[LLVMdev] problem trying to write an LLVM register-allocation pass
Susan Horwitz
horwitz at cs.wisc.edu
Thu Nov 1 15:13:20 PDT 2012
I still get a coredump:
0 libLLVM-3.1.so 0x00007f0158a4e67f
1 libLLVM-3.1.so 0x00007f0158a500ca
2 libpthread.so.0 0x0000003a86c0f500
3 libLLVM-3.1.so 0x00007f01583c346c
4 libLLVM-3.1.so 0x00007f0158546349
llvm::FPPassManager::runOnFunction(llvm::Function&) + 521
5 libLLVM-3.1.so 0x00007f01585463e3
llvm::FPPassManager::runOnModule(llvm::Module&) + 51
6 libLLVM-3.1.so 0x00007f0158545fae
llvm::MPPassManager::runOnModule(llvm::Module&) + 462
7 libLLVM-3.1.so 0x00007f01585460bd
llvm::PassManagerImpl::run(llvm::Module&) + 125
8 llc 0x000000000040b012 main + 5218
9 libc.so.6 0x0000003a8601ecdd __libc_start_main + 253
10 llc 0x0000000000407d79
Stack dump:
0. Program arguments: llc -load Debug/lib/P4.so -regalloc=gc tst.bc
1. Running pass 'Function Pass Manager' on module 'tst.bc'.
2. Running pass 'Machine Loop Invariant Code Motion' on function
'@main'
make: *** [tst.reg] Segmentation fault (core dumped)
On 11/01/2012 04:59 PM, Lang Hames wrote:
> Hi Susan,
>
> Sorry - I had missed that you're using llvm-3.1, rather than the
> development branch. We encourage people to live on top-of-tree - it's
> well tested, easier for active developers to offer help with, and
> keeping up with incremental changes is often easier than porting between
> stable versions.
>
> It also sounds like you were building a Release version of LLVM. That
> will not have any asserts enabled (though it will have some other
> diagnostics). You will probably want to work with a Debug+Asserts
> version (<src>/configure --disable-optimized --enable-assertions) while
> you're developing your allocator and watch for any asserts that trigger.
>
> In your case the Assertion that is triggering in PEI indicates that the
> MachineRegisterInfo object still contained some virtregs post
> register-allocation. You need to call MRI->clearVirtRegs() at the end of
> your allocator.
>
> Hope this helps!
>
> Cheers,
> Lang.
>
> On Thu, Nov 1, 2012 at 2:41 PM, Susan Horwitz <horwitz at cs.wisc.edu
> <mailto:horwitz at cs.wisc.edu>> wrote:
>
> Hi again Lang,
>
> I decided to try the approach you proposed to see whether it makes
> the assembly-code problem go away. Again, I tried a very simple
> register allocator (attached) that just calls vrm.assignVirt2Phys
> for every vreg in each function, mapping the vreg to the first preg
> in the register class. I tried two versions: one maps *every* vreg,
> and the other only maps those for which MRI->reg_empty(vreg) returns
> false. In both cases I get a core dump somewhere after my
> reg-allocation pass has run (when I use the "tst.c" file that I sent
> last time as input).
>
> Note also that there is no VirtRegMap.h in the "include" directory
> of my installed llvm-3.1. I had to copy that file from the source
> directory. That seems suspicious.
>
> Any thoughts?
>
> Thanks!
>
> Susan
>
>
> On 10/31/2012 07:51 PM, Lang Hames wrote:
>
> Hi Susan,
>
> I'm having trouble reproducing that error on my end, but I think the
> problem is probably that you're not using the VirtRegRewriter
> infrastructure. What your allocator needs to do is populate the
> virtual
> register mapping (VirtRegMap pass) with your allocation, rather than
> rewriting the registers directly through MachineRegisterInfo.
>
> Have your allocator require and preserve the VirtRegMap pass,
> then in
> your runOnMachineFunction pass grab a reference to the pass with:
>
> VirtRegMap &vrm = getAnalysis<VirtRegMap>();
>
> You can then describe your register allocations with:
>
> vrm.assignVirt2Phys(<virtreg>, <physreg>)
>
> The VirtRegRewriter pass (in VirtRegMap.cpp) will run after your
> allocator and apply the mapping that you described in the
> VirtRegMap.
