[llvm-dev] Issue with a SetVector of WeakVH-s

[Arnamoy Bhattacharyya via llvm-dev]

Hello;

I was writing code to use WeakVH instead of Instruction*, to get rid
of a dangling pointer error.  I have the following datastructure:

SetVector<WeakVH, SmallVector<WeakVH, 8>> DeadInsts;

But I am seeing the following error while inserting a value into this SetVector:

clang-10: /home/for_upload/llvm-project_1141/llvm/include/llvm/ADT/DenseMap.h:378:
void llvm::DenseMapBase<DerivedT, KeyT, ValueT, KeyInfoT,
BucketT>::moveFromOldBuckets(BucketT*, BucketT*) [with DerivedT =
llvm::DenseMap<llvm::WeakVH, llvm::detail::DenseSetEmpty,
llvm::DenseMapInfo<llvm::WeakVH>,
llvm::detail::DenseSetPair<llvm::WeakVH> >; KeyT = llvm::WeakVH;
ValueT = llvm::detail::DenseSetEmpty; KeyInfoT =
llvm::DenseMapInfo<llvm::WeakVH>; BucketT =
llvm::detail::DenseSetPair<llvm::WeakVH>]: Assertion `!FoundVal &&
"Key already in new map?"' failed.

Stack dump:
0.      Program arguments:
/home/for_upload/llvm-project_1141/install/bin/clang-10 -cc1 -triple
aarch64-unknown-linux-gnu -emit-obj -disable-free -main-file-name
test.c -mrelocation-model static -mthread-model posix -mllvm
-pass-remarks= -mllvm -pass-remarks-missed= -mllvm
-pass-remarks-analysis= -mframe-pointer=non-leaf -fmath-errno
-ffp-contract=fast -fno-rounding-math -masm-verbose
-mconstructor-aliases -target-feature +v8.2a -target-feature +fp-armv8
-target-feature +neon -target-feature +crc -target-feature +crypto
-target-feature +dotprod -target-feature +fp16fml -target-feature +spe
-target-feature +ras -target-feature +lse -target-feature +rdm
-target-feature +complxnum -target-feature +fullfp16 -target-feature
+sha2 -target-feature +aes -target-abi aapcs
-fallow-half-arguments-and-returns -dwarf-column-info
-fno-split-dwarf-inlining -debugger-tuning=gdb -resource-dir
/home/for_upload/llvm-project_1141/install/lib/clang/10.0.1
-internal-isystem /usr/local/include -internal-isystem
/home/for_upload/llvm-project_1141/install/lib/clang/10.0.1/include
-internal-externc-isystem /include -internal-externc-isystem
/usr/include -O3 -w -fdebug-compilation-dir /home/bug/1141
-ferror-limit 19 -fmessage-length 0 -fno-signed-char
-fgnuc-version=4.2.1 -fobjc-runtime=gcc -fdiagnostics-show-option
-vectorize-loops -vectorize-slp -faddrsig -o /tmp/test-523a20.o -x c
test.c
1.      <eof> parser at end of file
2.      Per-module optimization passes
3.      Running pass 'CallGraph Pass Manager' on module 'test.c'.
4.      Running pass 'SROA' on function '@g'

#0 0x0000aaaad333ed40 llvm::sys::PrintStackTrace(llvm::raw_ostream&)
(/home/for_upload/llvm-project_1141/install/bin/clang-10+0x2045d40)
#1 0x0000aaaad333cf08 llvm::sys::RunSignalHandlers()
(/home/for_upload/llvm-project_1141/install/bin/clang-10+0x2043f08)
#2 0x0000aaaad333d6d8 SignalHandler(int)
(/home/for_upload/llvm-project_1141/install/bin/clang-10+0x20446d8)
#3 0x0000ffff805c0698 (linux-vdso.so.1+0x698)
#4 0x0000ffff80285140 raise (/lib64/libc.so.6+0x33140)
#5 0x0000ffff802864ec abort (/lib64/libc.so.6+0x344ec)
#6 0x0000ffff8027e54c __assert_fail_base (/lib64/libc.so.6+0x2c54c)
#7 0x0000ffff8027e5cc (/lib64/libc.so.6+0x2c5cc)
#8 0x0000aaaad323efb8 llvm::DenseMap<llvm::WeakVH,
llvm::detail::DenseSetEmpty, llvm::DenseMapInfo<llvm::WeakVH>,
llvm::detail::DenseSetPair<llvm::WeakVH> >::grow(unsigned int)
(/home/for_upload/llvm-project_1141/install/bin/clang-10+0x1f45fb8)
#9 0x0000aaaad323f170 llvm::SetVector<llvm::WeakVH,
llvm::SmallVector<llvm::WeakVH, 8u>, llvm::DenseSet<llvm::WeakVH,
llvm::DenseMapInfo<llvm::WeakVH> > >::insert(llvm::WeakVH const&)
(/home/for_upload/llvm-project_1141/install/bin/clang-10+0x1f46170)

This error is non-deterministic (does not show up in all compilation).

Could anyone tell me what might be going on?

PS:  In all the use cases of WeakVH, I see a Vector type is used
(never a SetVector).  Is the error something to do with that?  Should
I switch to use a Vector of WeakVH instead?

Thank you so much for your help.