[Bug other/17107] New: Opportunity to improve code generated for complex logical expression

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

Description:
A non-optimal code sequence is illustraded.    Duplicate using gcc 3.5 and
command line:

gcc -O3 -m64 -c test.c


Testcase:
int i;
void foo(int a, int b, int c) {

  i = (a > b && a < c);

}

Assembly:
Currently gcc 3.5 generates the following code which always results
in the execution of the compare/branch for the right side of the
expression (i.e. a < c):

.foo:
      cmpw 7,4,3
      cmpw 6,3,5
      ld 11,.LC0@toc(2)
      li 9,1
      blt- 7,.L2
      li 9,0
.L2:
      li 0,1
      blt- 6,.L3
      li 0,0
.L3:
      and 0,9,0
      stw 0,0(11)
      blr

Execution of the second compare/branch may be avoided by
restructuring the code.  This also eliminates the need for
the 'and':

.foo:
      cmpw 7,4,3
      ld 11,.LC0@toc(2)
      li 9,0
      bng- 7,.L2
      cmpw 6,3,5
      bnl- 6,.L2
      li 9,1
.L2:
      stw 9,0(11)
      blr



-- 
           Summary: Opportunity to improve code generated for complex
                    logical expression
           Product: gcc
           Version: 3.5.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P1
         Component: other
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: steinmtz at us dot ibm dot com
                CC: gcc-bugs at gcc dot gnu dot org,steinmtz at us dot ibm
                    dot com
 GCC build triplet: powerpc64-linux
  GCC host triplet: powerpc64-linux
GCC target triplet: powerpc64-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17107