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Date: Thu, 17 Jul 2008 07:28:00 -0000
Subject: [Bug c++/36861]  New: code generation regression with -O3
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From: "lothar at tradescape dot biz" <gcc-bugzilla@gcc.gnu.org>
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gcc 4.3.1 generates code with -O3 that is more than 10 times slower than with
-O0. gcc 4.2.3 does not show this behavior. I am going to attach the test case
that I used to produce these numbers:

with gcc 4.2.3:
( time ./avltest-nn >/dev/null; time ./avltest-no >/dev/null; time ./avltest-on
>/dev/null; time ./avltest-oo >/dev/null; )

real    0m1.112s
user    0m1.028s
sys     0m0.012s

real    0m0.078s
user    0m0.060s
sys     0m0.008s

real    0m0.940s
user    0m0.916s
sys     0m0.008s

real    0m0.088s
user    0m0.072s
sys     0m0.004s


with gcc 4.3.1:
( time ./avltest-nn >/dev/null; time ./avltest-no >/dev/null; time ./avltest-on
>/dev/null; time ./avltest-oo >/dev/null; )

real    0m0.974s
user    0m0.948s
sys     0m0.004s

real    0m12.936s
user    0m12.893s
sys     0m0.016s

real    0m1.128s
user    0m1.012s
sys     0m0.000s

real    0m0.104s
user    0m0.076s
sys     0m0.004s

Here is the information about the compilers used:

$ /opt2/linux/ix86/bin/g++-4.2.3 -v
Using built-in specs.
Target: x86_64-pc-linux-gnu
Configured with: ../gcc-4.2.3/configure --program-suffix=-4.2.3
--enable-__cxa_atexit --enable-languages=c,c++,java --prefix=/opt2/linux/ix86
--target=x86_64-pc-linux-gnu --with-sysroot=/opt2/linux/ix86/gcc-sysroot
--enable-version-specific-runtime-libs --enable-clocale=gnu
Thread model: posix
gcc version 4.2.3

$ /opt2/linux/ix86/bin/g++-4.3.1 -v
Using built-in specs.
Target: x86_64-pc-linux-gnu
Configured with: ../gcc-4.3.1/configure --enable-targets=all --enable-multilib
--enable-__cxa_atexit --enable-languages=c,c++,java
--enable-version-specific-runtime-libs --disable-nls --enable-clocale=gnu
--program-suffix=-4.3.1 --prefix=/opt2/linux/ix86 --target=i686-pc-linux-gnu
--target=x86_64-pc-linux-gnu --with-sysroot=/opt2/linux/ix86/gcc-sysroot
Thread model: posix
gcc version 4.3.1 (GCC)


-- 
           Summary: code generation regression with -O3
           Product: gcc
           Version: 4.3.1
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: lothar at tradescape dot biz
GCC target triplet: x86_64-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36861