langhooks.h (LANG_HOOKS_HONOR_READONLY): New macro.

	* langhooks.h (LANG_HOOKS_HONOR_READONLY): New macro.
	* toplev.h (struct lang_hooks): New field HONOR_READONLY.
	* emit-rtl.c (set_mem_attributes): Set RTX_UNCHANGING_P from
	TREE_READONLY and TYPE_READONLY if lang_hooks.honor_readonly.
	Set alignment from type if INDIRECT_REF.
	(adjust_address_1, offset_address): Simplify alignment compuitation.
	* expr.c (expand_expr, case INDIRECT_REF): Don't set RTX_UNCHANGING_P
	here; done by set_mem_attributes.

From-SVN: r46361

5 files changed, 31 insertions, 25 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 69bc79dcd82..0c724c34456 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,14 @@
+Fri Oct 19 15:24:39 2001  Richard Kenner  <kenner@vlsi1.ultra.nyu.edu>
+
+	* langhooks.h (LANG_HOOKS_HONOR_READONLY): New macro.
+	* toplev.h (struct lang_hooks): New field HONOR_READONLY.
+	* emit-rtl.c (set_mem_attributes): Set RTX_UNCHANGING_P from
+	TREE_READONLY and TYPE_READONLY if lang_hooks.honor_readonly.
+	Set alignment from type if INDIRECT_REF.
+	(adjust_address_1, offset_address): Simplify alignment compuitation.
+	* expr.c (expand_expr, case INDIRECT_REF): Don't set RTX_UNCHANGING_P
+	here; done by set_mem_attributes.
+
 2001-10-19  Kaveh R. Ghazi  <ghazi@caip.rutgers.edu>
 
 	* Makefile.in (rtlanal.o): Depend on $(TM_P_H).
diff --git a/gcc/emit-rtl.c b/gcc/emit-rtl.c
index c7c61401b5e..45fd406f4c9 100644
--- a/gcc/emit-rtl.c
+++ b/gcc/emit-rtl.c
@@ -1672,13 +1672,11 @@ set_mem_attributes (ref, t, objectp)
      front-end routine).  */
   set_mem_alias_set (ref, get_alias_set (t));
 
-  /* It is incorrect to set RTX_UNCHANGING_P from TREE_READONLY (type)
-     here, because, in C and C++, the fact that a location is accessed
-     through a const expression does not mean that the value there can
-     never change.  */
-
   MEM_VOLATILE_P (ref) = TYPE_VOLATILE (type);
   MEM_IN_STRUCT_P (ref) = AGGREGATE_TYPE_P (type);
+  RTX_UNCHANGING_P (ref)
+    |= (lang_hooks.honor_readonly
+	&& (TYPE_READONLY (type) || TREE_READONLY (t)));
 
   /* If we are making an object of this type, we know that it is a scalar if
      the type is not an aggregate.  */
@@ -1717,6 +1715,10 @@ set_mem_attributes (ref, t, objectp)
 	 ? GEN_INT (tree_low_cst (TYPE_SIZE_UNIT (TREE_TYPE (t)), 1))
 	 : 0, DECL_ALIGN (t) / BITS_PER_UNIT);
 
+  /* If this is an INDIRECT_REF, we know its alignment.  */
+  if (TREE_CODE (t) == INDIRECT_REF)
+    set_mem_align (ref, TYPE_ALIGN (type) / BITS_PER_UNIT);
+
   /* Now see if we can say more about whether it's an aggregate or
      scalar.  If we already know it's an aggregate, don't bother.  */
   if (MEM_IN_STRUCT_P (ref))
@@ -1860,14 +1862,11 @@ adjust_address_1 (memref, mode, offset, validate)
   if (memoffset)
     memoffset = GEN_INT (offset + INTVAL (memoffset));
 
