| Issue |
182775
|
| Summary |
Crash during loop optimization
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
sesse
|
This is minimized from a (huge, vector-intrinsic-heavy) program:
```c++
long *a;
void o() {
for (unsigned b;; ++b)
for (unsigned c = b; c < 4; ++c)
for (unsigned d = c; d; ++d)
for (unsigned e = d; e; ++e)
for (unsigned f = e; f; ++f)
for (unsigned g = f; g; ++g)
for (unsigned l = g; l; ++l)
for (; a[c];)
for (unsigned h = l; h < 4; ++h)
for (unsigned i = h; i < 4; ++i)
for (unsigned j = i; j < 4; ++j)
for (long k[j]; a;)
for (unsigned m = j; m < 4; ++m)
for (long n = a[m]; n; n = 1)
;
}
```
Compiling with `clang++-23 -O -std=c++20 -c foo.cc` on `Debian clang version 23.0.0 (++20260204101751+dd02b404b020-1~exp1)` yields:
```
foo.cc:14:37: warning: variable length arrays in C++ are a Clang extension [-Wvla-cxx-extension]
14 | for (long k[j]; a;)
| ^
foo.cc:14:37: note: read of non-const variable 'j' is not allowed in a constant _expression_
foo.cc:13:37: note: declared here
13 | for (unsigned j = i; j < 4; ++j)
| ^
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace, preprocessed source, and associated run script.
Stack dump:
0. Program arguments: clang++-23 -O -std=c++20 -c foo.cc
1. <eof> parser at end of file
2. Optimizer
3. Running pass "require<globals-aa>,function(invalidate<aa>),require<profile-summary>,cgscc(devirt<4>(inline,function-attrs<skip-non-recursive-function-attrs>,function<eager-inv;no-rerun>(sroa<modify-cfg>,early-cse<memssa>,simplifycfg<bonus-inst-threshold=1;no-forward-switch-cond;switch-range-to-icmp;no-switch-to-arithmetic;no-switch-to-lookup;keep-loops;no-hoist-common-insts;no-hoist-loads-stores-with-cond-faulting;no-sink-common-insts;speculate-blocks;simplify-cond-branch;no-speculate-unpredictables>,instcombine<max-iterations=1;no-verify-fixpoint>,libcalls-shrinkwrap,simplifycfg<bonus-inst-threshold=1;no-forward-switch-cond;switch-range-to-icmp;no-switch-to-arithmetic;no-switch-to-lookup;keep-loops;no-hoist-common-insts;no-hoist-loads-stores-with-cond-faulting;no-sink-common-insts;speculate-blocks;simplify-cond-branch;no-speculate-unpredictables>,reassociate,loop-mssa(loop-instsimplify,loop-simplifycfg,licm<no-allowspeculation>,loop-rotate<header-duplication;no-prepare-for-lto>,licm<allowspeculation>,simple-loop-unswitch<no-nontrivial;trivial>),simplifycfg<bonus-inst-threshold=1;no-forward-switch-cond;switch-range-to-icmp;no-switch-to-arithmetic;no-switch-to-lookup;keep-loops;no-hoist-common-insts;no-hoist-loads-stores-with-cond-faulting;no-sink-common-insts;speculate-blocks;simplify-cond-branch;no-speculate-unpredictables>,instcombine<max-iterations=1;no-verify-fixpoint>,loop(loop-idiom,indvars,loop-deletion,loop-unroll-full),sroa<modify-cfg>,memcpyopt,sccp,bdce,instcombine<max-iterations=1;no-verify-fixpoint>,coro-elide,adce,simplifycfg<bonus-inst-threshold=1;no-forward-switch-cond;switch-range-to-icmp;no-switch-to-arithmetic;no-switch-to-lookup;keep-loops;no-hoist-common-insts;no-hoist-loads-stores-with-cond-faulting;no-sink-common-insts;speculate-blocks;simplify-cond-branch;no-speculate-unpredictables>,instcombine<max-iterations=1;no-verify-fixpoint>),function-attrs,function(require<should-not-run-function-passes>),coro-split,coro-annotation-elide)),function(invalidate<should-not-run-function-passes>),cgscc(devirt<4>())" on module "foo.cc"
