'Can't simplify this node' when building ppc64_defconfig Linux kernel

[nathanchance]

Bugzilla Link	45301
Resolution	FIXED
Resolved on	Apr 14, 2020 20:18
Version	trunk
OS	Windows NT
Blocks	#44654
CC	@topperc,@nickdesaulniers,@nemanjai,@tstellar
Fixed by commit(s)	4821411 321d929

Extended Description

When building the powerpc64 Linux kernel (ppc64_defconfig) with a build of LLVM with assertions enabled:

$ curl -LSs https://git.kernel.org/torvalds/t/linux-5.6-rc7.tar.gz | tar xzf -

$ cd linux-5.6-rc7

$ make -j$(nproc) -s ARCH=powerpc CC=clang CROSS_COMPILE=powerpc64-linux-gnu- O=out/ppc64 distclean defconfig drivers/net/ethernet/emulex/benet/be_cmds.o
Can't simplify this node
UNREACHABLE executed at /home/nathan/cbl/git/tc-build-master/llvm-project/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp:809!
Stack dump:
0. Program arguments: /home/nathan/cbl/git/tc-build-master/build/llvm/stage1/bin/clang-10 -cc1 -triple powerpc64-unknown-linux-gnu -S -disable-free -main-file-name be_cmds.c -mrelocation-model static -mthread-model posix -fno-delete-null-pointer-checks -mllvm -warn-stack-size=2048 -mframe-pointer=all -relaxed-aliasing -fmath-errno -masm-verbose -no-integrated-as -mconstructor-aliases -fuse-init-array -mcode-model large -target-cpu pwr5 -target-feature -altivec -target-feature -vsx -target-feature -spe -target-feature -hard-float -msoft-float -mfloat-abi soft -target-abi elfv1 -dwarf-column-info -debugger-tuning=gdb -coverage-notes-file /tmp/tmp.ioF70h70K2/linux-5.6-rc7/out/ppc64/drivers/net/ethernet/emulex/benet/be_cmds.gcno -nostdsysteminc -nobuiltininc -resource-dir /home/nathan/cbl/git/tc-build-master/build/llvm/stage1/lib/clang/10.0.0 -dependency-file drivers/net/ethernet/emulex/benet/.be_cmds.o.d -MT drivers/net/ethernet/emulex/benet/be_cmds.o -sys-header-deps -isystem /home/nathan/cbl/git/tc-build-master/build/llvm/stage1/lib/clang/10.0.0/include -include /tmp/tmp.ioF70h70K2/linux-5.6-rc7/include/linux/kconfig.h -include /tmp/tmp.ioF70h70K2/linux-5.6-rc7/include/linux/compiler_types.h -I /tmp/tmp.ioF70h70K2/linux-5.6-rc7/arch/powerpc/include -I ./arch/powerpc/include/generated -I /tmp/tmp.ioF70h70K2/linux-5.6-rc7/include -I ./include -I /tmp/tmp.ioF70h70K2/linux-5.6-rc7/arch/powerpc/include/uapi -I ./arch/powerpc/include/generated/uapi -I /tmp/tmp.ioF70h70K2/linux-5.6-rc7/include/uapi -I ./include/generated/uapi -D KERNEL -I /tmp/tmp.ioF70h70K2/linux-5.6-rc7/arch/powerpc -D HAVE_AS_ATHIGH=1 -D _TASK_CPU=300 -I /tmp/tmp.ioF70h70K2/linux-5.6-rc7/drivers/net/ethernet/emulex/benet -I ./drivers/net/ethernet/emulex/benet -D MODULE -D KBUILD_BASENAME="be_cmds" -D KBUILD_MODNAME="be2net" -O2 -Wall -Wundef -Werror=strict-prototypes -Wno-trigraphs -Werror=implicit-function-declaration -Werror=implicit-int -Wno-format-security -Werror=unknown-warning-option -Wno-address-of-packed-member -Wno-format-invalid-specifier -Wno-gnu -Wno-tautological-compare -Wno-unused-const-variable -Wdeclaration-after-statement -Wvla -Wno-pointer-sign -Werror=date-time -Werror=incompatible-pointer-types -Wno-initializer-overrides -Wno-format -Wno-sign-compare -Wno-format-zero-length -std=gnu89 -fno-dwarf-directory-asm -fdebug-compilation-dir /tmp/tmp.ioF70h70K2/linux-5.6-rc7/out/ppc64 -ferror-limit 19 -fmessage-length 0 -pg -fwrapv -fno-signed-char -fwchar-type=short -fno-signed-wchar -fobjc-runtime=gcc -fno-common -fdiagnostics-show-option -fcolor-diagnostics -vectorize-loops -vectorize-slp -o /tmp/be_cmds-d1737c.s -x c /tmp/tmp.ioF70h70K2/linux-5.6-rc7/drivers/net/ethernet/emulex/benet/be_cmds.c

1.  <eof> parser at end of file
   

2.  Code generation
   

3.  Running pass 'Function Pass Manager' on module '/tmp/tmp.ioF70h70K2/linux-5.6-rc7/drivers/net/ethernet/emulex/benet/be_cmds.c'.
   

