appalling optimisation with sub/cmp on i386

[Matthias Klose <doko@klose.in-berlin.de>]

>Submitter-Id:	net
>Originator:	herbert@gondor.apana.org.au
>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 75773-quiet@bugs.debian.org 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: