[llvm-bugs] [Bug 27133] New: clang-cl: LLVM lib/Transforms/Scalar/IndVarSimplify.cpp WidenIV::widenIVUse: dereference getFirstInsertionPt() == end()

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=27133

            Bug ID: 27133
           Summary: clang-cl: LLVM
                    lib/Transforms/Scalar/IndVarSimplify.cpp
                    WidenIV::widenIVUse: dereference getFirstInsertionPt()
                    == end()
           Product: clang
           Version: trunk
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: -New Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: stephan.bergmann.secondary at googlemail.com
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

At least on recent trunk r264857, attached (non-reduced) reproducer crashes
clang-cl, as

  IRBuilder<> Builder(&*WidePhi->getParent()->getFirstInsertionPt());

in WidenIV::widenIVUse (LLVM lib/Transforms/Scalar/IndVarSimplify.cpp)
dereferences an at-the-end iterator.

With

> --- a/lib/Transforms/Scalar/IndVarSimplify.cpp
> +++ b/lib/Transforms/Scalar/IndVarSimplify.cpp
> @@ -1287,7 +1287,10 @@ Instruction *WidenIV::widenIVUse(NarrowIVDefUse DU, SCEVExpander &Rewriter) {
>            PHINode::Create(DU.WideDef->getType(), 1, UsePhi->getName() + ".wide",
>                            UsePhi);
>          WidePhi->addIncoming(DU.WideDef, UsePhi->getIncomingBlock(0));
> -        IRBuilder<> Builder(&*WidePhi->getParent()->getFirstInsertionPt());
> +auto bb = WidePhi->getParent();
> +auto i = bb->getFirstInsertionPt();
> +assert(i != bb->end());
> +        IRBuilder<> Builder(&*i);
>          Value *Trunc = Builder.CreateTrunc(WidePhi, DU.NarrowDef->getType());
>          UsePhi->replaceAllUsesWith(Trunc);
>          DeadInsts.emplace_back(UsePhi);

the assertion fires at

> __GI___assert_fail at assert.c:101
> (anonymous namespace)::WidenIV::widenIVUse at llvm/lib/Transforms/Scalar/IndVarSimplify.cpp:1292
> (anonymous namespace)::WidenIV::createWideIV at llvm/lib/Transforms/Scalar/IndVarSimplify.cpp:1474
> (anonymous namespace)::IndVarSimplify::simplifyAndExtend at llvm/lib/Transforms/Scalar/IndVarSimplify.cpp:1561
> (anonymous namespace)::IndVarSimplify::runOnLoop at llvm/lib/Transforms/Scalar/IndVarSimplify.cpp:2168
> llvm::LPPassManager::runOnFunction at llvm/lib/Analysis/LoopPass.cpp:198
> llvm::FPPassManager::runOnFunction at llvm/lib/IR/LegacyPassManager.cpp:1550
> (anonymous namespace)::CGPassManager::RunPassOnSCC at llvm/lib/Analysis/CallGraphSCCPass.cpp:150
> (anonymous namespace)::CGPassManager::RunAllPassesOnSCC at llvm/lib/Analysis/CallGraphSCCPass.cpp:419
> (anonymous namespace)::CGPassManager::runOnModule at llvm/lib/Analysis/CallGraphSCCPass.cpp:474
> (anonymous namespace)::MPPassManager::runOnModule at llvm/lib/IR/LegacyPassManager.cpp:1627
> llvm::legacy::PassManagerImpl::run at llvm/lib/IR/LegacyPassManager.cpp:1730
> llvm::legacy::PassManager::run at llvm/lib/IR/LegacyPassManager.cpp:1761
> (anonymous namespace)::EmitAssemblyHelper::EmitAssembly at llvm/tools/clang/lib/CodeGen/BackendUtil.cpp:702
> clang::EmitBackendOutput at llvm/tools/clang/lib/CodeGen/BackendUtil.cpp:719
> clang::BackendConsumer::HandleTranslationUnit at llvm/tools/clang/lib/CodeGen/CodeGenAction.cpp:178
> clang::ParseAST at llvm/tools/clang/lib/Parse/ParseAST.cpp:168
> clang::ASTFrontendAction::ExecuteAction at llvm/tools/clang/lib/Frontend/FrontendAction.cpp:557
> clang::CodeGenAction::ExecuteAction at llvm/tools/clang/lib/CodeGen/CodeGenAction.cpp:822
> clang::FrontendAction::Execute at llvm/tools/clang/lib/Frontend/FrontendAction.cpp:457
> clang::CompilerInstance::ExecuteAction at llvm/tools/clang/lib/Frontend/CompilerInstance.cpp:873
> clang::ExecuteCompilerInvocation at llvm/tools/clang/lib/FrontendTool/ExecuteCompilerInvocation.cpp:241
> cc1_main at llvm/tools/clang/tools/driver/cc1_main.cpp:116
> ExecuteCC1Tool at llvm/tools/clang/tools/driver/driver.cpp:301
> main at llvm/tools/clang/tools/driver/driver.cpp:366

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