[clang][aarch64] Support implicit casts between GNU and SVE vectors

[c-rhodes]

Summary

This patch adds support for implicit casting between GNU vectors and SVE
vectors when __ARM_FEATURE_SVE_BITS==N, as defined by the Arm C
Language Extensions (ACLE, version 00bet5, section 3.7.3.3) for SVE [1].

This behavior makes it possible to use GNU vectors with ACLE functions
that operate on VLAT. For example:

typedef int8_t vec __attribute__((vector_size(32)));
vec f(vec x) { return svasrd_x(svptrue_b8(), x, 1); }

Tests are also added for implicit casting between GNU and fixed-length
SVE vectors created by the 'arm_sve_vector_bits' attribute. This
behavior makes it possible to use VLST with existing interfaces that
operate on GNUT. For example:

typedef int8_t vec1 __attribute__((vector_size(32)));
void f(vec1);
#if __ARM_FEATURE_SVE_BITS==256 && __ARM_FEATURE_SVE_VECTOR_OPERATORS
typedef svint8_t vec2 __attribute__((arm_sve_vector_bits(256)));
void g(vec2 x) { f(x); } // OK
#endif

The __ARM_FEATURE_SVE_VECTOR_OPERATORS feature macro indicates
interoperability with the GNU vector extension. This is the first patch
providing support for this feature, which once complete will be enabled
by the -msve-vector-bits flag, as the __ARM_FEATURE_SVE_BITS feature
currently is.

[1] https://developer.arm.com/documentation/100987/latest

[efriedma]

clang/lib/AST/ASTContext.cpp

8522

We allow casting SVE fixed-width vectors only if the element type is identical, but we allow casting to GNU fixed-width vectors if the vector width is the same? That seems sort of loose; could allow weird casts, particularly when bool vectors are involved.

[c-rhodes]

clang/lib/AST/ASTContext.cpp

8522

We allow casting SVE fixed-width vectors only if the element type is identical, but we allow casting to GNU fixed-width vectors if the vector width is the same? That seems sort of loose; could allow weird casts, particularly when bool vectors are involved.

Fixed-length SVE vectors are created with the attribute and the vector width must match -msve-vector-bits, which should guarantee consistent vector widths for a given input. This is checking the vector width is the same and the element type matches when casting between GNU and SVE vectors, although since neither of those types are created by the attribute it's necessary to check the vector width to validate __ARM_FEATURE_SVE_BITS==N.

Predicates are treated differently in the ACLE and it doesn't mention supporting casts between GNU bool vectors and SVE VLS/VLA predicates. I'm also not sure the GNU vector_size extension is defined for bool elements yet, but I did notice Simon Moll is working on this (D81083).

[c-rhodes]

Added tests for implicit casts between GNU and fixed-length SVE vectors. I was planning to create a separate patch for this but since it's only tests and no functional changes I've included it in this patch.

[c-rhodes]

clang/test/Sema/attr-arm-sve-vector-bits.c

233–234

I expected similar diagnostics when casting between GNU and fixed-length SVE vectors where the element type doesn't match but the vector size is equal but that wasn't the case. Since no functional changes were necessary to support casting between these types I tried the following:

#include <stdint.h>

#define N 128

typedef float float32_t;
typedef double float64_t;

typedef float32_t gnu_float32_t __attribute__((vector_size(N/8)));
typedef float64_t gnu_float64_t __attribute__((vector_size(N/8)));

gnu_float32_t foo(gnu_float64_t x) { return (gnu_float32_t)x; }
gnu_float64_t bar(gnu_float32_t x) { return (gnu_float64_t)x; }

It seems Clang considers this implicit cast valid whereas GCC doesn't, even with lax vector conversions enabled.