4.  Running pass 'PowerPC DAG->DAG Pattern Instruction Selection' on function '@be_cmd_rss_config'
   

#​0 0x00000000025383b4 PrintStackTraceSignalHandler(void*) (/home/nathan/cbl/git/tc-build-master/build/llvm/stage1/bin/clang-10+0x25383b4)
#​1 0x00000000025362ce llvm::sys::RunSignalHandlers() (/home/nathan/cbl/git/tc-build-master/build/llvm/stage1/bin/clang-10+0x25362ce)
#​2 0x00000000025387c5 SignalHandler(int) (/home/nathan/cbl/git/tc-build-master/build/llvm/stage1/bin/clang-10+0x25387c5)
#​3 0x00007f84b246c890 __restore_rt (/lib/x86_64-linux-gnu/libpthread.so.0+0x12890)
#​4 0x00007f84b113fe97 raise (/lib/x86_64-linux-gnu/libc.so.6+0x3ee97)
#​5 0x00007f84b1141801 abort (/lib/x86_64-linux-gnu/libc.so.6+0x40801)
#​6 0x00000000024e2961 (/home/nathan/cbl/git/tc-build-master/build/llvm/stage1/bin/clang-10+0x24e2961)
#​7 0x00000000032b5371 llvm::TargetLowering::SimplifyDemandedBits(llvm::SDValue, llvm::APInt const&, llvm::APInt const&, llvm::KnownBits&, llvm::TargetLowering::TargetLoweringOpt&, unsigned int, bool) const (/home/nathan/cbl/git/tc-build-master/build/llvm/stage1/bin/clang-10+0x32b5371)
#​8 0x00000000032ab6fd llvm::TargetLowering::SimplifyDemandedBits(llvm::SDValue, llvm::APInt const&, llvm::APInt const&, llvm::KnownBits&, llvm::TargetLowering::TargetLoweringOpt&, unsigned int, bool) const (/home/nathan/cbl/git/tc-build-master/build/llvm/stage1/bin/clang-10+0x32ab6fd)
#​9 0x00000000030e936b (anonymous namespace)::DAGCombiner::SimplifyDemandedBits(llvm::SDValue, llvm::APInt const&) (/home/nathan/cbl/git/tc-build-master/build/llvm/stage1/bin/clang-10+0x30e936b)
#​10 0x00000000030e537a (anonymous namespace)::DAGCombiner::visitADDLike(llvm::SDNode*) (/home/nathan/cbl/git/tc-build-master/build/llvm/stage1/bin/clang-10+0x30e537a)
#​11 0x0000000003095244 (anonymous namespace)::DAGCombiner::visit(llvm::SDNode*) (/home/nathan/cbl/git/tc-build-master/build/llvm/stage1/bin/clang-10+0x3095244)
#​12 0x000000000308ffdc (anonymous namespace)::DAGCombiner::combine(llvm::SDNode*) (/home/nathan/cbl/git/tc-build-master/build/llvm/stage1/bin/clang-10+0x308ffdc)
#​13 0x000000000308db26 llvm::SelectionDAG::Combine(llvm::CombineLevel, llvm::AAResults*, llvm::CodeGenOpt::Level) (/home/nathan/cbl/git/tc-build-master/build/llvm/stage1/bin/clang-10+0x308db26)
#​14 0x00000000031f259a llvm::SelectionDAGISel::CodeGenAndEmitDAG() (/home/nathan/cbl/git/tc-build-master/build/llvm/stage1/bin/clang-10+0x31f259a)
#​15 0x00000000031f0502 llvm::SelectionDAGISel::SelectAllBasicBlocks(llvm::Function const&) (/home/nathan/cbl/git/tc-build-master/build/llvm/stage1/bin/clang-10+0x31f0502)
#​16 0x00000000031ece06 llvm::SelectionDAGISel::runOnMachineFunction(llvm::MachineFunction&) (/home/nathan/cbl/git/tc-build-master/build/llvm/stage1/bin/clang-10+0x31ece06)
#​17 0x000000000162e1a1 (anonymous namespace)::PPCDAGToDAGISel::runOnMachineFunction(llvm::MachineFunction&) (/home/nathan/cbl/git/tc-build-master/build/llvm/stage1/bin/clang-10+0x162e1a1)
#​18 0x0000000001c1867e llvm::MachineFunctionPass::runOnFunction(llvm::Function&) (/home/nathan/cbl/git/tc-build-master/build/llvm/stage1/bin/clang-10+0x1c1867e)
#​19 0x0000000001f9af89 llvm::FPPassManager::runOnFunction(llvm::Function&) (/home/nathan/cbl/git/tc-build-master/build/llvm/stage1/bin/clang-10+0x1f9af89)
#​20 0x0000000001f9b3c8 llvm::FPPassManager::runOnModule(llvm::Module&) (/home/nathan/cbl/git/tc-build-master/build/llvm/stage1/bin/clang-10+0x1f9b3c8)
#​21 0x0000000001f9baf4 llvm::legacy::PassManagerImpl::run(llvm::Module&) (/home/nathan/cbl/git/tc-build-master/build/llvm/stage1/bin/clang-10+0x1f9baf4)
#​22 0x00000000026fc25e clang::EmitBackendOutput(clang::DiagnosticsEngine&, clang::HeaderSearchOptions const&, clang::CodeGenOptions const&, clang::TargetOptions const&, clang::LangOptions const&, llvm::DataLayout const&, llvm::Module*, clang::BackendAction, std::unique_ptr<llvm::raw_pwrite_stream, std::default_deletellvm::raw_pwrite_stream >) (/home/nathan/cbl/git/tc-build-master/build/llvm/stage1/bin/clang-10+0x26fc25e)
#​23 0x0000000002e1c1ca clang::BackendConsumer::HandleTranslationUnit(clang::ASTContext&) (/home/nathan/cbl/git/tc-build-master/build/llvm/stage1/bin/clang-10+0x2e1c1ca)
#​24 0x00000000034ebeb3 clang::ParseAST(clang::Sema&, bool, bool) (/home/nathan/cbl/git/tc-build-master/build/llvm/stage1/bin/clang-10+0x34ebeb3)
#​25 0x0000000002d88be0 clang::FrontendAction::Execute() (/home/nathan/cbl/git/tc-build-master/build/llvm/stage1/bin/clang-10+0x2d88be0)
#​26 0x0000000002cf32b2 clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/home/nathan/cbl/git/tc-build-master/build/llvm/stage1/bin/clang-10+0x2cf32b2)
#​27 0x0000000002e16cf4 clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/home/nathan/cbl/git/tc-build-master/build/llvm/stage1/bin/clang-10+0x2e16cf4)
#​28 0x000000000159dac9 cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/home/nathan/cbl/git/tc-build-master/build/llvm/stage1/bin/clang-10+0x159dac9)
#​29 0x0000000001599c8a main (/home/nathan/cbl/git/tc-build-master/build/llvm/stage1/bin/clang-10+0x1599c8a)
#​30 0x00007f84b1122b97 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b97)
#​31 0x0000000001598daa _start (/home/nathan/cbl/git/tc-build-master/build/llvm/stage1/bin/clang-10+0x1598daa)
clang-10: error: unable to execute command: Aborted
clang-10: error: clang frontend command failed due to signal (use -v to see invocation)

