[ARM] PR66791: Replace builtins for signed vmul_n intrinsics

[Prathamesh Kulkarni via Gcc-patches]

Hi,
This patch replaces builtins with __a * __b for signed variants of
vmul_n intrinsics.
As discussed earlier, the patch has issue if __a * __b overflows, and
whether we wish to leave
that as UB.

Thanks,
Prathamesh

diff --git a/gcc/config/arm/arm_neon.h b/gcc/config/arm/arm_neon.h
index 41b596b5fc6..5928c25318b 100644
--- a/gcc/config/arm/arm_neon.h
+++ b/gcc/config/arm/arm_neon.h
@@ -8370,14 +8370,14 @@ __extension__ extern __inline int16x4_t
 __attribute__  ((__always_inline__, __gnu_inline__, __artificial__))
 vmul_n_s16 (int16x4_t __a, int16_t __b)
 {
-  return (int16x4_t)__builtin_neon_vmul_nv4hi (__a, (__builtin_neon_hi) __b);
+  return __a * __b;
 }
 
 __extension__ extern __inline int32x2_t
 __attribute__  ((__always_inline__, __gnu_inline__, __artificial__))
 vmul_n_s32 (int32x2_t __a, int32_t __b)
 {
-  return (int32x2_t)__builtin_neon_vmul_nv2si (__a, (__builtin_neon_si) __b);
+  return __a * __b;
 }
 
 __extension__ extern __inline float32x2_t
@@ -8409,14 +8409,14 @@ __extension__ extern __inline int16x8_t
 __attribute__  ((__always_inline__, __gnu_inline__, __artificial__))
 vmulq_n_s16 (int16x8_t __a, int16_t __b)
 {
-  return (int16x8_t)__builtin_neon_vmul_nv8hi (__a, (__builtin_neon_hi) __b);
+  return __a * __b;
 }
 
 __extension__ extern __inline int32x4_t
 __attribute__  ((__always_inline__, __gnu_inline__, __artificial__))
 vmulq_n_s32 (int32x4_t __a, int32_t __b)
 {
-  return (int32x4_t)__builtin_neon_vmul_nv4si (__a, (__builtin_neon_si) __b);
+  return __a * __b;
 }
 
 __extension__ extern __inline float32x4_t