https://llvm.org/bugs/show_bug.cgi?id=26860
Bug ID: 26860
Summary: wrong code at -O3 on x86_64-linux-gnu
Product: clang
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: normal
Priority: P
Component: -New Bugs
Assignee: unassignedclangb...@nondot.org
Reporter: s...@cs.ucdavis.edu
CC: llvm-bugs@lists.llvm.org
Classification: Unclassified
The following code is miscompiled by the current clang trunk on
x86_64-linux-gnu at -O3 in both the 32-bit and 64-bit modes.
This is a regression from 3.7.x.
$ clang-trunk -v
clang version 3.9.0 (trunk 262797)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /usr/local/tools/bin
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/4.9
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/4.9.3
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/5.3.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.4
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.4.7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.6
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.6.4
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.7.3
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.8
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.8.5
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9.3
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5.3.0
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Candidate multilib: x32;@mx32
Selected multilib: .;@m64
$
$ clang-trunk -O2 small.c; ./a.out
$ clang-3.7 -O3 small.c; ./a.out
$
$ clang-trunk -O3 small.c
$ ./a.out
Aborted (core dumped)
$
--------------------------------
int a[4], b[4], c, d;
char e;
void
fn1 ()
{
for (;; c++)
{
for (;;)
{
e = b[3];
if (e)
{
b[c] = 0;
break;
}
return;
}
a[3] = d = 1;
for (; d < 4; d++)
{
a[d] = 0;
if (b[3])
break;
}
}
}
int
main ()
{
b[3] = 1;
fn1 ();
if (a[3])
__builtin_abort ();
return 0;
}
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