[LLVMbugs] [Bug 1788] New: assertion failure in lib/transforms/IPO/ DeadArgumentElimination

[bugzilla-daemon at cs.uiuc.edu]

http://llvm.org/bugs/show_bug.cgi?id=1788

           Summary: assertion failure in
                    lib/transforms/IPO/DeadArgumentElimination
           Product: new-bugs
           Version: unspecified
          Platform: PC
        OS/Version: Windows XP
            Status: NEW
          Severity: normal
          Priority: P2
         Component: new bugs
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: richard.smith at antixlabs.com
                CC: llvmbugs at cs.uiuc.edu


llvm-ld gives an assertion failure "CS.instruction() && Unknown instruction for
the I2I list" in lib/transforms/IPO/DeadArgumentElimination. The app which
provoked it is large and under NDA so cannot be attached, but the reason is
thus:

runOnModule in lib/transforms/IPO/DeadArgumentElimination.cpp iterates through
every function and -

(a) checks whether it has varargs but no va_start. If that is so the varargs
are removed and every call to the function is replaced with one which omits the
params;

(b) calls SurveyFunction, and if the funtion has "maybe alive" args, all calls
within the function are pushed to the vector InstructionsToInspect.

In this case, a function processed provokes (b) and pushes the addresses of a
number of call intructions to InstructionsToInspect, one of which is to a
function with unused varargs. Later in the iteration loop that function is
processed provoking (a) - it is modified and all calls to it are replaced. At
this point, InstructionsToInspect still contains a pointer to the original
call, which is now invalid.

When InstructionsToInspect is processed it reaches the invalid pointer and the
random data there happens to provoke the asserion failure reported.


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