[llvm-bugs] [Bug 27550] New: [ARM] fp16 neon intrinsics are available even the target doesn't support fp16

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https://llvm.org/bugs/show_bug.cgi?id=27550

            Bug ID: 27550
           Summary: [ARM] fp16 neon intrinsics are available even the
                    target doesn't support fp16
           Product: clang
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: -New Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: silviu.baranga at arm.com
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

The following code:

#include <arm_neon.h>

float16x4_t f(float32x4_t x) {
  return vcvt_f16_f32(x);
}

compiled with:

clang -target armv7-linux-gnueabi -mfpu=neon rep.c
-I/usr/include/arm-linux-gnueabihf -mfloat-abi=hard

triggers an assert in instruction selection:

fatal error: error in backend: Cannot select: intrinsic
%llvm.arm.neon.vcvtfp2hf

This is because we're using the vcvt_f16_f32 intrinsic and defined the fpu to
be neon (not neon-fp16), and therefore the target doesn't support the f16 vcvt
instruction.

We should be emitting an error in the frontend instead.

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