Compiling MiBench to MIPS

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#1

Hi,

I’m trying to compile the basicmath benchmark from the MiBench suite to the MIPS target. However, when I call llc with the linked llvm bitcode, the compilation gives an error apparently related to some unsupported feature. The same error occurs when I select -march=arm, but it works for X86. In details:

Commands I used to compile basicmath:

clang -static -O3 basicmath_small.c rad2deg.c cubic.c isqrt.c -c -emit-llvm
llvm-link basicmath_small.bc rad2deg.bc cubic.bc isqrt.bc -o basicmath.bc
llc basicmath.bc -march=mipsel -relocation-model=static -o basicmath

The error is:

llc: /home/ronaldo/llvm/include/llvm/Target/TargetLowering.h:302: virtual const llvm::TargetRegisterClass* llvm::TargetLoweringBase::getRegClassFor(llvm::MVT) const: Assertion `RC && “This value type is not natively supported!”’ failed.
0 llc 0x0000000001557f2d llvm::sys::PrintStackTrace(_IO_FILE*) + 38
1 llc 0x00000000015581aa
2 llc 0x0000000001557b50
3 libpthread.so.0 0x00007f2d54c26340
4 libc.so.6 0x00007f2d53e62f79 gsignal + 57
5 libc.so.6 0x00007f2d53e66388 abort + 328
6 libc.so.6 0x00007f2d53e5be36
7 libc.so.6 0x00007f2d53e5bee2
8 llc 0x00000000009be707
9 llc 0x0000000000cfed54 llvm::FunctionLoweringInfo::CreateReg(llvm::MVT) + 64
10 llc 0x0000000000cfeebd llvm::FunctionLoweringInfo::CreateRegs(llvm::Type*) + 337
11 llc 0x0000000000cf33fa
12 llc 0x0000000000cfe4cb llvm::FunctionLoweringInfo::set(llvm::Function const&, llvm::MachineFunction&, llvm::SelectionDAG*) + 2033
13 llc 0x0000000000dadb1d llvm::SelectionDAGISel::runOnMachineFunction(llvm::MachineFunction&) + 921
14 llc 0x0000000000b01037 llvm::MipsDAGToDAGISel::runOnMachineFunction(llvm::MachineFunction&) + 35
15 llc 0x0000000000b2a9a1 llvm::MipsSEDAGToDAGISel::runOnMachineFunction(llvm::MachineFunction&) + 65
16 llc 0x0000000000fcd6ed llvm::MachineFunctionPass::runOnFunction(llvm::Function&) + 95
17 llc 0x00000000014d0825 llvm::FPPassManager::runOnFunction(llvm::Function&) + 291
18 llc 0x00000000014d09d0 llvm::FPPassManager::runOnModule(llvm::Module&) + 84
19 llc 0x00000000014d0cee
20 llc 0x00000000014d13b8 llvm::legacy::PassManagerImpl::run(llvm::Module&) + 244
21 llc 0x00000000014d15c3 llvm::legacy::PassManager::run(llvm::Module&) + 39
22 llc 0x00000000008c4893
23 llc 0x00000000008c3ac3 main + 237
24 libc.so.6 0x00007f2d53e4dec5 __libc_start_main + 245
25 llc 0x00000000008c1589
Stack dump:
0. Program arguments: …/…/…/sw/llc basicmath.bc -march=mipsel -relocation-model=static -o basicmath

  1. Running pass ‘Function Pass Manager’ on module ‘basicmath.bc’.
  2. Running pass ‘MIPS DAG->DAG Pattern Instruction Selection’ on function ‘@SolveCubic’
    Aborted (core dumped)

Am I missing something in the compilation?

#2

Hi Ronaldo,

clang -static -O3 basicmath_small.c rad2deg.c cubic.c isqrt.c -c -emit-llvm
llvm-link basicmath_small.bc rad2deg.bc cubic.bc isqrt.bc -o basicmath.bc
llc basicmath.bc -march=mipsel -relocation-model=static -o basicmath

My best guess is that the LLVM IR created on line 1 is actually for
x86-64 (generated by a Clang targeting x86-64, having included x86-64
headers and so on). When you override the output target on the third
line, you would end up feeding the MIPS backend IR that it's not
equipped to deal with. Clang's output *does* depend on what it's
targeting.

If so, you need to create a proper cross-development environment for
MIPS (binutils, libc, headers, ...) and point clang at it in the first
line (via -target and -sysroot at least, possibly other options too;
getting the driver to work properly can be a tricky business. Use "-v"
to get it to tell you more about what it's trying to do). Then the
later lines should work fine (though you won't need the -march option
for llc).

Cheers.

Tim.

P.S. The backends probably shouldn't crash regardless, but the reality
is that they're adapted to the kind of IR Clang produces when it knows
it's targeting them and other configurations are much less
well-tested. Since the alternative is successfully generating wrong
code, it's not much of a priority for me at least.

#3

Thanks Tim, I was not aware of that issue with clang. I could compile with:

clang --target=mips-linux-gnu --sysroot=/home/ronaldo/CodeSourcery/Sourcery_CodeBench_Lite_for_MIPS_GNU_Linux -static -O3 basicmath_small.c rad2deg.c cubic.c isqrt.c -c -emit-llvm

I already had the MIPS toolchain installed.

#4

Hi,

Thanks Tim, I was not aware of that issue with clang. I could compile with:

clang --target=mips-linux-gnu
--sysroot=/home/ronaldo/CodeSourcery/Sourcery_CodeBench_Lite_for_MIPS_GNU_Linux
-static -O3 basicmath_small.c rad2deg.c cubic.c isqrt.c -c -emit-llvm

I already had the MIPS toolchain installed.

BTW if Sourcery_CodeBench_Lite_for_MIPS_GNU_Linux is a regular
CodeSourcery toolchain installation directory i.e. it contains folders
like "bin", "lib", "mips-linux-gnu" etc, I recommend to do not use the
'--sysroot' option and invoke the clang as:

% clang --gcc-toolchain=/home/ronaldo/CodeSourcery/Sourcery_CodeBench_Lite_for_MIPS_GNU_Linux
--target=mips-linux-gnu ...

In fact this toolchain contains multiple "sysroot's" for various
combination of command line options -EL/-BE, mips32/mips32r2 etc. The
"--gcc-toolchain" option allows the driver correctly select an
appropriate "sysroot" for specified arguments.