[LLVMbugs] [Bug 5663] New: Lazy bitcode loading interacts badly with global opts

[bugzilla-daemon at cs.uiuc.edu]

http://llvm.org/bugs/show_bug.cgi?id=5663

           Summary: Lazy bitcode loading interacts badly with global opts
           Product: libraries
           Version: trunk
          Platform: PC
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Core LLVM classes
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: jyasskin at google.com
                CC: llvmbugs at cs.uiuc.edu


Created an attachment (id=3904)
 --> (http://llvm.org/bugs/attachment.cgi?id=3904)
C++ program demonstrating bad behavior

$ g++ `llvm-config --cxxflags --ldflags --libs` modprovider_crash.cpp -o
modprovider_crash -Wall -g
$ llvm-as modprovider_crash.ll 
$ ./modprovider_crash modprovider_crash.bc 
LLVM ERROR: Error reading bitcode file: Invalid LOAD record
$ 

At ToT, globaldce deletes functions with ghost linkage, which forgets the fact
that the BitcodeReader can materialize them from the backing file.

With the attached patch, we get the above problem instead, where globaldce
doesn't realize that @globl has a user hidden away in the bitcode file.
Globaldce then deletes @globl which causes ModuleProvider::materializeFunction
to fail.

deadargelim is likely to have a similar problem when it thinks it can eliminate
an argument to a function but can't update callers hidden in the bitcode.


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