[llvm-bugs] [Bug 38110] New: Loop vectorizer assertion failure in truncateToMinimalBitwidths

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=38110

            Bug ID: 38110
           Summary: Loop vectorizer assertion failure in
                    truncateToMinimalBitwidths
           Product: libraries
           Version: trunk
          Hardware: Other
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Loop Optimizer
          Assignee: unassignedbugs at nondot.org
          Reporter: uweigand at de.ibm.com
                CC: llvm-bugs at lists.llvm.org

Created attachment 20543
  --> https://bugs.llvm.org/attachment.cgi?id=20543&action=edit
Reduced test case

Running the attached test case through

  opt -loop-vectorize -mcpu=z13

on the s390x-ibm-linux target results in an assertion failure:

Unhandled instruction type!
UNREACHABLE executed at
/home/uweigand/llvm/llvm-head/lib/Transforms/Vectorize/LoopVectorize.cpp:3292!

The unhandled instruction at this point seems to be a phi node.

This is a reduced test case from a real-world application.  The corresponding
reduced C source code test case (same assertion failure) is:

void
test (unsigned int width, unsigned char *row,
      unsigned short src, unsigned short *dst)
{
  unsigned char *sp;
  unsigned int i;

  sp = row;
  for (i = 0; i < width; i++, sp++)
    {
      if (*sp == src)
        *sp = (unsigned char) *dst;
    }
}

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