[c-rhodes]

clang/test/Sema/attr-arm-sve-vector-bits.c

233–234

I pasted the wrong example, the explicit cast shouldn't be there:

#include <stdint.h>

#define N 128

typedef float float32_t;
typedef double float64_t;

typedef float32_t gnu_float32_t __attribute__((vector_size(N/8)));
typedef float64_t gnu_float64_t __attribute__((vector_size(N/8)));

gnu_float32_t foo(gnu_float64_t x) { return x; }
gnu_float64_t bar(gnu_float32_t x) { return x; }

[efriedma]

clang/lib/AST/ASTContext.cpp

8522

I think you need to check both the size and the element type here?

clang/test/Sema/attr-arm-sve-vector-bits.c

237

This test isn't checking what it says it is; int4 and svint64_t have different element types.

[c-rhodes]

clang/lib/AST/ASTContext.cpp

8522

I think you need to check both the size and the element type here?

Compare the size of a scalable and fixed-length vector?

[c-rhodes]

Address comments

clang/test/Sema/attr-arm-sve-vector-bits.c

237

This test isn't checking what it says it is; int4 and svint64_t have different element types.

Good spot! Fixed

[efriedma]

LGTM

clang/lib/AST/ASTContext.cpp

if (const auto *BT = FirstType->getAs<BuiltinType>()) {
       if (const auto *VT = SecondType->getAs<VectorType>()) {
         // Predicates have the same representation as uint8 so we also have to
         // check the kind to make these types incompatible.
         if (VT->getVectorKind() == VectorType::SveFixedLengthPredicateVector)
           return BT->getKind() == BuiltinType::SveBool;
         else if (VT->getVectorKind() == VectorType::SveFixedLengthDataVector)
           return VT->getElementType().getCanonicalType() ==
                  FirstType->getSveEltType(*this);
+        else if (VT->getVectorKind() == VectorType::GenericVector)
+          return getTypeSize(SecondType) == getLangOpts().ArmSveVectorBits &&
+                 hasSameType(VT->getElementType(),
+                             getBuiltinVectorTypeInfo(BT).ElementType);
       }
     }
     return false;
   };
 
   return IsValidCast(FirstType, SecondType) ||
          IsValidCast(SecondType, FirstType);
 }

clang/test/CodeGen/attr-arm-sve-vector-bits-cast.c

 // NOTE: Assertions have been autogenerated by utils/update_cc_test_checks.py
 // REQUIRES: aarch64-registered-target
 // RUN: %clang_cc1 -triple aarch64-none-linux-gnu -target-feature +sve -msve-vector-bits=512 -fallow-half-arguments-and-returns -S -O1 -emit-llvm -o - %s | FileCheck %s
 
 #include <arm_sve.h>
 
 #define N __ARM_FEATURE_SVE_BITS
 
 typedef svint32_t fixed_int32_t __attribute__((arm_sve_vector_bits(N)));
 typedef svfloat64_t fixed_float64_t __attribute__((arm_sve_vector_bits(N)));
 typedef svbool_t fixed_bool_t __attribute__((arm_sve_vector_bits(N)));
+typedef int32_t gnu_int32_t __attribute__((vector_size(N / 8)));
 
 // CHECK-LABEL: @to_svint32_t(
 // CHECK-NEXT:  entry:
 // CHECK-NEXT:    [[TYPE:%.*]] = alloca <16 x i32>, align 16
 // CHECK-NEXT:    [[TYPE_ADDR:%.*]] = alloca <16 x i32>, align 16
 // CHECK-NEXT:    [[TMP0:%.*]] = bitcast <16 x i32>* [[TYPE]] to <vscale x 4 x i32>*
 // CHECK-NEXT:    store <vscale x 4 x i32> [[TYPE_COERCE:%.*]], <vscale x 4 x i32>* [[TMP0]], align 16
 // CHECK-NEXT:    [[TYPE1:%.*]] = load <16 x i32>, <16 x i32>* [[TYPE]], align 16, [[TBAA2:!tbaa !.*]]

