[Bug tree-optimization/17549] [4.0 Regression] 10% increase in codesize with C code compared to GCC 3.3

["steven at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Additional Comments From steven at gcc dot gnu dot org  2005-02-07 23:13 -------
Using var_to_partition does not help.  The reason is that the SSA names with 
the same root var are not in the same partition, e.g. 
 
int 
foo (int x, int a, int b) 
{ 
  x = a + b; 
  x = x * a; 
  x = x * b; 
  return x; 
} 
 
--> 
 
Sorted Coalesce list: 
 
Partition map 
 
Partition 0 (x_3 - 3 ) 
Partition 1 (x_4 - 4 ) 
Partition 2 (x_5 - 5 ) 
 
After Coalescing: 
 
Partition map 
 
Partition 0 (a_1 - 1 ) 
Partition 1 (b_2 - 2 ) 
Partition 2 (x_3 - 3 ) 
Partition 3 (x_4 - 4 ) 
Partition 4 (x_5 - 5 ) 
Partition 5 (<retval>_7 - 7 ) 
 
 
Replacing Expressions 
x_3 replace with --> a_1 + b_2 
x_4 replace with --> a_1 * x_3 
x_5 replace with --> b_2 * x_4 
 
<retval>_7  --> <retval> 
x_3  --> x 
x_4 not coalesced with x -->  New temp:  'x.0' 
x_5 not coalesced with x.0 -->  New temp:  'x.1' 
b_2  --> b 
a_1  --> a 
After Root variable replacement: 
 
Partition map 
 
Partition 0 (a - 1 ) 
Partition 1 (b - 2 ) 
Partition 2 (x - 3 ) 
Partition 3 (x.0 - 4 ) 
Partition 4 (x.1 - 5 ) 
Partition 5 (<retval> - 7 ) 
 
So if you replace the root var comparison in my hack with a check to make sure 
def and def2 are not in the same partition, that whole check will always be 
false and you still get crap code. 
 

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17549