[GCC, Arm] Fix availability of FP16-FP64 conversion instructions

vcvtb.f16.f64 and vcvtb.f64.f16 were being made available even for FPUs that do
not support double precision.  This patch fixes that.

gcc/ChangeLog:
2019-03-08  Andre Vieira  <andre.simoesdiasvieira@arm.com>

	* config/arm/arm.h (TARGET_FP16_TO_DOUBLE): Add TARGET_VFP_DOUBLE
	requirement.

gcc/testsuite/ChangeLog:
2019-03-08  Andre Vieira  <andre.simoesdiasvieira@arm.com>

	* gcc.target/arm/f16_f64_conv_no_dp.c: New test.

From-SVN: r269499

gcc/ChangeLog

+2019-03-08  Andre Vieira  <andre.simoesdiasvieira@arm.com>
+
+	* config/arm/arm.h (TARGET_FP16_TO_DOUBLE): Add TARGET_VFP_DOUBLE
+	requirement.
+
 2019-03-08  Uroš Bizjak  <ubizjak@gmail.com>
 
 	PR target/68924

gcc/config/arm/arm.h

@@ -195,7 +195,7 @@ extern tree arm_fp16_type_node;
 /* FPU supports converting between HFmode and DFmode in a single hardware
    step.  */
 #define TARGET_FP16_TO_DOUBLE						\
-  (TARGET_HARD_FLOAT && (TARGET_FP16 && TARGET_VFP5))
+  (TARGET_HARD_FLOAT && TARGET_FP16 && TARGET_VFP5 && TARGET_VFP_DOUBLE)
 
 /* FPU supports fused-multiply-add operations.  */
 #define TARGET_FMA (bitmap_bit_p (arm_active_target.isa, isa_bit_vfpv4))

gcc/testsuite/ChangeLog

+2019-03-08  Andre Vieira  <andre.simoesdiasvieira@arm.com>
+
+	* gcc.target/arm/f16_f64_conv_no_dp.c: New test.
+
 2019-03-08  Uroš Bizjak  <ubizjak@gmail.com>
 
 	PR target/68924

gcc/testsuite/gcc.target/arm/f16_f64_conv_no_dp.c

+/* { dg-do compile } */
+/* { dg-skip-if "do not override fpu" { *-*-* } { "-mfpu=*" } { "-mfpu=fpv5-sp-d16" } } */
+/* { dg-skip-if "do not disable fpu" { *-*-* } { "-mfloat-abi=soft" } { * } } */
+/* { dg-skip-if "do not override fp16-format" { *-*-* } { "-mfp16-format=*" } { "-mfp16-format=ieee" } } */
+/* { dg-options "-O1 -mfpu=fpv5-sp-d16 -mfloat-abi=hard -mfp16-format=ieee" } */
+
+__fp16 foo (double a)
+{
+  return a;
+}
+
+double bar (__fp16 a)
+{
+  return a;
+}