 // CHECK-NEXT:    [[TMP2:%.*]] = bitcast <vscale x 16 x i1>* [[RETVAL_COERCE]] to i64*
 // CHECK-NEXT:    store i64 [[TMP1]], i64* [[TMP2]], align 16
 // CHECK-NEXT:    [[TMP3:%.*]] = load <vscale x 16 x i1>, <vscale x 16 x i1>* [[RETVAL_COERCE]], align 16
 // CHECK-NEXT:    ret <vscale x 16 x i1> [[TMP3]]
 //
 fixed_bool_t from_svbool_t(svbool_t type) {
   return type;
 }
+
+// CHECK-LABEL: @to_svint32_t__from_gnu_int32_t(
+// CHECK-NEXT:  entry:
+// CHECK-NEXT:    [[TYPE_ADDR:%.*]] = alloca <16 x i32>, align 16
+// CHECK-NEXT:    [[TYPE:%.*]] = load <16 x i32>, <16 x i32>* [[TMP0:%.*]], align 16, [[TBAA2]]
+// CHECK-NEXT:    store <16 x i32> [[TYPE]], <16 x i32>* [[TYPE_ADDR]], align 16, [[TBAA2]]
+// CHECK-NEXT:    [[TMP1:%.*]] = bitcast <16 x i32>* [[TYPE_ADDR]] to <vscale x 4 x i32>*
+// CHECK-NEXT:    [[TMP2:%.*]] = load <vscale x 4 x i32>, <vscale x 4 x i32>* [[TMP1]], align 16, [[TBAA2]]
+// CHECK-NEXT:    ret <vscale x 4 x i32> [[TMP2]]
+//
+svint32_t to_svint32_t__from_gnu_int32_t(gnu_int32_t type) {
+  return type;
+}
+
+// CHECK-LABEL: @from_svint32_t__to_gnu_int32_t(
+// CHECK-NEXT:  entry:
+// CHECK-NEXT:    [[TYPE_ADDR:%.*]] = alloca <vscale x 4 x i32>, align 16
+// CHECK-NEXT:    store <vscale x 4 x i32> [[TYPE:%.*]], <vscale x 4 x i32>* [[TYPE_ADDR]], align 16, [[TBAA5]]
+// CHECK-NEXT:    [[TMP0:%.*]] = bitcast <vscale x 4 x i32>* [[TYPE_ADDR]] to <16 x i32>*
+// CHECK-NEXT:    [[TMP1:%.*]] = load <16 x i32>, <16 x i32>* [[TMP0]], align 16, [[TBAA2]]
+// CHECK-NEXT:    store <16 x i32> [[TMP1]], <16 x i32>* [[AGG_RESULT:%.*]], align 16, [[TBAA2]]
+// CHECK-NEXT:    ret void
+//
+gnu_int32_t from_svint32_t__to_gnu_int32_t(svint32_t type) {
+  return type;
+}
+
+// CHECK-LABEL: @to_fixed_int32_t__from_gnu_int32_t(
+// CHECK-NEXT:  entry:
+// CHECK-NEXT:    [[RETVAL_COERCE:%.*]] = alloca <vscale x 4 x i32>, align 16
+// CHECK-NEXT:    [[TYPE:%.*]] = load <16 x i32>, <16 x i32>* [[TMP0:%.*]], align 16, [[TBAA2]]
+// CHECK-NEXT:    [[RETVAL_0__SROA_CAST:%.*]] = bitcast <vscale x 4 x i32>* [[RETVAL_COERCE]] to <16 x i32>*
+// CHECK-NEXT:    store <16 x i32> [[TYPE]], <16 x i32>* [[RETVAL_0__SROA_CAST]], align 16
+// CHECK-NEXT:    [[TMP1:%.*]] = load <vscale x 4 x i32>, <vscale x 4 x i32>* [[RETVAL_COERCE]], align 16
+// CHECK-NEXT:    ret <vscale x 4 x i32> [[TMP1]]
+//
+fixed_int32_t to_fixed_int32_t__from_gnu_int32_t(gnu_int32_t type) {
+  return type;
+}
+
+// CHECK-LABEL: @from_fixed_int32_t__to_gnu_int32_t(
+// CHECK-NEXT:  entry:
+// CHECK-NEXT:    [[TYPE:%.*]] = alloca <16 x i32>, align 16
+// CHECK-NEXT:    [[TMP0:%.*]] = bitcast <16 x i32>* [[TYPE]] to <vscale x 4 x i32>*
+// CHECK-NEXT:    store <vscale x 4 x i32> [[TYPE_COERCE:%.*]], <vscale x 4 x i32>* [[TMP0]], align 16
+// CHECK-NEXT:    [[TYPE1:%.*]] = load <16 x i32>, <16 x i32>* [[TYPE]], align 16, [[TBAA2]]
+// CHECK-NEXT:    store <16 x i32> [[TYPE1]], <16 x i32>* [[AGG_RESULT:%.*]], align 16, [[TBAA2]]
+// CHECK-NEXT:    ret void
+//
+gnu_int32_t from_fixed_int32_t__to_gnu_int32_t(fixed_int32_t type) {
+  return type;
+}

