[CHR] Fix crash when marking merged condition unknown (#173902) CHR builds the merged hot-path predicate with IRBuilder::CreateLogicalAnd. That helper is implemented as a select and can constant-fold to a non- Instruction (e.g. i1 true). The pass then attempted to mark the merged condition as having explicitly unknown branch weights when profile data is present, but it unconditionally did cast<Instruction>(MergedCondition), which can crash in release builds. Guard the metadata update with dyn_cast<Instruction> and pass the containing Function explicitly to avoid calling Instruction::getFunction when the value is not attached yet. Add a regression test that exercises the constant-folding case. Crashing stack: ``` 2. Running pass "chr" on function "repro_crash" #0 0x0000000003be00a4 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (bin/opt+0x3be00a4) #1 0x0000000003bdd9e8 llvm::sys::RunSignalHandlers() (bin/opt+0x3bdd9e8) #2 0x0000000003be1300 SignalHandler(int, siginfo_t*, void*) Signals.cpp:0:0 #3 0x0000ffffa8e1d840 (linux-vdso.so.1+0x840) #4 0x0000000003c815e0 llvm::Instruction::getFunction() const (bin/opt+0x3c815e0) #5 0x0000000003dcd35c llvm::setExplicitlyUnknownBranchWeightsIfProfiled(llvm::Instruction&, llvm::StringRef, llvm::Function const*) (bin/opt+0x3dcd35c) #6 0x0000000004fb3670 (anonymous namespace)::CHR::addToMergedCondition(bool, llvm::Value*, llvm::Instruction*, (anonymous namespace)::CHRScope*, llvm::IRBuilder<llvm::ConstantFolder, llvm::IRBuilderDefaultInserter>&, llvm::Value*&) ControlHeightReduction.cpp:0:0 #7 0x0000000004fa7d88 (anonymous namespace)::CHR::run() ControlHeightReduction.cpp:0:0 #8 0x0000000004fa3618 llvm::ControlHeightReductionPass::run(llvm::Function&, llvm::AnalysisManager<llvm::Function>&) (bin/opt+0x4fa3618) ``` Tests: opt < llvm/test/Transforms/PGOProfile/chr-unknown-profdata-crash.ll -passes='require<profile-summary>,function(chr)' -force-chr -chr-merge-threshold=1 -disable-output
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