[LLVMbugs] [Bug 7713] New: DAGCombiner crashes during phase 2 of Release Clang self-host

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=7713

           Summary: DAGCombiner crashes during phase 2 of Release Clang
                    self-host
           Product: libraries
           Version: trunk
          Platform: PC
        OS/Version: MacOS X
            Status: NEW
          Severity: normal
          Priority: P
         Component: Common Code Generator Code
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: cdavis at mymail.mines.edu
                CC: llvmbugs at cs.uiuc.edu


Created an attachment (id=5267)
 --> (http://llvm.org/bugs/attachment.cgi?id=5267)
Stack trace from Clang crashing inside DAG Combiner

I've hit a serious bug in CodeGen. I don't know exactly what it is, but I do
know that LLVM crashes somewhere in the DAG Combiner under certain
circumstances.

This only happens when LLVM and Clang are built Release without Asserts by
recent (i.e. trunk) Clang. Building Debug or +Asserts causes the problem to go
away. This has slipped past the buildbots because they all build either Debug
or +Asserts.

An example stack trace is attached. I produced it compiling addvdi3.c from the
compiler-rt project. Running the test suite produced all sorts of similar (but
not quite the same) stack traces. Different code causes crashes in different
parts of the DAG Combiner, but the crash is always (from what I've seen,
anyway) in the DAG Combiner.

I also know that the crash happens when the DAG Combiner tries to dereference a
NULL SDNode. How could CodeGen produce a DAG with a NULL SDNode?

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