clang/test/Sema/attr-arm-sve-vector-bits.c

-// RUN: %clang_cc1 -triple aarch64-none-linux-gnu -target-feature +sve -target-feature +bf16 -fsyntax-only -verify -msve-vector-bits=128 -fallow-half-arguments-and-returns %s
-// RUN: %clang_cc1 -triple aarch64-none-linux-gnu -target-feature +sve -target-feature +bf16 -fsyntax-only -verify -msve-vector-bits=256 -fallow-half-arguments-and-returns %s
-// RUN: %clang_cc1 -triple aarch64-none-linux-gnu -target-feature +sve -target-feature +bf16 -fsyntax-only -verify -msve-vector-bits=512 -fallow-half-arguments-and-returns %s
-// RUN: %clang_cc1 -triple aarch64-none-linux-gnu -target-feature +sve -target-feature +bf16 -fsyntax-only -verify -msve-vector-bits=1024 -fallow-half-arguments-and-returns %s
-// RUN: %clang_cc1 -triple aarch64-none-linux-gnu -target-feature +sve -target-feature +bf16 -fsyntax-only -verify -msve-vector-bits=2048 -fallow-half-arguments-and-returns %s
+// RUN: %clang_cc1 -triple aarch64-none-linux-gnu -target-feature +sve -target-feature +bf16 -ffreestanding -fsyntax-only -verify -msve-vector-bits=128 -fallow-half-arguments-and-returns %s
+// RUN: %clang_cc1 -triple aarch64-none-linux-gnu -target-feature +sve -target-feature +bf16 -ffreestanding -fsyntax-only -verify -msve-vector-bits=256 -fallow-half-arguments-and-returns %s
+// RUN: %clang_cc1 -triple aarch64-none-linux-gnu -target-feature +sve -target-feature +bf16 -ffreestanding -fsyntax-only -verify -msve-vector-bits=512 -fallow-half-arguments-and-returns %s
+// RUN: %clang_cc1 -triple aarch64-none-linux-gnu -target-feature +sve -target-feature +bf16 -ffreestanding -fsyntax-only -verify -msve-vector-bits=1024 -fallow-half-arguments-and-returns %s
+// RUN: %clang_cc1 -triple aarch64-none-linux-gnu -target-feature +sve -target-feature +bf16 -ffreestanding -fsyntax-only -verify -msve-vector-bits=2048 -fallow-half-arguments-and-returns %s
+
+#include <stdint.h>
 
