[LLVMbugs] [Bug 20982] New: UBSan error in lib/Target/R600/AMDGPUISelLowering.cpp (left shift of negative value)

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=20982

            Bug ID: 20982
           Summary: UBSan error in lib/Target/R600/AMDGPUISelLowering.cpp
                    (left shift of negative value)
           Product: new-bugs
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: vonosmas at gmail.com
                CC: llvmbugs at cs.uiuc.edu, tstellar at gmail.com
            Blocks: 20815
    Classification: Unclassified

The following R600 test fails under UBSan bootstrap of LLVM:

    LLVM :: CodeGen/R600/llvm.AMDGPU.bfe.i32.ll

The problem is the left shift of negative value in llvm::SDValue
constantFoldBFE<int32_t> in AMDGPUISelLowering.cpp (left shift of negative
value is undefined behavior in C).

To reproduce: build LLVM with just-built Clang and
-DLLVM_USE_SANITIZER=Undefined CMake option. I'm going to disable this specific
test case under UBSan, so that suppression will have to be removed as well.

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