[Bug target/19672] [3.4/4.0/4.1 Regression] Performance regression in simple loop code

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

------- Comment #11 from bonzini at gcc dot gnu dot org  2005-10-18 10:07 -------
The code I get from -mbranch-cost=1 is extremely similar to what 3.2.2
produced:

.L7:
        cmpl    %ebx, %edi
        jae     .L2
        cmpl    %ecx, %esi
        jae     .L2
        decl    %ebx
        movsbl  -1(%ecx),%eax
        decl    %ecx
        movsbl  (%ebx),%edx
        subl    %eax, %edx
        movl    %edx, %eax
        je      .L7
.L2:

The front-end is correctly producing a TRUTH_AND_EXPR, i.e. the
short-circuiting is not required.  RTL expansion will use jae (short-circuited
evaluation) or seta, depending on the branch cost.

However, the tuning here is wrong because on a pentium4 I do get a 40% speedup
from -mbranch-cost=1.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19672