[llvm-bugs] [Bug 33682] New: endianness bug in visitTRUNCATE

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Mon Jul 3 11:27:52 PDT 2017


            Bug ID: 33682
           Summary: endianness bug in visitTRUNCATE
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Common Code Generator Code
          Assignee: unassignedbugs at nondot.org
          Reporter: pichet2000 at gmail.com
                CC: llvm-bugs at lists.llvm.org

// Fold truncate of a bitcast of a vector to an extract of the low vector
  // element.
  // e.g. trunc (i64 (bitcast v2i32:x)) -> extract_vector_elt v2i32:x, 0

This is not true on big-endian architecture.

      return DAG.getNode(ISD::EXTRACT_VECTOR_ELT, SL, VT,
                         VecSrc, DAG.getConstant(0, SL, IdxVT));
Should be replaced by:

      unsigned Idx = DAG.getDataLayout().isBigEndian() ? 1 : 0;
      return DAG.getNode(ISD::EXTRACT_VECTOR_ELT, SL, VT,
                         VecSrc, DAG.getConstant(Idx, SL, IdxVT));

I found this while investigating codegen failure on an out of test big-endian

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