I bisected this down to 1b7b4b4, which adds the llvm_unreachable that this driver trips over.

creduce spits out:

a(void *b, int c) {
int *d = b;
do {
*d = __builtin_constant_p(0)
? (*d & 255UL) << 24 | (*d & 65280UL) << 8 |
(*d & 16711680UL) >> 8 | (*d & 4278190080) >> 24
: 0;
d++;
c -= 4;
} while (c);
}
struct e {
int f[10]
} g() {
struct e *h = i();
memcpy(h, g, 40);
a(h, sizeof(h->f));
}

Full preprocessed file and interestingness test available at https://github.com/nathanchance/creduce-files/tree/887a2dff5ee05d953b059cf6ac3ead478fa50ee6/ppc64-be_cmds.

[nathanchance]

assigned to @efriedma-quic

[nemanjai]

OK, I see the issue. We break apart a pre-inc load into the use of another load as well as an ADD (to update the pointer). But we have already provided a TargetConstant for the pre-inc load so we hit an UNREACHABLE when trying to combine the new add.
I'll propose a patch soon.

[nemanjai]

Proposed fix: https://reviews.llvm.org/D76778

Please review and test whether it fixes the issue.

[nathanchance]

I can confirm that that fix works. I do not feel qualified enough to review LLVM backend code so I'll defer to others on that.

[nathanchance]

I would like to see the fix for this in 10.0.1 since a continuous integration setup for the Linux kernel caught this in the wild (https://groups.google.com/d/msg/clang-built-linux/kLFQXQS6D94/-VCXkmhtBQAJ) so adding this as a blocker to that issue. Feel free to remove if you disagree.

[nickdesaulniers]

fixed: https://reviews.llvm.org/rG482141134729237072cb94248381dab96ce34374

[nathanchance]

Reopening to properly track for llvm-10.0.1.

[tstellar]

Hi Eli,

Is this OK to backport?

https://github.com/tstellar/llvm-project/pull/75/files

[efriedma-quic]

Yes, that's safe to backport.

[tstellar]

Merged: 321d929

[tstellar]

mentioned in issue #44654