[llvm] [SimplifyCFG] Updated early exit in `CanRedirectPredsOfEmptyBBToSucc` (PR #142582)

Tue Jun 3 05:07:26 PDT 2025

https://github.com/dtcxzyw requested changes to this pull request.

Infinite loop reproducer:
```
; bin/opt -passes=simplifycfg test.ll -S
target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"

define void @func_143(i32 %0, ptr %g_329) {
entry:
  switch i32 %0, label %common.ret [
    i32 0, label %for.inc295
    i32 1, label %for.end297
    i32 33, label %for.inc295
  ]

for.inc295:                                       ; preds = %entry, %entry
  br label %for.end297

common.ret:                                       ; preds = %for.end297, %entry
  ret void

for.end297:                                       ; preds = %for.inc295, %entry
  %storemerge739.lcssa761 = phi i64 [ 0, %entry ], [ 1, %for.inc295 ]
  store i8 0, ptr %g_329, align 1
  br label %common.ret
}
```

```
opt: /home/dtcxzyw/WorkSpace/Projects/compilers/llvm-project/llvm/lib/Transforms/Scalar/SimplifyCFGPass.cpp:249: bool iterativelySimplifyCFG(llvm::Function&, const llvm::TargetTransformInfo&, llvm::DomTreeUpdater*, const llvm::SimplifyCFGOptions&): Assertion `IterCnt++ < 1000 && "Iterative simplification didn't converge!"' failed.
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace.
Stack dump:
0.      Program arguments: ./bin/opt -passes=simplifycfg reduced.ll -S
1.      Running pass "function(simplifycfg<bonus-inst-threshold=1;no-forward-switch-cond;no-switch-range-to-icmp;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>)" on module "reduced.ll"
2.      Running pass "simplifycfg<bonus-inst-threshold=1;no-forward-switch-cond;no-switch-range-to-icmp;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>" on function "func_143"
 #0 0x0000728e8f8279f2 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/home/dtcxzyw/WorkSpace/Projects/compilers/LLVM/llvm-build/bin/../lib/libLLVMSupport.so.21.0git+0x2279f2)
 #1 0x0000728e8f8248cf llvm::sys::RunSignalHandlers() (/home/dtcxzyw/WorkSpace/Projects/compilers/LLVM/llvm-build/bin/../lib/libLLVMSupport.so.21.0git+0x2248cf)
 #2 0x0000728e8f824a14 SignalHandler(int, siginfo_t*, void*) Signals.cpp:0:0
 #3 0x0000728e8f245330 (/lib/x86_64-linux-gnu/libc.so.6+0x45330)
 #4 0x0000728e8f29eb2c __pthread_kill_implementation ./nptl/pthread_kill.c:44:76
 #5 0x0000728e8f29eb2c __pthread_kill_internal ./nptl/pthread_kill.c:78:10
 #6 0x0000728e8f29eb2c pthread_kill ./nptl/pthread_kill.c:89:10
 #7 0x0000728e8f24527e raise ./signal/../sysdeps/posix/raise.c:27:6
 #8 0x0000728e8f2288ff abort ./stdlib/abort.c:81:7
 #9 0x0000728e8f22881b _nl_load_domain ./intl/loadmsgcat.c:1177:9
#10 0x0000728e8f23b517 (/lib/x86_64-linux-gnu/libc.so.6+0x3b517)
#11 0x0000728e873b78e5 iterativelySimplifyCFG(llvm::Function&, llvm::TargetTransformInfo const&, llvm::DomTreeUpdater*, llvm::SimplifyCFGOptions const&) SimplifyCFGPass.cpp:0:0
#12 0x0000728e873b852c simplifyFunctionCFGImpl(llvm::Function&, llvm::TargetTransformInfo const&, llvm::DominatorTree*, llvm::SimplifyCFGOptions const&) SimplifyCFGPass.cpp:0:0
