>
+
+	* rtl.h (initialize_uninitialized_subregs): New prototype.
+	* toplev.c (rest_of_compilation): Call initialize_uninitialized_subregs
+	when optimization is on.
+	* flow.c (find_regno_partial): Find subregs within an expression.
+	(initialize_uninitialized_subregs): Initialize live on entry registers
+	which are used in subreg expressions.
+
 2001-12-04  Phil Edwards  <pme@gcc.gnu.org>
 
 	* Makefile.in:  Add INSTALL_SCRIPT using INSTALL definition.
diff --git a/gcc/flow.c b/gcc/flow.c
index fdf4df2..cf7d4a0 100644
--- a/gcc/flow.c
+++ b/gcc/flow.c
@@ -306,6 +306,8 @@ static void mark_set_regs		PARAMS ((struct propagate_block_info *,
 static void mark_set_1			PARAMS ((struct propagate_block_info *,
 						 enum rtx_code, rtx, rtx,
 						 rtx, int));
+static int find_regno_partial		PARAMS ((rtx *, void *));
+
 #ifdef HAVE_conditional_execution
 static int mark_regno_cond_dead		PARAMS ((struct propagate_block_info *,
 						 int, rtx));
@@ -1290,6 +1292,112 @@ calculate_global_regs_live (blocks_in, blocks_out, flags)
 
   free (queue);
 }
+
+
+/* This structure is used to pass parameters to an from the
+   the function find_regno_partial(). It is used to pass in the 
+   register number we are looking, as well as to return any rtx 
+   we find.  */
+
+typedef struct {
+  unsigned regno_to_find;
+  rtx retval;
+} find_regno_partial_param;
+
+
+/* Find the rtx for the reg numbers specified in 'data' if it is
+   part of an expression which only uses part of the register.  Return
+   it in the structure passed in.  */
+static int 
+find_regno_partial (ptr, data)
+     rtx *ptr;
+     void *data;
+{
+  find_regno_partial_param *param = (find_regno_partial_param *)data;
+  unsigned reg = param->regno_to_find;
+  param->retval = NULL_RTX;
+
+  if (*ptr == NULL_RTX)
+    return 0;
+
+  switch (GET_CODE (*ptr)) 
+    {
+      case ZERO_EXTRACT:
+      case SIGN_EXTRACT:
+      case STRICT_LOW_PART:
+        if (GET_CODE (XEXP (*ptr, 0)) == REG && REGNO (XEXP (*ptr, 0)) == reg)
+	  {
+	    param->retval = *ptr;
+	    return 1;
+	  }
+	break;
+
+      case SUBREG:
+        if (GET_CODE (SUBREG_REG (*ptr)) == REG 
+	    && REGNO (SUBREG_REG (*ptr)) == reg)
+	  {
+	    param->retval = *ptr;
+	    return 1;
+	  }
+	break;
+    }
+
+  return 0;
+}
+
+/* Process all immediate successors of the entry block looking for pseudo
+   registers which are live on entry. Find all of those whose first 
+   instance is a partial register reference of some kind, and initialize 
+   them to 0 after the entry block.  This will prevent bit sets within
+   registers whose value is unknown, and may contain some kind of sticky 
+   bits we don't want.  */
+
+int
+initialize_uninitialized_subregs () 
+{
+  rtx insn;
+  edge e;
+  int reg, did_something = 0;
+  find_regno_partial_param param;
+
+  for (e = ENTRY_BLOCK_PTR->succ; e; e = e->succ_next)
+    {
+      basic_block bb = e->dest;
+      regset map = bb->global_live_at_start;
+      EXECUTE_IF_SET_IN_REG_SET (map,
+				 FIRST_PSEUDO_REGISTER, reg,
+	{
+	  int uid = REGNO_FIRST_UID (reg);
+	  rtx i;
+
+	  /* Find an insn which mentions the register we are looking for.
+	     Its preferable to have an instance of the register's rtl since
+	     there may be various flags set which we need to duplicate.  
+	     If we can't find it, its probably an automatic whose initial
+	     value doesnt matter, or hopefully something we dont care about. */
+	  for (i = get_insns (); i && INSN_UID (i) != uid; i = NEXT_INSN (i))
+	    ;
+	  if (i != NULL_RTX)
+	    {
+	      /* Found the insn, now get the REG rtx, if we can.  */
+	      param.regno_to_find = reg;
+	      for_each_rtx (&i, find_regno_partial, &param);
+	      if (param.retval != NULL_RTX)
+		{
+		  insn = gen_move_insn (param.retval, 
+				        CONST0_RTX (GET_MODE (param.retval)));
+		  insert_insn_on_edge (insn, e);
+		  did_something = 1;
+		}
+	    }
+	});
+    }
+
+  if (did_something)
+    commit_edge_insertions ();
+  return did_something;
+}
+
 
 /* Subroutines of life analysis.  */
 
diff --git a/gcc/rtl.h b/gcc/rtl.h
index baafcdc..b76376a 100644
--- a/gcc/rtl.h
+++ b/gcc/rtl.h
@@ -1903,10 +1903,11 @@ extern void move_by_pieces		PARAMS ((rtx, rtx,
 						 unsigned int));
 
 /* In flow.c */
-extern void recompute_reg_usage		PARAMS ((rtx, int));
+extern void recompute_reg_usage			PARAMS ((rtx, int));
+extern int initialize_uninitialized_subregs	PARAMS ((void));
 #ifdef BUFSIZ
-extern void print_rtl_with_bb		PARAMS ((FILE *, rtx));
-extern void dump_flow_info		PARAMS ((FILE *));
+extern void print_rtl_with_bb			PARAMS ((FILE *, rtx));
+extern void dump_flow_info			PARAMS ((FILE *));
 #endif
 
 /* In expmed.c */
diff --git a/gcc/toplev.c b/gcc/toplev.c
index 54582dc..fc2e8b6 100644
--- a/gcc/toplev.c
+++ b/gcc/toplev.c
@@ -3017,6 +3017,17 @@ rest_of_compilation (decl)
 	setjmp_args_warning ();
     }
 
+  if (optimize)
+    {
+      if (initialize_uninitialized_subregs ())
+	{
+	  /* Insns were inserted, so things might look a bit different.  */
+	  insns = get_insns();
+	  life_analysis (insns, rtl_dump_file, 
+			 (PROP_LOG_LINKS | PROP_REG_INFO | PROP_DEATH_NOTES));
+	}
+    }
+
   close_dump_file (DFI_life, print_rtl_with_bb, insns);
 
   ggc_collect ();