-  /* If the offset is negative, don't try to update the alignment.  If it's
-     zero, the alignment hasn't changed.  Otherwise, the known alignment may
-     be less strict.  */
-  if (offset < 0)
-    memalign = 1;
-
-  while (offset > 0 && (offset % memalign) != 0)
-    memalign >>= 1;
+  /* Compute the new alignment by taking the MIN of the alignment and the
+     lowest-order set bit in OFFSET, but don't change the alignment if OFFSET
+     if zero.  */
+  if (offset != 0)
+    memalign = MIN (memalign, offset & -offset);
 
   MEM_ATTRS (new)
     = get_mem_attrs (MEM_ALIAS_SET (memref), MEM_DECL (memref), memoffset,
@@ -1893,15 +1892,11 @@ offset_address (memref, offset, pow2)
   rtx new = change_address_1 (memref, VOIDmode,
 			      gen_rtx_PLUS (Pmode, XEXP (memref, 0),
 					    force_reg (Pmode, offset)), 1);
-  unsigned int memalign = MEM_ALIGN (memref);
 
   /* Update the alignment to reflect the offset.  Reset the offset, which
      we don't know.  */
-  while (pow2 % memalign != 0)
-    memalign >>= 1;
-
   MEM_ATTRS (new) = get_mem_attrs (MEM_ALIAS_SET (memref), MEM_DECL (memref),
-				   0, 0, memalign);
+				   0, 0, MIN (MEM_ALIGN (memref), pow2));
   return new;
 }
   
diff --git a/gcc/expr.c b/gcc/expr.c
index f486b32e4fd..3290b39496d 100644
--- a/gcc/expr.c
+++ b/gcc/expr.c
@@ -6812,13 +6812,6 @@ expand_expr (exp, target, tmode, modifier)
 	temp = gen_rtx_MEM (mode, op0);
 	set_mem_attributes (temp, exp, 0);
 
-	/* It is incorrect to set RTX_UNCHANGING_P from TREE_READONLY
-	   here, because, in C and C++, the fact that a location is accessed
-	   through a pointer to const does not mean that the value there can
-	   never change.  Languages where it can never change should
-	   also set TREE_STATIC.  */
-	RTX_UNCHANGING_P (temp) = TREE_READONLY (exp) & TREE_STATIC (exp);
-
 	/* If we are writing to this object and its type is a record with
 	   readonly fields, we must mark it as readonly so it will
 	   conflict with readonly references to those fields.  */
diff --git a/gcc/langhooks.h b/gcc/langhooks.h
index 43335fa2ba6..e3067fb2611 100644
--- a/gcc/langhooks.h
+++ b/gcc/langhooks.h
@@ -39,6 +39,9 @@ Boston, MA 02111-1307, USA.  */
 #ifndef LANG_HOOKS_POST_OPTIONS
 #define LANG_HOOKS_POST_OPTIONS NULL
 #endif
+#ifndef LANG_HOOKS_HONOR_READONLY
+#define LANG_HOOKS_HONOR_READONLY 0
+#endif
 
 /* Declarations of default tree inlining hooks.  */
 tree tree_inlining_default_hook_walk_subtrees PARAMS ((tree*, int *,
@@ -108,6 +111,7 @@ int tree_inlining_default_hook_anon_aggr_type_p PARAMS ((tree));
   LANG_HOOKS_INIT_OPTIONS, \
   LANG_HOOKS_DECODE_OPTION, \
   LANG_HOOKS_POST_OPTIONS, \
+  LANG_HOOKS_HONOR_READONLY, \
   LANG_HOOKS_TREE_INLINING_INITIALIZER \
 }
 
diff --git a/gcc/toplev.h b/gcc/toplev.h
index 72fa2fd640a..c9b60ee2c3e 100644
--- a/gcc/toplev.h
+++ b/gcc/toplev.h
@@ -166,6 +166,9 @@ struct lang_hooks
   /* Called when all command line options have been processed.  */
   void (*post_options) PARAMS ((void));
 
+  /* Nonzero if TYPE_READONLY and TREE_READONLY should always be honored.  */
+  int honor_readonly;
+
   struct lang_hooks_for_tree_inlining tree_inlining;
 
   /* Whenever you add entries here, make sure you adjust langhooks.h