#13 0x0000728e873b93b5 simplifyFunctionCFG(llvm::Function&, llvm::TargetTransformInfo const&, llvm::DominatorTree*, llvm::SimplifyCFGOptions const&) SimplifyCFGPass.cpp:0:0
#14 0x0000728e873b9510 llvm::SimplifyCFGPass::run(llvm::Function&, llvm::AnalysisManager<llvm::Function>&) (/home/dtcxzyw/WorkSpace/Projects/compilers/LLVM/llvm-build/bin/../lib/../lib/libLLVMScalarOpts.so.21.0git+0x3b9510)
#15 0x0000728e893ac495 llvm::detail::PassModel<llvm::Function, llvm::SimplifyCFGPass, llvm::AnalysisManager<llvm::Function>>::run(llvm::Function&, llvm::AnalysisManager<llvm::Function>&) (/home/dtcxzyw/WorkSpace/Projects/compilers/LLVM/llvm-build/bin/../lib/../lib/libPolly.so.21.0git+0x1ac495)
#16 0x0000728e85d27164 llvm::PassManager<llvm::Function, llvm::AnalysisManager<llvm::Function>>::run(llvm::Function&, llvm::AnalysisManager<llvm::Function>&) (/home/dtcxzyw/WorkSpace/Projects/compilers/LLVM/llvm-build/bin/../lib/../lib/libLLVMCore.so.21.0git+0x327164)
#17 0x0000728e8e2db7c5 llvm::detail::PassModel<llvm::Function, llvm::PassManager<llvm::Function, llvm::AnalysisManager<llvm::Function>>, llvm::AnalysisManager<llvm::Function>>::run(llvm::Function&, llvm::AnalysisManager<llvm::Function>&) (/home/dtcxzyw/WorkSpace/Projects/compilers/LLVM/llvm-build/bin/../lib/../lib/libLLVMX86CodeGen.so.21.0git+0xdb7c5)
#18 0x0000728e85d27680 llvm::ModuleToFunctionPassAdaptor::run(llvm::Module&, llvm::AnalysisManager<llvm::Module>&) (/home/dtcxzyw/WorkSpace/Projects/compilers/LLVM/llvm-build/bin/../lib/../lib/libLLVMCore.so.21.0git+0x327680)
#19 0x0000728e8e2dc185 llvm::detail::PassModel<llvm::Module, llvm::ModuleToFunctionPassAdaptor, llvm::AnalysisManager<llvm::Module>>::run(llvm::Module&, llvm::AnalysisManager<llvm::Module>&) (/home/dtcxzyw/WorkSpace/Projects/compilers/LLVM/llvm-build/bin/../lib/../lib/libLLVMX86CodeGen.so.21.0git+0xdc185)
#20 0x0000728e85d28805 llvm::PassManager<llvm::Module, llvm::AnalysisManager<llvm::Module>>::run(llvm::Module&, llvm::AnalysisManager<llvm::Module>&) (/home/dtcxzyw/WorkSpace/Projects/compilers/LLVM/llvm-build/bin/../lib/../lib/libLLVMCore.so.21.0git+0x328805)
#21 0x0000728e8f9f23d9 llvm::runPassPipeline(llvm::StringRef, llvm::Module&, llvm::TargetMachine*, llvm::TargetLibraryInfoImpl*, llvm::ToolOutputFile*, llvm::ToolOutputFile*, llvm::ToolOutputFile*, llvm::StringRef, llvm::ArrayRef<llvm::PassPlugin>, llvm::ArrayRef<std::function<void (llvm::PassBuilder&)>>, llvm::opt_tool::OutputKind, llvm::opt_tool::VerifierKind, bool, bool, bool, bool, bool, bool, bool) (/home/dtcxzyw/WorkSpace/Projects/compilers/LLVM/llvm-build/bin/../lib/libLLVMOptDriver.so.21.0git+0x2d3d9)
#22 0x0000728e8f9fd416 optMain (/home/dtcxzyw/WorkSpace/Projects/compilers/LLVM/llvm-build/bin/../lib/libLLVMOptDriver.so.21.0git+0x38416)
#23 0x0000728e8f22a1ca __libc_start_call_main ./csu/../sysdeps/nptl/libc_start_call_main.h:74:3
#24 0x0000728e8f22a28b call_init ./csu/../csu/libc-start.c:128:20
#25 0x0000728e8f22a28b __libc_start_main ./csu/../csu/libc-start.c:347:5
#26 0x0000637447eb2095 _start (./bin/opt+0x1095)

Aborted (core dumped)
```

https://github.com/llvm/llvm-project/pull/142582