[llvm-bugs] [Bug 36683] New: Error "Do not know how to split this operator's operand!" after "Add ARMv8.2-A FP16 vector intrinsic"

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=36683

            Bug ID: 36683
           Summary: Error "Do not know how to split this operator's
                    operand!" after "Add ARMv8.2-A FP16 vector intrinsic"
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Backend: ARM
          Assignee: unassignedbugs at nondot.org
          Reporter: martin at martin.st
                CC: llvm-bugs at lists.llvm.org

Created attachment 20046
  --> https://bugs.llvm.org/attachment.cgi?id=20046&action=edit
Reduced source code that triggers the error

Commit SVN r327189 in clang ([ARM] Add ARMv8.2-A FP16 vector intrinsic) caused
the following test C code to change the output IR:

    typedef __attribute__((neon_vector_type(4))) __fp16 float16x4_t;
    void fn1() {
      __fp16 *out_f16;
      float16x4_t __s1;
      __builtin_neon_vst1_v(out_f16, __s1, 8);
    }

When built e.g. like this, "clang -target armv7-linux-gnueabihf -c
qfloat16-reduced.c -O2", it errors out with the following message:

> SplitVectorOperand Op #3: t5: ch = llvm.arm.neon.vst1<ST8[undef](align=2)> t0, TargetConstant:i32<716>, undef:i32, undef:v4f16, Constant:i32<2>
>   
> fatal error: error in backend: Do not know how to split this operator's operand!
> 
> clang-7.0: error: clang frontend command failed with exit code 70 (use -v to see invocation)
> clang version 7.0.0 (http://llvm.org/git/clang 72858dcc190c6438930f3cc17a134ed6195f6a15) (llvm/trunk 327197)"

The generated LLVM IR after the change, that fails also when run through llc,
is the following:

    define void @fn1() {
    entry:
      tail call void @llvm.arm.neon.vst1.p0i8.v4f16(i8* undef, <4 x half>
undef, i32 2)
      ret void
    }

    declare void @llvm.arm.neon.vst1.p0i8.v4f16(i8*, <4 x half>, i32)

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