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[Bug target/18665] New: -ftrapv borks up simple integer arithmetic
- From: "skunk at iskunk dot org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 24 Nov 2004 22:28:05 -0000
- Subject: [Bug target/18665] New: -ftrapv borks up simple integer arithmetic
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
A large program was failing mysteriously on our new Opteron box. Went through it
with a fine-toothed debugger, until I came to the line
k -= i; /* <k> and <i> are ints */
Before this line: k == 2, i == 1
After this line: k == -14, i == 1
Compiling without -ftrapv makes this weirdness go away.
I will attach a tarball containing two .c files and a makefile, basically the
aforementioned big program with all irrelevant code ripped out---just enough to
reproduce the problem.
This bug first came up with 3.4.2, as shipped with Fedora Core 3 (x86-64). I
built 3.4.3 with the below configuration to confirm that the bug is still present.
Output from "gcc -v"
====================
Reading specs from
/mnt/freeport/opt/gcc-3.4.3--linux64/bin/../lib/gcc/x86_64-unknown-linux-gnu/3.4.3/specs
Configured with: /mnt/freeport/src/gcc/current/configure
--prefix=/mnt/freeport/arch/linux64 --disable-dependency-tracking
--disable-shared --disable-nls --with-libiconv-prefix=/mnt/freeport/arch/linux64
--disable-multilib --with-arch=opteron
Thread model: posix
gcc version 3.4.3
--
Summary: -ftrapv borks up simple integer arithmetic
Product: gcc
Version: 3.4.3
Status: UNCONFIRMED
Severity: critical
Priority: P2
Component: target
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: skunk at iskunk dot org
CC: gcc-bugs at gcc dot gnu dot org
GCC build triplet: x86_64-unknown-linux-gnu
GCC host triplet: x86_64-unknown-linux-gnu
GCC target triplet: x86_64-unknown-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18665