[Bug tree-optimization/22000] [4.0/4.1 Regression] Read from volatile member of struct is optimized away

[joseph at codesourcery dot com]

------- Additional Comments From joseph at codesourcery dot com  2005-06-23 16:59 -------
Subject: Re:  [4.0/4.1 Regression] Read from
 volatile member of struct is optimized away

On Thu, 23 Jun 2005, mmitchel at gcc dot gnu dot org wrote:

> I somewhat suspect this hunk of code in c-typeck.c:build_component_ref:
> 
> 	  if (TREE_THIS_VOLATILE (datum) || TREE_THIS_VOLATILE (subdatum))
> 	    TREE_THIS_VOLATILE (ref) = 1;
> 
> I don't see anything that sets TREE_SIDE_EFFECTS.

In general TREE_SIDE_EFFECTS is set by the low-level tree-building code in 
tree.c (if set for the operands of a tree) so front ends need only change 
it if the defaults are wrong.

>    If this bit is set in an expression, so is TREE_SIDE_EFFECTS.  */
>    #define TREE_THIS_VOLATILE(NODE) ((NODE)->common.volatile_flag)

This does seem like something tree checking could usefully be added for.



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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22000