>Submitter-Id: net
>Originator: [EMAIL PROTECTED]
>Organization: The Debian project
>Confidential: no
>Synopsis: appalling optimisation with sub/cmp on i386
>Severity: non-critical
>Priority: low
>Category: optimization
>Class: pessimizes-code
>Release: 3.0 (Debian GNU/Linux) and HEAD 20010701
>Environment:
System: Debian GNU/Linux (testing/unstable)
Architecture: i686
host: i386-linux
build: i386-linux
target: i386-linux
configured with: ../src/configure -v
--enable-languages=c,c++,java,f77,proto,objc --prefix=/usr
--infodir=/share/info --mandir=/share/man --enable-shared --with-gnu-as
--with-gnu-ld --with-system-zlib --enable-long-long --enable-nls
--without-included-gettext --disable-checking --enable-threads=posix
--enable-java-gc=boehm --with-cpp-install-dir=bin --enable-objc-gc i386-linux
>Description:
[ Reported to the Debian BTS as report #75773.
Please CC [EMAIL PROTECTED] on replies.
Log of report can be found at http://bugs.debian.org/75773 ]
For the file
unsigned long foo(unsigned long a, unsigned long b) {
unsigned long c = a - b;
if (a < b) {
c += 100;
}
return c;
}
gcc -O2 -S generates (The cmpl after the subl is unnecessary):
.file "bug-75773.c"
.text
.align 2
.p2align 2,,3
.globl foo
.type foo,@function
foo:
pushl %ebp
movl %esp, %ebp
movl 8(%ebp), %edx
movl 12(%ebp), %eax
movl %edx, %ecx
subl %eax, %ecx
cmpl %eax, %edx
jae .L2
addl $100, %ecx
.L2:
movl %ecx, %eax
popl %ebp
ret
.Lfe1:
.size foo,.Lfe1-foo
.ident "GCC: (GNU) 3.1 20010701 (experimental)"
>How-To-Repeat:
>Fix:
