[llvm-bugs] [Bug 39893] New: Assertion failed: `NumElements > 0 && "#Elements of a VectorType must be greater than 0"'

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=39893

            Bug ID: 39893
           Summary: Assertion failed: `NumElements > 0 && "#Elements of a
                    VectorType must be greater than 0"'
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Common Code Generator Code
          Assignee: unassignedbugs at nondot.org
          Reporter: russell_gallop at sn.scee.net
                CC: llvm-bugs at lists.llvm.org

$ cat test.cpp
typedef int __attribute__((ext_vector_type(2))) d;
typedef char __attribute__((ext_vector_type(2))) e;
typedef char __attribute__((ext_vector_type(8))) f;
typedef union {
  d a;
  f b;
} g;
f h;
d j;
void k() {
  g l;
  l.a = - j;
  volatile e m = __builtin_shufflevector(h, l.b, 10, 4);
}
$ clang -c -O1 test.cpp
clang-8: .../llvm/lib/IR/Type.cpp:607: static llvm::VectorType*
llvm::VectorType::get(llvm::Type*, unsigned int): Assertion `NumElements > 0 &&
"#Elements of a VectorType must be greater than 0"' failed.

Introduced at r345602.

Author: Sanjay Patel <spatel at rotateright.com>
Date:   Tue Oct 30 14:14:34 2018 +0000

[DAGCombiner] narrow vector binops when extraction is cheap

    Narrowing vector binops came up in the demanded bits discussion in D52912.

    I don't think we're going to be able to do this transform in IR as a
canonicalization
    because of the risk of creating unsupported widths for vector ops, but we
already have
    a DAG TLI hook to allow what I was hoping for: isExtractSubvectorCheap().
This is
    currently enabled for x86, ARM, and AArch64 (although only x86 has existing
regression
    test diffs).

    This is artificially limited to not look through bitcasts because there are
so many
    test diffs already, but that's marked with a TODO and is a small follow-up.

    Differential Revision: https://reviews.llvm.org/D53784

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