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From: Matthias Klose <doko@klose.in-berlin.de> To: gcc-gnats@gcc.gnu.org, debian-gcc@lists.debian.org Subject: optimization/3507: appalling optimisation with sub/cmp on i386 Date: Sun, 01 Jul 2001 09:16:00 -0000 [thread overview] Message-ID: <E15Gjl8-0002wb-00@gate.local> (raw) >Number: 3507 >Category: optimization >Synopsis: appalling optimisation with sub/cmp on i386 >Confidential: no >Severity: non-critical >Priority: low >Responsible: unassigned >State: open >Class: pessimizes-code >Submitter-Id: net >Arrival-Date: Sun Jul 01 09:16:00 PDT 2001 >Closed-Date: >Last-Modified: >Originator: herbert@gondor.apana.org.au >Release: 3.0 (Debian GNU/Linux) and HEAD 20010701 >Organization: The Debian project >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: >Release-Note: >Audit-Trail: >Unformatted:
next reply other threads:[~2001-07-01 9:16 UTC|newest] Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top 2001-07-01 9:16 Matthias Klose [this message] 2002-04-02 2:36 rth
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