LLVM miscompiles a function from Wine

[llvmbot]

Bugzilla Link	8561
Resolution	INVALID
Resolved on	Oct 14, 2012 15:28
Version	trunk
OS	All
Blocks	llvm/llvm-bugzilla-archive#10638
Attachments	LLVM IR of miscompiled function from Wine
Reporter	LLVM Bugzilla Contributor
CC	@asl

Extended Description

Now that #8790 is fixed (thanks, Chris!), I took a stab at building Wine with Clang at -O2. It builds successfully, but unfortunately, the resulting Wine segfaults on start-up. This happens before Wine installs its own signal handlers, so the OS picks it up and produces a backtrace. The backtrace pointed to the "reserve_area" function.

I've isolated this function and compiled it to LLVM IR. I don't know where or why this is happening, but this is preventing Wine from being usable when compiled at -O2.

From looking at the source, this function is a recursive function, so that could have something to do with it.

[lattner]

Hi Charles. I'd like to investigate this, but the testcase is invalid.

$ llc mmap.ll -o -
llc: mmap.ll:64:1: error: expected instruction opcode
}
^

after fixing that:

$ llc mmap.ll -o -
llc: mmap.ll:38:13: error: use of undefined value '@wine_mmap_add_reserved_area'
call void @​wine_mmap_add_reserved_area(i8* %addr, i32 %3)
^

[llvmbot]

LLVM IR of entire source file from Wine
All right, here's the IR for the entire source file. I checked out that llc works on it.

[llvmbot]

The problem is still present in trunk, by the way.

[llvmbot]

LLVM IR of miscompiled function from Wine
That last attachment was a bit much. It had debug info and everything in it.

Here's one without any debug info, and only the stuff needed to compile @​reserve_area. That should be a little more manageable. I ran this through llc as well just to make sure it wasn't malformed.

[llvmbot]

Still present in trunk.

I compiled Wine with Clang at -O1 just now (with Clang trunk), and it runs just fine (i.e. no stack overflow, no segfault). The problem must be one of the optimization passes that gets enabled at -O2.

[llvmbot]

Reduced LLVM IR of miscompiled reserve_area()
OK, I've run bugpoint on a modified version of the testcase, and I've produced this reduced testcase. Hope that helps.

[llvmbot]

Seems to work at:
git-svn-id: http://llvm.org/svn/llvm-project/llvm/trunk@150433 91177308-0d34-0410-b5e6-96231b3b80d8

and wine-1.4-rc3-23-gd548af4.

There's a crash on first start of wine, that's bug 9844. After that though, at least basic stuff works. Charles, please confirm.

[llvmbot]

Yeah, it works. Resolving old bug that turns out not to be a bug in LLVM at all. (Sorry it took so long to get back on this...)