On Mon, Aug 23, 2010 at 02:46:21PM +0300, Revital1 Eres wrote:
> I'm compiling the following test with GCC 4.6.0 and I do not see that
> MAX_EXPR is generated for (num)<0)?0:(num).
> With GCC 4.3.2 it is generated OK in original dump (both compilation were
> made with -O3). Is there a flag I should use to generate MAX_EXPR
> with GCC 4.6.0?
>
> Thanks,
> Revital
>
> #define TEST(num) (unsigned char)(((num)>0xFF)?0xff:(((num)<0)?0:(num)))
>
> int foo(const unsigned char *tmp, int i, int val)
> {
> return TEST(tmp[i] + val);
> }
There are two issues here:
1) the (completely unnecessary here) narrowing cast to unsigned char
This prevents fold_cond_expr_with_comparison from being called, as
the arguments aren't equal. One is
((int)tmp[i]) + val, the other is tmp[i] + (unsigned char)val.
Unfortunately even fold_converting the comparison operand
to (unsigned char) doesn't yield something that would be
operand_equal_for_comparison_p.
2) without the unnecessary cast, MAX_EXPR is generated, but MIN_EXPR
around it is not. The problem is that the argument is not the same,
(it is the same as TREE_OPERAND (max_expr, 0)).
Jakub
