similar to: [LLVMdev] request for help writing a register allocator

Hi Susan, You may find the PBQP allocator implementation useful as a reference to what's involved in adding a new allocator to LLVM. It's located in lib/CodeGen/RegAllocPBQP.cpp, with supporting files in the lib/CodeGen/ PBQP directory. I'm no expert on the LLVM register allocation interfaces, so I'll defer to those who are regarding the specifics of your questions. -Jim

Hi Susan, > You may find the PBQP allocator implementation useful as a reference > to what's involved in adding a new allocator to LLVM. It's located in > lib/CodeGen/RegAllocPBQP.cpp, with supporting files in the lib/CodeGen/ > PBQP directory. > Yes - as far as working allocators go PBQP is pretty simple. If you're just interested in LLVM API details you can focus on

Hey all, I've found a bug in either the PBQP register allocator or in VirtRegRewriter. I'm observing this assertion in VirtRegRewriter::rewrite() fail: unsigned VirtReg = MO.getReg(); unsigned PhysReg = VRM->getPhys(VirtReg); ... assert(!MRI->isReserved(PhysReg) && "Reserved register assignment"); Indeed there is a case where

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,

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

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

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

My tst.bc is attached. I had to use ssh to copy it from my office machine to my home laptop. In case that corrupts it, I also put a copy here: http://pages.cs.wisc.edu/~horwitz/LANG/tst.bc I created the file like this: clang -emit-llvm -O0 -c tst.c -o tst.bc opt -mem2reg tst.bc > tst.mem2reg mv tst.mem2reg tst.bc Susan On 11/4/2012 3:27 PM, Lang Hames wrote: > Hi Susan, >

Lang - Your version does NOT work for me (i.e., I still get an error from the assembler when I run your code on my tst.c) unless I force compilation and assembly for a 32-bit X86 machine: llc -march=x86 -regalloc=gc tst.bc gcc -m32 tst.s My machine is a 64-bit machine. Maybe you are working with a different architecture and that's why it worked for you? I would be happy if the

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

Hi Susan, With your bitcode file I am now able to reproduce the issue you're seeing. It looks like this is a problem with the naive rewriting from virtregs to physregs. It appears that the subreg field of physreg operands is ignored post-register allocation. In your testcase %vreg11:sub32 is being rewritten to RBX:sub32, but the :sub32 part is being quietly dropped when the assembly is

Hi Susan, Without debugging symbols I can't make much out of that stack trace I'm afraid. I've attached my modified version of Gcra.cpp. I built llvm 3.1 by dropping this file into lib/CodeGen, and adding references to createGcra to include/lib/CodeGen/Passes.h and include/lib/CodeGen/LinkAllCodeGenComponents.h. (If you search for createRegAllocPBQP you'll see where to add the

Hi Lang, I looked more into one of the problems I'm now having, and I've attached 3 files: Gcra.cpp is like your version except that for two specific vregs it uses hard-coded pregs instead of the first in the corresponding class. bug1.c is an input that causes the failed assertion for me. If I use the non-debug version of LLVM-3.1 I instead get assembler errors like this: Error:

Hi Susan, I tested the version of Gcra.cpp that I sent you on x86-64 systems running MacOS 10.8 and Ubuntu 12.04 (Linux 3.2.0). Could you send me the bitcode file you're compiling? Different bitcodes (due to different clang versions or applied optimizations) could account for the different results we're seeing. For reference I've attached the *.ll file that I have tested with, which

Hi Susan, It looks like the bitcode you have attached is corrupted. You should make sure to attach it as a binary file. Alternatively you can attach the LLVM assembly as text. You can generate an assembly file from bitcode with: llvm-dis -o <asm file> <bitcode> Regards, Lang. On Fri, Nov 9, 2012 at 11:15 AM, Susan Horwitz <horwitz at cs.wisc.edu> wrote: > Thanks Lang,

Hi Susan, The problem is that the allocator is re-using the 'preg', which is calculated for an operand that may have a subreg index, for loads and stores to a stack-slot. The stack slot always has the same width as vreg (which is the right behavior), but for operands with subreg indexes, 'preg''s class will be different from 'vreg', in which case you get the mismatched

Sorry about that. I created the assembly file and attached it (as math.txt). Susan On 11/11/2012 12:41 AM, Lang Hames wrote: > Hi Susan, > > It looks like the bitcode you have attached is corrupted. You should > make sure to attach it as a binary file. Alternatively you can attach > the LLVM assembly as text. You can generate an assembly file from > bitcode with: > >

Hi Susan, In x86-64 the REX prefix must be used to access an extended register (r8-r15 and their aliases), but cannot be used when accessing the high byte of the ABCD regs (AH, BH, CH, DH). In your test case you have hardcoded %vreg1 to R8B, and %vreg15 to AH, and the test case contains a copy between these registers. The copy simultaneously must have a REX prefix, and cannot have a REX prefix,

Hi Susan, Sorry for the delayed response. Thanks for the test cases - I'm looking in to this now. - Lang. On Mon, Nov 5, 2012 at 2:58 PM, Susan Horwitz <horwitz at cs.wisc.edu> wrote: > Hi Lang, > > I looked more into one of the problems I'm now having, and I've attached 3 > files: > > Gcra.cpp is like your version except that for two specific vregs it uses

Lang - Your fix does prevent the assembler errors, but it doesn't seem to produce correct assembly. I created a slightly modified version that, for each instruction that includes a vreg, adds a check that the preg selected is not already in that instruction. I've attached that version. I think that this version of Gcra.cpp should produce correct assembler, since it's allocating