 #define N __ARM_FEATURE_SVE_BITS
 
+typedef __fp16 float16_t;
+typedef float float32_t;
+typedef double float64_t;
 typedef __SVInt8_t svint8_t;
 typedef __SVInt16_t svint16_t;
 typedef __SVInt32_t svint32_t;
 typedef __SVInt64_t svint64_t;
 typedef __SVUint8_t svuint8_t;
 typedef __SVUint16_t svuint16_t;
 typedef __SVUint32_t svuint32_t;
 typedef __SVUint64_t svuint64_t;
 typedef __SVFloat16_t svfloat16_t;
 typedef __SVFloat32_t svfloat32_t;
 typedef __SVFloat64_t svfloat64_t;
 
 #if defined(__ARM_FEATURE_SVE_BF16)
+typedef __bf16 bfloat16_t;
 typedef __SVBFloat16_t svbfloat16_t;
 #endif
 
 typedef __SVBool_t svbool_t;
 
 // Define valid fixed-width SVE types
 typedef svint8_t fixed_int8_t __attribute__((arm_sve_vector_bits(N)));
 typedef svint16_t fixed_int16_t __attribute__((arm_sve_vector_bits(N)));
 typedef svint32_t fixed_int32_t __attribute__((arm_sve_vector_bits(N)));
 typedef svint64_t fixed_int64_t __attribute__((arm_sve_vector_bits(N)));
 
 typedef svuint8_t fixed_uint8_t __attribute__((arm_sve_vector_bits(N)));
 typedef svuint16_t fixed_uint16_t __attribute__((arm_sve_vector_bits(N)));
 typedef svuint32_t fixed_uint32_t __attribute__((arm_sve_vector_bits(N)));
 typedef svuint64_t fixed_uint64_t __attribute__((arm_sve_vector_bits(N)));
 
 typedef svfloat16_t fixed_float16_t __attribute__((arm_sve_vector_bits(N)));
 typedef svfloat32_t fixed_float32_t __attribute__((arm_sve_vector_bits(N)));
 typedef svfloat64_t fixed_float64_t __attribute__((arm_sve_vector_bits(N)));
 
 typedef svbfloat16_t fixed_bfloat16_t __attribute__((arm_sve_vector_bits(N)));
 
 typedef svbool_t fixed_bool_t __attribute__((arm_sve_vector_bits(N)));
 
+// GNU vector types
+typedef int8_t gnu_int8_t __attribute__((vector_size(N / 8)));
+typedef int16_t gnu_int16_t __attribute__((vector_size(N / 8)));
+typedef int32_t gnu_int32_t __attribute__((vector_size(N / 8)));
+typedef int64_t gnu_int64_t __attribute__((vector_size(N / 8)));
+
+typedef uint8_t gnu_uint8_t __attribute__((vector_size(N / 8)));
+typedef uint16_t gnu_uint16_t __attribute__((vector_size(N / 8)));
+typedef uint32_t gnu_uint32_t __attribute__((vector_size(N / 8)));
+typedef uint64_t gnu_uint64_t __attribute__((vector_size(N / 8)));
+
+typedef float16_t gnu_float16_t __attribute__((vector_size(N / 8)));
+typedef float32_t gnu_float32_t __attribute__((vector_size(N / 8)));
+typedef float64_t gnu_float64_t __attribute__((vector_size(N / 8)));
+
+typedef bfloat16_t gnu_bfloat16_t __attribute__((vector_size(N / 8)));
+
 // Attribute must have a single argument
 typedef svint8_t no_argument __attribute__((arm_sve_vector_bits));         // expected-error {{'arm_sve_vector_bits' attribute takes one argument}}
 typedef svint8_t two_arguments __attribute__((arm_sve_vector_bits(2, 4))); // expected-error {{'arm_sve_vector_bits' attribute takes one argument}}
 
 // The number of SVE vector bits must be an integer constant expression
 typedef svint8_t non_int_size1 __attribute__((arm_sve_vector_bits(2.0)));   // expected-error {{'arm_sve_vector_bits' attribute requires an integer constant}}
 typedef svint8_t non_int_size2 __attribute__((arm_sve_vector_bits("256"))); // expected-error {{'arm_sve_vector_bits' attribute requires an integer constant}}
 

 union union_int64 { fixed_int64_t x, y[5]; };
 union union_float64 { fixed_float64_t x, y[5]; };
 union union_bfloat16 { fixed_bfloat16_t x, y[5]; };
 union union_bool { fixed_bool_t x, y[5]; };
 