4. Running pass "cgscc(devirt<4>(inline,function-attrs<skip-non-recursive-function-attrs>,function<eager-inv;no-rerun>(sroa<modify-cfg>,early-cse<memssa>,simplifycfg<bonus-inst-threshold=1;no-forward-switch-cond;switch-range-to-icmp;no-switch-to-arithmetic;no-switch-to-lookup;keep-loops;no-hoist-common-insts;no-hoist-loads-stores-with-cond-faulting;no-sink-common-insts;speculate-blocks;simplify-cond-branch;no-speculate-unpredictables>,instcombine<max-iterations=1;no-verify-fixpoint>,libcalls-shrinkwrap,simplifycfg<bonus-inst-threshold=1;no-forward-switch-cond;switch-range-to-icmp;no-switch-to-arithmetic;no-switch-to-lookup;keep-loops;no-hoist-common-insts;no-hoist-loads-stores-with-cond-faulting;no-sink-common-insts;speculate-blocks;simplify-cond-branch;no-speculate-unpredictables>,reassociate,loop-mssa(loop-instsimplify,loop-simplifycfg,licm<no-allowspeculation>,loop-rotate<header-duplication;no-prepare-for-lto>,licm<allowspeculation>,simple-loop-unswitch<no-nontrivial;trivial>),simplifycfg<bonus-inst-threshold=1;no-forward-switch-cond;switch-range-to-icmp;no-switch-to-arithmetic;no-switch-to-lookup;keep-loops;no-hoist-common-insts;no-hoist-loads-stores-with-cond-faulting;no-sink-common-insts;speculate-blocks;simplify-cond-branch;no-speculate-unpredictables>,instcombine<max-iterations=1;no-verify-fixpoint>,loop(loop-idiom,indvars,loop-deletion,loop-unroll-full),sroa<modify-cfg>,memcpyopt,sccp,bdce,instcombine<max-iterations=1;no-verify-fixpoint>,coro-elide,adce,simplifycfg<bonus-inst-threshold=1;no-forward-switch-cond;switch-range-to-icmp;no-switch-to-arithmetic;no-switch-to-lookup;keep-loops;no-hoist-common-insts;no-hoist-loads-stores-with-cond-faulting;no-sink-common-insts;speculate-blocks;simplify-cond-branch;no-speculate-unpredictables>,instcombine<max-iterations=1;no-verify-fixpoint>),function-attrs,function(require<should-not-run-function-passes>),coro-split,coro-annotation-elide))" on module "foo.cc"
5. Running pass "loop(loop-idiom,indvars,loop-deletion,loop-unroll-full)" on function "_Z1ov"
#0 0x00007f79cd54431a llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/usr/lib/llvm-23/bin/../lib/libLLVM.so.23.0+0x4d4431a)
#1 0x00007f79cd541b47 llvm::sys::RunSignalHandlers() (/usr/lib/llvm-23/bin/../lib/libLLVM.so.23.0+0x4d41b47)
#2 0x00007f79cd46fd34 (/usr/lib/llvm-23/bin/../lib/libLLVM.so.23.0+0x4c6fd34)
#3 0x00007f79c824aa70 (/usr/lib/x86_64-linux-gnu/libc.so.6+0x40a70)
#4 0x00007f79c95bdfc0 (/usr/lib/llvm-23/bin/../lib/libLLVM.so.23.0+0xdbdfc0)
clang++-23: error: clang frontend command failed with exit code 139 (use -v to see invocation)
Debian clang version 23.0.0 (++20260204101751+dd02b404b020-1~exp1)
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/lib/llvm-23/bin
clang++-23: note: diagnostic msg:
********************
PLEASE ATTACH THE FOLLOWING FILES TO THE BUG REPORT:
Preprocessed source(s) and associated run script(s) are located at:
clang++-23: note: diagnostic msg: /tmp/foo-5bbb4a.cpp
clang++-23: note: diagnostic msg: /tmp/foo-5bbb4a.sh
clang++-23: note: diagnostic msg:
********************
```
This worked with Clang 19, but fails in the same way on Clang 20, 21 and 22.
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