[Bug optimization/14907] New: bogus sign/zero extension when relaying parameters with regparm

[Bug optimization/14907] New: bogus sign/zero extension when relaying parameters with regparm

[cesarb at nitnet dot com dot br]

(this seem to be another case of the general bug of "the compiler doesn't know
when it has already extended the value")

This is the "other side" of PR 14903

When compiling:
extern void __attribute__((__regparm__(3))) f(unsigned char x);
void __attribute__((__regparm__(3))) g(unsigned char x) { f(x); }

With:
gcc -W -Wall -Os -fomit-frame-pointer -save-temps -c

The result is:
g:
        movzbl  %al, %eax
        jmp     f

Notice again the bogus zero extension (sign extension with signed char). The
same happens with shorts.

While PR 14903 can cause excessive stack usage, this one just looks dumb in the
assembly output.

Reading specs from /usr/lib/gcc-lib/i486-linux/3.3.3/specs
Configured with: ../src/configure -v
--enable-languages=c,c++,java,f77,pascal,objc,ada,treelang --prefix=/usr
--mandir=/usr/share/man --infodir=/usr/share/info
--with-gxx-include-dir=/usr/include/c++/3.3 --enable-shared --with-system-zlib
--enable-nls --without-included-gettext --enable-__cxa_atexit
--enable-clocale=gnu --enable-debug --enable-java-gc=boehm
--enable-java-awt=xlib --enable-objc-gc i486-linux
Thread model: posix
gcc version 3.3.3 (Debian 20040401)

-- 
           Summary: bogus sign/zero extension when relaying parameters with
                    regparm
           Product: gcc
           Version: 3.3.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: cesarb at nitnet dot com dot br
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14907

[Bug target/14907] bogus sign/zero extension when relaying parameters with regparm

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-04-10 15:31 -------
Confirmed.  I think this is requied by the ABI to promote it but since it is already promoted it could just 
use the full register, I do not know if this is really a bug but then again I could be wrong.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
          Component|optimization                |target
     Ever Confirmed|                            |1
           Keywords|                            |pessimizes-code
   Last reconfirmed|0000-00-00 00:00:00         |2004-04-10 15:31:46
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14907

[Bug optimization/14907] bogus sign/zero extension when relaying parameters with regparm

[cesarb at nitnet dot com dot br]

------- Additional Comments From cesarb at nitnet dot com dot br  2004-04-10 15:56 -------
regparm is a different (gcc-specific) version of the ABI right? (But someone
should check if the bogus extensions happen when loading the arguments from the
stack too, and check if they are really bogus when reading from the stack).

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|target                      |optimization


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14907

[Bug target/14907] bogus sign/zero extension when relaying parameters with regparm

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-07-10 01:28 -------
Basically the problem is that the RTL optimizers do not know if they come in as full 32bit register even 
though the ABI demands it.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|2004-04-10 15:31:46         |2004-07-10 01:28:55
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14907

[Bug target/14907] bogus sign/zero extension when relaying parameters with regparm

[nmiell at comcast dot net]

------- Comment #4 from nmiell at comcast dot net  2006-03-01 05:54 -------
This also occurs on AMD64 without any special attributes (the ABI passes params
in registers already).

When compiling:
extern char c2(char);
char c1(char c) { return c2(c); }

with gcc -Wall -O2 -S tail-char.c
using gcc (GCC) 4.0.2 20051125 (Red Hat 4.0.2-8)

The result is:
c1:
        subq    $8, %rsp
        movsbl  %dil,%edi
        call    c2
        addq    $8, %rsp
        movsbl  %al,%eax
        ret


-- 

nmiell at comcast dot net changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |nmiell at comcast dot net


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14907