https://llvm.org/bugs/show_bug.cgi?id=26843
Bug ID: 26843
Summary: wrong code at -Os and above 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 -Os and above 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 262590)
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 -O1 small.c; ./a.out
$ clang-3.7 -Os small.c; ./a.out
$
$ clang-trunk -Os small.c
$ ./a.out
Aborted (core dumped)
$
---------------------------------
int a, b[4], c;
void
fn1 ()
{
b[1] = 1;
if (a)
for (a = 1; a < 4; a++)
b[a] = 0;
a = 1;
}
int
main ()
{
for (; c < 2; c++)
fn1 ();
if (b[1] != 0)
__builtin_abort ();
return 0;
}
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