>
> I hope this helps. Let me know if it doesn't fix your issue.
>
> Cheers,
> Lang.
>
> On Wed, Oct 31, 2012 at 3:54 PM, Susan Horwitz
> <horwitz at cs.wisc.edu <mailto:horwitz at cs.wisc.edu>
> <mailto:horwitz at cs.wisc.edu <mailto:horwitz at cs.wisc.edu>>> wrote:
>
> Thanks Lang!
>
> Here's another question: I'm trying to process this input:
>
> int main() {
> return 0;
> }
>
> but I'm getting an error
> Assertion `!Fn.getRegInfo(). getNumVirtRegs() &&
> "Regalloc must
>
> assign all vregs"' failed.
>
> At the start of runOnMachineFunction I call Fn.getRegInfo().
> getNumVirtRegs();
> and find that there is 1 virtual register. However,
> MRI->reg_empty(vreg)
> tells me that it is not used or defined. So my
> register-allocation
> code never sees it, and thus can't allocate a preg for it.
> I tried
> using MRI->replaceRegWith(vreg, preg);
> (where preg is available to vreg's register class) but that
> didn't
> work. When I look, the number of vregs in the function is
> still 1.
>
> Can you help with this?
>
> Thanks again!
>
> Susan
>
>
> On 10/31/2012 04:55 PM, Lang Hames wrote:
>
> Hi Susan,
>
> The meaning of "addRequired(X)" is that your pass needs
> X to be
> run, and
> for X to be preserved by all passes that run after X
> and before your
> pass. The PHIElemination and TwoAddressInstruction
> passes do not
> preserve each other, hence there's no way for the pass
> manager to
> schedule them for you if you addRequire(...) them.
>
> The trick is that CodeGen will schedule both of these
> passes to
> be run
> before _any_ register allocation pass (see Passes.cpp),
> so you
> needn't
> require them explicitly - you can just assume they have
> been
> run. If you
> just remove those lines from your getAnalysisUsage
> method your pass
> should now run as you expect.
>
> Cheers,
> Lang.
>
> On Wed, Oct 31, 2012 at 1:46 PM, Susan Horwitz
> <horwitz at cs.wisc.edu <mailto:horwitz at cs.wisc.edu>
> <mailto:horwitz at cs.wisc.edu <mailto:horwitz at cs.wisc.edu>>
> <mailto:horwitz at cs.wisc.edu <mailto:horwitz at cs.wisc.edu>
> <mailto:horwitz at cs.wisc.edu <mailto:horwitz at cs.wisc.edu>>>> wrote:
>
> I'm trying to write a MachineFunctionPass to do
> register
> allocation.
> I have code that worked with an old version of
> LLVM. It
> does not
> work with llvm-3.1. (or various other versions
> that I've
> tried).
>
> The first problem is that including this line:
>
> AU.addRequiredID(__ TwoAddressInstructionPassID);
>
>
> in method getAnalysisUsage causes a runtime error:
>
> Unable to schedule 'Eliminate PHI nodes for register
> allocation'
> required by 'Unnamed pass: implement
> Pass::getPassName()'
> Unable to schedule pass
> UNREACHABLE executed at ...
>
> I'm invoking the pass like this (given input file
> foo.c):
>
> clang -emit-llvm -O0 -c foo.c -o foo.bc
> opt -mem2reg foo.bc > foo.ssa
> mv foo.ssa foo.bc
> llc -load Debug/lib/P4.so -regalloc=gc foo.bc
>
>
> I've attached my entire file (it's very short).
> Any help
> would be
> much appreciated!
>
> Susan Horwitz
>
> ______________________________ _________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu <mailto:LLVMdev at cs.uiuc.edu>
> <mailto:LLVMdev at cs.uiuc.edu <mailto:LLVMdev at cs.uiuc.edu>>
> <mailto:LLVMdev at cs.uiuc.edu <mailto:LLVMdev at cs.uiuc.edu>
> <mailto:LLVMdev at cs.uiuc.edu <mailto:LLVMdev at cs.uiuc.edu>>>
>
> http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/ mailman/listinfo/llvmdev
> <http://lists.cs.uiuc.edu/__mailman/listinfo/llvmdev
> <http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev>>
>
>
>
>
>
>
More information about the llvm-dev
mailing list