tree-ssa-live.c (remove_unused_scope_block_p): Keep variables that have value exprs.

* tree-ssa-live.c (remove_unused_scope_block_p): Keep variables
that have value exprs.

From-SVN: r148161

gcc/ChangeLog

 2009-06-04  Alexandre Oliva  <aoliva@redhat.com>
 
+	* tree-ssa-live.c (remove_unused_scope_block_p): Keep variables
+	that have value exprs.
+
+2009-06-04  Alexandre Oliva  <aoliva@redhat.com>
+
 	* dwarf2asm.c (dw2_force_const_mem): Defer creation of
 	declarations for constants until...
 	(dw2_output_indirect_constant_1): ... this point.

gcc/tree-ssa-live.c

@@ -435,6 +435,17 @@ remove_unused_scope_block_p (tree scope)
 	 will be output to file.  */
       if (TREE_CODE (*t) == FUNCTION_DECL)
 	unused = false;
+
+      /* If a decl has a value expr, we need to instantiate it
+	 regardless of debug info generation, to avoid codegen
+	 differences in memory overlap tests.  update_equiv_regs() may
+	 indirectly call validate_equiv_mem() to test whether a
+	 SET_DEST overlaps with others, and if the value expr changes
+	 by virtual register instantiation, we may get end up with
+	 different results.  */
+      else if (TREE_CODE (*t) == VAR_DECL && DECL_HAS_VALUE_EXPR_P (*t))
+	unused = false;
+
       /* Remove everything we don't generate debug info for.  */
       else if (DECL_IGNORED_P (*t))
 	{