 // --------------------------------------------------------------------------//
 // Implicit casts
 
-#define TEST_CAST(TYPE)                                          \
-  sv##TYPE##_t to_sv##TYPE##_t(fixed_##TYPE##_t x) { return x; } \
-  fixed_##TYPE##_t from_sv##TYPE##_t(sv##TYPE##_t x) { return x; }
-
-TEST_CAST(int8)
-TEST_CAST(int16)
-TEST_CAST(int32)
-TEST_CAST(int64)
-TEST_CAST(uint8)
-TEST_CAST(uint16)
-TEST_CAST(uint32)
-TEST_CAST(uint64)
-TEST_CAST(float16)
-TEST_CAST(float32)
-TEST_CAST(float64)
-TEST_CAST(bfloat16)
-TEST_CAST(bool)
+#define TEST_CAST_COMMON(TYPE)                                              \
+  sv##TYPE##_t to_sv##TYPE##_t_from_fixed(fixed_##TYPE##_t x) { return x; } \
+  fixed_##TYPE##_t from_sv##TYPE##_t_to_fixed(sv##TYPE##_t x) { return x; }
+
+#define TEST_CAST_GNU(PREFIX, TYPE)                                                          \
+  gnu_##TYPE##_t to_gnu_##TYPE##_t_from_##PREFIX##TYPE##_t(PREFIX##TYPE##_t x) { return x; } \
+  PREFIX##TYPE##_t from_gnu_##TYPE##_t_to_##PREFIX##TYPE##_t(gnu_##TYPE##_t x) { return x; }
+
+#define TEST_CAST_VECTOR(TYPE) \
+  TEST_CAST_COMMON(TYPE)       \
+  TEST_CAST_GNU(sv, TYPE)      \
+  TEST_CAST_GNU(fixed_, TYPE)
+
+TEST_CAST_VECTOR(int8)
+TEST_CAST_VECTOR(int16)
+TEST_CAST_VECTOR(int32)
+TEST_CAST_VECTOR(int64)
+TEST_CAST_VECTOR(uint8)
+TEST_CAST_VECTOR(uint16)
+TEST_CAST_VECTOR(uint32)
+TEST_CAST_VECTOR(uint64)
+TEST_CAST_VECTOR(float16)
+TEST_CAST_VECTOR(float32)
+TEST_CAST_VECTOR(float64)
+TEST_CAST_VECTOR(bfloat16)
+TEST_CAST_COMMON(bool)
 
 // Test the implicit conversion only applies to valid types
 fixed_int8_t to_fixed_int8_t__from_svuint8_t(svuint8_t x) { return x; } // expected-error-re {{returning 'svuint8_t' (aka '__SVUint8_t') from a function with incompatible result type 'fixed_int8_t' (vector of {{[0-9]+}} 'signed char' values)}}
 fixed_bool_t to_fixed_bool_t__from_svint32_t(svint32_t x) { return x; } // expected-error-re {{returning 'svint32_t' (aka '__SVInt32_t') from a function with incompatible result type 'fixed_bool_t' (vector of {{[0-9]+}} 'unsigned char' values)}}
 
