[Bug optimization/2962] unnecessary instruction cwtl

[debian-gcc at lists dot debian dot org]

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=2962


debian-gcc at lists dot debian dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |herbert at gondor dot apana
                   |                            |dot org dot au


------- Additional Comments From debian-gcc at lists dot debian dot org  2003-08-10 15:28 -------
Herbert Xu writes:

I appologise for all the reopening.  Be rest assured that your efforts 
in gettings these issues addressed is most appreciated. 
 
Unfortunately as in other cases this bug hasn't been addressed in 
full by the upstream.  Although the cwtl instructions are gone, it has 
been replaced by the equivalent mov?wl: 
 
-- a.c -- 
#include <ctype.h> 
 
int a(short i) { 
        return i & 1; 
} 
 
int foo(int c) { 
        return isdigit(c); 
} 
-- 
 
-- gcc -S -O2 a.c -- 
a: 
        pushl   %ebp 
        movl    %esp, %ebp 
        movswl  8(%ebp),%eax 
        andl    $1, %eax 
        leave 
        ret 
 
... 
 
foo: 
        pushl   %ebp 
        movl    %esp, %ebp 
        subl    $8, %esp 
        call    __ctype_b_loc 
        movl    (%eax), %edx 
        movl    8(%ebp), %eax 
        movzwl  (%edx,%eax,2), %eax 
        andl    $2048, %eax 
        leave 
        ret 
        .size   foo, .-foo 
        .ident  "GCC: (GNU) 3.3 20030509 (Debian prerelease)" 
 
In both instances the extension (mov?wl) is unnecessary as 
it is followed immediately by an and which zaps the high bits.