Hello Ian,
Tuesday, July 3, 2007, 6:23:02 PM, you wrote:
> Adding a new field to mem_attrs could be a problem. You'll have to
> measure to see how much the memory usage changes.
We have tested that previously with alias-export patch, which uses the
same mechanism for saving original exprs for rtl.
It showed that the change in cc1-i-files compile time was less than 1%,
memory usage change was negligible. We'll do the test again with the
new patch, though I don't think the memory consumption will increase.
>> +/* If EXPR contains conversions at the root of the tree, all of them
>> + will be removed. */
>> +
>> +static tree
>> +skip_conversions (tree expr)
>> +{
>> + tree inner = expr;
>> + /* Remove any conversions: they don't change what the underlying
>> + object is. Likewise for SAVE_EXPR. */
>> + while (TREE_CODE (inner) == NOP_EXPR || TREE_CODE (inner) == CONVERT_EXPR
>> + || TREE_CODE (inner) == NON_LVALUE_EXPR
>> + || TREE_CODE (inner) == VIEW_CONVERT_EXPR
>> + || TREE_CODE (inner) == SAVE_EXPR)
>> + inner = TREE_OPERAND (inner, 0);
>> + return inner;
>> +}
> I don't understand why it's OK to throw all these away. Some of them
> change the meaning of the expression. I also don't understand why you
> want to throw them away.
This piece of code was actually derived from alias-export branch, and
is not needed for this project.
In alias-export we also used original expression trees to disambiguate
memory references. E.g. two mems with orig_exprs (t1) x and (t2 *) p
can be disambiguated if points-to for p doesn't contain x. Here it
doesn't matter what types x and p have, so we used skip_conversions to
simplify disambiguation routines logic. The cleanup from conversions
worked for alias-export, because when we later searched for the base
variable to take it's points-to, we never went through INDIRECT_REFs.
>> @@ -1401,27 +1456,36 @@ component_ref_for_mem_expr (tree ref)
...
>> }
> The handling of INDIRECT_REF here seems clearly wrong. You definitely
> can't discard conversions for an INDIRECT_REF.
I agree. This code should have been removed in early versions of
alias-export. We don't modify MEM_EXPR at all since MEM_ORIG_EXPR
was introduced.
--
Best regards,
Dmitry mailto:[EMAIL PROTECTED]
