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Date: Sat, 10 Apr 2004 14:59:00 -0000
From: "cesarb at nitnet dot com dot br" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Message-ID: <20040410140503.14907.cesarb@nitnet.com.br>
Reply-To: gcc-bugzilla@gcc.gnu.org
Subject: [Bug optimization/14907] New: bogus sign/zero extension when relaying parameters with regparm
X-Bugzilla-Reason: CC
X-SW-Source: 2004-04/txt/msg00879.txt.bz2
List-Id: <gcc-bugs.sourceware.org>

(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