Re: c/9853: [3.2/3.3/3.4 regression] miscompilation of non-constant structure initializer

[Glen Nakamura <glen at imodulo dot com>]

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=9853

After looking at the test case for PR c/9853, I believe the problem deals
with assigning and freeing temp slots while emitting the initializer.
In this case, the temp slot created by assign_temp in expand_expr (expr.c:7087)
is freed early by free_temp_slots in expand_decl_init (stmt.c:4061) and then
overwritten when a new temp slot is allocated.

I don't really understand how the different temp slot functions are intended
to be used, but the call to free_temp_slots at the end of expand_decl_init
didn't make sense to me because expand_assignment manages its own temp slots
using the push/free/pop functions.  Anyway, the following patch fixes the
problem (bootstrapped and regtested on i686-pc-linux-gnu 3.3 branch):

	* stmt.c (expand_decl_init): Remove redundant call to free_temp_slots.

diff -Nru3p gcc-3.3.orig/gcc/stmt.c gcc-3.3/gcc/stmt.c
--- gcc-3.3.orig/gcc/stmt.c	2003-02-22 10:04:10.000000000 +0000
+++ gcc-3.3/gcc/stmt.c	2003-02-22 10:04:10.000000000 +0000
@@ -4055,10 +4055,6 @@ expand_decl_init (decl)
 
   /* Don't let the initialization count as "using" the variable.  */
   TREE_USED (decl) = was_used;
-
-  /* Free any temporaries we made while initializing the decl.  */
-  preserve_temp_slots (NULL_RTX);
-  free_temp_slots ();
 }
 
 /* CLEANUP is an expression to be executed at exit from this binding contour;



Although the above patch fixes the problem, perhaps changing the keep argument
to the assign_temp in expand_expr would be safer?  I'll let someone who
understands the temp slot functions better decide.

diff -Nru10p gcc-3.3.orig/gcc/expr.c gcc-3.3/gcc/expr.c
--- gcc-3.3.orig/gcc/expr.c	2003-03-05 00:14:33.000000000 +0000
+++ gcc-3.3/gcc/expr.c	2003-03-05 00:14:33.000000000 +0000
@@ -7082,21 +7082,21 @@ expand_expr (exp, target, tmode, modifie
 	  /* Handle calls that pass values in multiple non-contiguous
 	     locations.  The Irix 6 ABI has examples of this.  */
 	  if (target == 0 || ! safe_from_p (target, exp, 1)
 	      || GET_CODE (target) == PARALLEL
 	      || modifier == EXPAND_STACK_PARM)
 	    target
 	      = assign_temp (build_qualified_type (type,
 						   (TYPE_QUALS (type)
 						    | (TREE_READONLY (exp)
 						       * TYPE_QUAL_CONST))),
-			     0, TREE_ADDRESSABLE (exp), 1);
+			     1, TREE_ADDRESSABLE (exp), 1);
 
 	  store_constructor (exp, target, 0, int_expr_size (exp));
 	  return target;
 	}
 
     case INDIRECT_REF:
       {
 	tree exp1 = TREE_OPERAND (exp, 0);
 	tree index;
 	tree string = string_constant (exp1, &index);

Attachment: testcase.c
Description: Text document