+svint64_t to_svint64_t__from_gnu_int32_t(gnu_int32_t x) { return x; } // expected-error-re {{returning 'gnu_int32_t' (vector of {{[0-9]+}} 'int32_t' values) from a function with incompatible result type 'svint64_t' (aka '__SVInt64_t')}}
+gnu_int32_t from_svint64_t__to_gnu_int32_t(svint64_t x) { return x; } // expected-error-re {{returning 'svint64_t' (aka '__SVInt64_t') from a function with incompatible result type 'gnu_int32_t' (vector of {{[0-9]+}} 'int32_t' values)}}
+
+// Test implicit conversion between SVE and GNU vector is invalid when
+// __ARM_FEATURE_SVE_BITS != N
+#if defined(__ARM_FEATURE_SVE_BITS) && __ARM_FEATURE_SVE_BITS == 512
+typedef int32_t int4 __attribute__((vector_size(16)));
+svint32_t badcast(int4 x) { return x; } // expected-error {{returning 'int4' (vector of 4 'int32_t' values) from a function with incompatible result type 'svint32_t' (aka '__SVInt32_t')}}
+#endif
+
 // Test conversion between predicate and uint8 is invalid, both have the same
 // memory representation.
 fixed_bool_t to_fixed_bool_t__from_svuint8_t(svuint8_t x) { return x; } // expected-error-re {{returning 'svuint8_t' (aka '__SVUint8_t') from a function with incompatible result type 'fixed_bool_t' (vector of {{[0-9]+}} 'unsigned char' values)}}
 
-// Test the implicit conversion only applies to fixed-length types
-typedef signed int vSInt32 __attribute__((__vector_size__(16)));
-svint32_t to_svint32_t_from_gnut(vSInt32 x) { return x; } // expected-error-re {{returning 'vSInt32' (vector of {{[0-9]+}} 'int' values) from a function with incompatible result type 'svint32_t' (aka '__SVInt32_t')}}
-
-vSInt32 to_gnut_from_svint32_t(svint32_t x) { return x; } // expected-error-re {{returning 'svint32_t' (aka '__SVInt32_t') from a function with incompatible result type 'vSInt32' (vector of {{[0-9]+}} 'int' values)}}
-
 // --------------------------------------------------------------------------//
 // Test the scalable and fixed-length types can be used interchangeably
 
 svint32_t __attribute__((overloadable)) svfunc(svint32_t op1, svint32_t op2);
 svfloat64_t __attribute__((overloadable)) svfunc(svfloat64_t op1, svfloat64_t op2);
 svbool_t __attribute__((overloadable)) svfunc(svbool_t op1, svbool_t op2);
 
 #define TEST_CALL(TYPE)                                              \

clang/test/SemaCXX/attr-arm-sve-vector-bits.cpp

-// RUN: %clang_cc1 -triple aarch64-none-linux-gnu -target-feature +sve -target-feature +bf16 -fsyntax-only -verify -std=c++11 -msve-vector-bits=512 -fallow-half-arguments-and-returns %s
+// RUN: %clang_cc1 -triple aarch64-none-linux-gnu -target-feature +sve -target-feature +bf16 -ffreestanding -fsyntax-only -verify -std=c++11 -msve-vector-bits=512 -fallow-half-arguments-and-returns %s
 // expected-no-diagnostics
 
+#include <stdint.h>
+
 #define N __ARM_FEATURE_SVE_BITS
 
 typedef __SVInt8_t svint8_t;
 typedef svint8_t fixed_int8_t __attribute__((arm_sve_vector_bits(N)));
+typedef int8_t gnu_int8_t __attribute__((vector_size(N / 8)));
 
 template<typename T> struct S { T var; };
 
 S<fixed_int8_t> s;
 
+// Test implicit casts between VLA and VLS vectors
 svint8_t to_svint8_t(fixed_int8_t x) { return x; }
 fixed_int8_t from_svint8_t(svint8_t x) { return x; }
+
+// Test implicit casts between GNU and VLA vectors
+svint8_t to_svint8_t__from_gnu_int8_t(gnu_int8_t x) { return x; }
+gnu_int8_t from_svint8_t__to_gnu_int8_t(svint8_t x) { return x; }
+
+// Test implicit casts between GNU and VLS vectors
+fixed_int8_t to_fixed_int8_t__from_gnu_int8_t(gnu_int8_t x) { return x; }
+gnu_int8_t from_fixed_int8_t__to_gnu_int8_t(fixed_int8_t x) { return x; }