[PATCH, middle-end] A less inrusive patch to fix PR 37861 (Bogus array bounds warning)

[Martin Jambor <mjambor at suse dot cz>]

Hi,

my previous patch to fix this issue
(http://gcc.gnu.org/ml/gcc-patches/2008-11/msg00156.html) resulted in
a regression on m32c-unknown-elf reported in
http://gcc.gnu.org/ml/gcc/2008-11/msg00058.html.

Because we are quite late in  the development cycle and because my fix
might have been a bit too  pessimistic as it was, this a revised, less
restrictive patch that undoes my  previous one and then puts a bailout
at a different place, this time only when a char array is indexed by a
result of multiplication, which I assume is in fact a higher-dimension
indexing.  Not a very systematic approach but I could not come up with
anything better that would not break either PR 37861, PR 31982 and the
m32c problem reported by DJ.

I have bootstraped and tested it on x86_64-suse-linux, (rev. 141686)
OK for trunk?

Thanks,

Martin

2008-11-10  Martin Jambor  <mjambor@suse.cz>

	* tree-ssa-forwprop.c (forward_propagate_addr_expr_1): Do not check
	for INDIRECT_REFs.
	(forward_propagate_addr_into_variable_array_index): Check that the
	offset is not computed from a MULT_EXPR, use is_gimple_assign rather
	than the gimple code directly.
	

Index: gcc/tree-ssa-forwprop.c
===================================================================
--- gcc/tree-ssa-forwprop.c	(revision 141673)
+++ gcc/tree-ssa-forwprop.c	(working copy)
@@ -613,19 +613,27 @@ forward_propagate_addr_into_variable_arr
   tree index;
   gimple offset_def, use_stmt = gsi_stmt (*use_stmt_gsi);
 
-  /* Try to find an expression for a proper index.  This is either
-     a multiplication expression by the element size or just the
-     ssa name we came along in case the element size is one.  */
+  /* Get the offset's defining statement.  */
+  offset_def = SSA_NAME_DEF_STMT (offset);
+
+  /* Try to find an expression for a proper index.  This is either a
+     multiplication expression by the element size or just the ssa name we came
+     along in case the element size is one. In that case, however, we do not
+     allow multiplications because they can be computing index to a higher
+     level dimension (PR 37861). */
   if (integer_onep (TYPE_SIZE_UNIT (TREE_TYPE (TREE_TYPE (def_rhs)))))
-    index = offset;
-  else
     {
-      /* Get the offset's defining statement.  */
-      offset_def = SSA_NAME_DEF_STMT (offset);
+      if (is_gimple_assign (offset_def)
+	  && gimple_assign_rhs_code (offset_def) == MULT_EXPR)
+	return false;
 
+      index = offset;
+    }
+  else
+    {
       /* The statement which defines OFFSET before type conversion
          must be a simple GIMPLE_ASSIGN.  */
-      if (gimple_code (offset_def) != GIMPLE_ASSIGN)
+      if (!is_gimple_assign (offset_def))
 	return false;
 
       /* The RHS of the statement which defines OFFSET must be a
@@ -802,9 +810,6 @@ forward_propagate_addr_expr_1 (tree name
   array_ref = TREE_OPERAND (def_rhs, 0);
   if (TREE_CODE (array_ref) != ARRAY_REF
       || TREE_CODE (TREE_TYPE (TREE_OPERAND (array_ref, 0))) != ARRAY_TYPE
-      /* Avoid accessing hidden multidimensional arrays in this way or VRP
-	 might give out bogus warnings (see PR 37861) */
-      || TREE_CODE (TREE_OPERAND (array_ref, 0)) == INDIRECT_REF
       || !integer_zerop (TREE_OPERAND (array_ref, 1)))
     return false;