miscompile with -loop-rotate -indvars

[llvmbot]

Bugzilla Link	2644
Resolution	INVALID
Resolved on	Oct 26, 2008 19:17
Version	trunk
OS	Linux
Attachments	testcase; the part that gets miscompiled, driver for the testcase; used to generate 'x.s' in the snippet
Reporter	LLVM Bugzilla Contributor

Extended Description

I have a miscompile:

$ opt -loop-rotate -indvars c.bc | llc -f -o x2.s
nlewycky@ducttape:/local$ gcc x.s x2.s -o x -lm
nlewycky@ducttape:/local$ ./x
Hilbert Slice. Test case 1 of size 120.
One-Norm(A) ---------- 1.833333e+00.
Segmentation fault

Without the 'opt' phase, the program runs correctly. This is a bugpoint reduction of sgefa.

I should mention that opt -loop-rotate | opt -indvars appears to produce different output (it's hard to spot amongst the variable renamings, but it looks like a GEP is missing or in a different spot).

[llvmbot]

Nick,

What are the exact steps to reproduce this bug ? Thanks.

[llvmbot]

Hi Devang,

On Linux it looks like this:

$ opt -loop-rotate -indvars c.bc | llc -f -o c.s
$ llc bugpoint-tonotoptimize.bc -f -o d.s
$ gcc c.s d.s -o sgefa
$ gcc c.s d.s -o sgefa -lm
$ ./sgefa
Hilbert Slice. Test case 1 of size 120.
One-Norm(A) ---------- 1.833333e+00.
Segmentation fault

but I wouldn't be surprised if it didn't work on OSX because of llvm-gcc baked-in headers and what-not.

If you want to go back to the original testcase, visit MultiSource/Applications/sgefa, and run:

bugpoint Output/sgefa.noopt-llvm.bc -mem2reg -instcombine -simplifycfg -loop-rotate -indvars -append-exit-code -rel-tolerance 0.0001 -Xlinker=-lm -input=/dev/null -output=Output/sgefa.out-nat -timeout=500 --tool-args --args --

That should do it!

[lattner]

Still an issue?

[nlewycky]

Nope.