Apparent miscompilation with -loop-index-split -loop-rotate -loop-reduce

[llvmbot]

Bugzilla Link	3089
Resolution	INVALID
Resolved on	Oct 08, 2010 10:20
Version	2.4
OS	Linux
Attachments	Test case
Reporter	LLVM Bugzilla Contributor

Extended Description

I believe the attached bitcode is miscompiled with "opt -loop-index-split -loop-rotate -loop-reduce bugpoint-tooptimize.bc" (bugpointed).

While I do not know for certain that the code is correct, it seems to run without segfaulting with almost any llvm options, including all the default -O levels. It also is production code used by lots of different people (usually compiled with gcc). However compiling with the mentioned passes causes the code to segfault. Architecture is amd64.

Please tell me if you need more information (source code, the whole program, whatever).

[llvmbot]

I see a bug in -loop-reduce.

[llvmbot]

Well, not really.

Do you have a small test case where we can reproduce the segfault ? Thanks.

[llvmbot]

Well, not really.

Do you have a small test case where we can reproduce the segfault ? Thanks.

The program I used to find this bug and the other bugs (mostly compiler crashes) I've lately reported is picosat, a MIT-licensed SAT solver not unlike minisat which seems to be a test case in llvm-test.

You can grab the source from

http://fmv.jku.at/picosat/picosat-846.tar.gz
.

After that I compiled the sources with llvm-gcc -emit-llvm (without optimization flags) and linked the bitcode files together with llvm-ld. Then I run opt with varying flags on the resulting bitcode.

If the (unoptimized) bitcode is enough for you, I'll attach it here (picosat.bc) together with a test input (test.cnf). Just run it with "picosat test.cnf" and you should get output like

---

$ ./picosat.my test.cnf
s SATISFIABLE
v -1 2 -3 4 -5 -6 -7 -8 -9 10 -11 -12 -13 -14 -15 -16 -17 -18 -19 -20 -21 -22
v -23 -24 -25 -26 -27 -28 -29 -30 -31 -32 -33 -34 -35 -36 -37 -38 -39 -40 -41
[... output continues ...]

[llvmbot]

picosat.bc, the test case program, unoptimized

[llvmbot]

Test input for picosat, run with "picosat test.cnf"

[llvmbot]

LoopIndexSplit pass has been removed from svn.