[llvm-bugs] [Bug 46750] New: Crash in BitcodeReader.cpp under LTO

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=46750

            Bug ID: 46750
           Summary: Crash in BitcodeReader.cpp under LTO
           Product: tools
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: llc
          Assignee: unassignedbugs at nondot.org
          Reporter: chenmindong120 at gmail.com
                CC: llvm-bugs at lists.llvm.org

Created attachment 23736
  --> https://bugs.llvm.org/attachment.cgi?id=23736&action=edit
reduced c code

$ clang -O2 -flto=full test.c -o test.o
Or
$ llvm-dis test.o
llvm/lib/IR/Value.cpp:404: void llvm::Value::doRAUW(llvm::Value*,
llvm::Value::ReplaceMetadataUses): Assertion `New->getType() == getType() &&
"replaceAllUses of value with new value of different type!"' failed.

After some trouble shooting, I think the root is it's when parseConstants() in
BitcodeReader reads in a CST_CODE_CE_SELECT record, e.g.

select <selty><cond>, <ty><val1>, <ty><val2>

If “ty” here is a vector type and “cond” is a forward reference, LLVM uses i1
as the placeholder type of “cond” if it cannot find “cond” in ValueList, as the
code follows:

Type *SelectorTy = Type::getInt1Ty(Context);

// The selector might be an i1 or an <n x i1>
// Get the type from the ValueList before getting a forward ref.
if (VectorType *VTy = dyn_cast<VectorType>(CurTy))
if (Value *V = ValueList[Record[0]])
  if (SelectorTy != V->getType())
    SelectorTy = VectorType::get(SelectorTy, VTy->getNumElements()); 


However, the program aborts in RAUW() if we find “selty” is a vector type
later, because LLVM are trying to replace an i1 placeholder with an <n x i1>
value.

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