UNREACHABLE executed at llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp:5726!

[pkubaj]

Bugzilla Link	45579
Resolution	FIXED
Resolved on	Jun 26, 2020 13:51
Version	10.0
OS	FreeBSD
Blocks	#44654
CC	@adalava,@topperc,@DimitryAndric,@RKSimon,@tstellar
Fixed by commit(s)	3906ae3 76ceebb

Extended Description

FreeBSD head, LLVM 10.0.0, powerpc, powerpcspe and powerpc64 architectures

Reduced test case:
double a(double);
template class b;
template <typename c, typename i> void operator==(i &, c);
template <> class b {
public:
b(double = 0.0);
};
b d;
double e;
template <class f, class g> void h(f m, g) {
b j;
m == d;
double k = a(0);
j = e / 2 + (m - .5) * k - m;
}
double l() { h(.5, 0); }

Compile with:
/usr/bin/c++ -cc1 -triple powerpc-unknown-freebsd13.0 -emit-obj -ffast-math -O1 -fgnuc-version=4.2.1 Lgamma-106832.cpp

Result:
Unknown code
UNREACHABLE executed at /usr/src/contrib/llvm-project/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp:5726!
Stack dump:
0. Program arguments: /usr/bin/c++ -cc1 -triple powerpc-unknown-freebsd13.0 -emit-obj -ffast-math -O1 -fgnuc-version=4.2.1 Lgamma-106832.cpp

1.  <eof> parser at end of file
   

2.  Code generation
   

3.  Running pass 'Function Pass Manager' on module 'Lgamma-106832.cpp'.
   

4.  Running pass 'PowerPC DAG->DAG Pattern Instruction Selection' on function '@_Z1hIdiEvT_T0_'
   

#​0 0x0000000013bada64 PrintStackTrace /usr/src/contrib/llvm-project/llvm/lib/Support/Unix/Signals.inc:564:13
#​1 0x0000000013bab12c RunSignalHandlers /usr/src/contrib/llvm-project/llvm/lib/Support/Signals.cpp:67:5
#​2 0x0000000013bae86c SignalHandler /usr/src/contrib/llvm-project/llvm/lib/Support/Unix/Signals.inc:0:3
#​3 0x0000000815734748 handle_signal /usr/src/lib/libthr/thread/thr_sig.c:303:3
Abort trap (core dumped)

[pkubaj]

assigned to @rotateright

[adalava]

This is a LLVM 10 regression. Both LLVM 9.0.1 and trunk @ 3e31569 wont crash, givis this warning instead:

warning: non-void function does not return a value
double l() { h(.5, 0); }

[pkubaj]

Tested to happen also on 10.0.1-rc1-0-gf79cd71e145.

[adalava]

It builds with optimization level -O0. Crashes with O1, O2 or O3.

[tstellar]

It looks like this was fixed in trunk by 3906ae3.

Sanjay, what do you think about backporting this?

https://github.com/tstellar/llvm-project/pull/200/files

[rotateright]

It looks like this was fixed in trunk by
3906ae3.

Sanjay, what do you think about backporting this?

https://github.com/tstellar/llvm-project/pull/200/files

That was: https://reviews.llvm.org/D75501

I think that was safer than the hack it replaced, but we didn't solve the problem completely until:
https://reviews.llvm.org/D77319 / https://reviews.llvm.org/rG2b59e9f1bdd8d0f8a315f9ddba2cdc87a3e682fb
...but that's probably too much for a bug-fix release?

cc'ing Simon, Qing Shan (Steven), Craig.

[tstellar]

I think since it's late in the release cycle, we'll just take 3906ae3. That other patch is pretty large.

[tstellar]

Merged: 76ceebb