testsuite: arm: require fp16 alternative hw for tests

Currently, it's assumed that arm_fp16_alternative_ok is enough to run
the tests, but arm_fp16_alternative_ok allows multilib override.  While
the test might link without trouble, execution will likely fail.
Add arm_fp16_alternative_hw to explicitly test that target can execute
fp16 instructions in alternative form.

Below tests are known to fail for
thumb/arch=armv7e-m+fp/cpu=cortex-m4/float-abi=hard/fpu=auto among other
targets.

gcc/ChangeLog:

	* doc/sourcebuild.texi (arm_fp16_alternative_hw): Document.
	(arm_neon_fp16_hw): Add reference to arm_neon_fp16_ok.

gcc/testsuite/ChangeLog:

	* g++.dg/ext/arm-fp16/arm-fp16-ops-3.C: Require effective target
	arm_fp16_alternative_hw instead of arm_fp16_alternative_ok.
	* g++.dg/ext/arm-fp16/arm-fp16-ops-4.C: Likewise.
	* gcc.dg/torture/arm-fp16-int-convert-alt.c: Likewise.
	* gcc.dg/torture/arm-fp16-ops-3.c: Likewise.
	* gcc.dg/torture/arm-fp16-ops-4.c: Likewise.
	* lib/target-supports.exp (arm_fp16_alternative_hw): New proc.

Signed-off-by: Torbjörn SVENSSON <torbjorn.svensson@foss.st.com>
diff --git a/gcc/doc/sourcebuild.texi b/gcc/doc/sourcebuild.texi
index 7b59cf8..31e0552 100644
--- a/gcc/doc/sourcebuild.texi
+++ b/gcc/doc/sourcebuild.texi
@@ -2119,12 +2119,17 @@
 
 @item arm_neon_fp16_hw
 Test system supports executing Neon half-precision float instructions.
-(Implies previous.)
+(Implies @code(arm_neon_fp16_ok).)
 
 @item arm_fp16_alternative_ok
 ARM target supports the ARM FP16 alternative format.  Some multilibs
 may be incompatible with the options needed.
 
+@item arm_fp16_alternative_hw
+Test system supports executing VFP half-precision floating-point
+instructions in the ARM FP16 alternative format.  (Implies
+@code(arm_fp16_alternative_ok).)
+
 @item arm_fp16_none_ok
 ARM target supports specifying none as the ARM FP16 format.
 
diff --git a/gcc/testsuite/g++.dg/ext/arm-fp16/arm-fp16-ops-3.C b/gcc/testsuite/g++.dg/ext/arm-fp16/arm-fp16-ops-3.C
index 5eceb30..839da72 100644
--- a/gcc/testsuite/g++.dg/ext/arm-fp16/arm-fp16-ops-3.C
+++ b/gcc/testsuite/g++.dg/ext/arm-fp16/arm-fp16-ops-3.C
@@ -1,6 +1,6 @@
 /* Test various operators on __fp16 and mixed __fp16/float operands.  */
 /* { dg-do run { target arm*-*-* } } */
-/* { dg-require-effective-target arm_fp16_alternative_ok } */
+/* { dg-require-effective-target arm_fp16_alternative_hw } */
 /* { dg-add-options arm_fp16_alternative } */
 
 #include "arm-fp16-ops.h"
diff --git a/gcc/testsuite/g++.dg/ext/arm-fp16/arm-fp16-ops-4.C b/gcc/testsuite/g++.dg/ext/arm-fp16/arm-fp16-ops-4.C
index d86019f..ec22e25 100644
--- a/gcc/testsuite/g++.dg/ext/arm-fp16/arm-fp16-ops-4.C
+++ b/gcc/testsuite/g++.dg/ext/arm-fp16/arm-fp16-ops-4.C
@@ -1,6 +1,6 @@
 /* Test various operators on __fp16 and mixed __fp16/float operands.  */
 /* { dg-do run { target arm*-*-* } } */
-/* { dg-require-effective-target arm_fp16_alternative_ok } */
+/* { dg-require-effective-target arm_fp16_alternative_hw } */
 /* { dg-options "-ffast-math" } */
 /* { dg-add-options arm_fp16_alternative } */
 
diff --git a/gcc/testsuite/gcc.dg/torture/arm-fp16-int-convert-alt.c b/gcc/testsuite/gcc.dg/torture/arm-fp16-int-convert-alt.c
index 42171d4..08eba10 100644
--- a/gcc/testsuite/gcc.dg/torture/arm-fp16-int-convert-alt.c
+++ b/gcc/testsuite/gcc.dg/torture/arm-fp16-int-convert-alt.c
@@ -1,6 +1,6 @@
 /* Test floating-point conversions.  Standard types and __fp16.  */
 /* { dg-do run { target arm*-*-* } } */
-/* { dg-require-effective-target arm_fp16_alternative_ok }
+/* { dg-require-effective-target arm_fp16_alternative_hw } */
 /* { dg-add-options arm_fp16_alternative } */
 
 #include "fp-int-convert.h"
diff --git a/gcc/testsuite/gcc.dg/torture/arm-fp16-ops-3.c b/gcc/testsuite/gcc.dg/torture/arm-fp16-ops-3.c
index 3f0aecf..839da72 100644
--- a/gcc/testsuite/gcc.dg/torture/arm-fp16-ops-3.c
+++ b/gcc/testsuite/gcc.dg/torture/arm-fp16-ops-3.c
@@ -1,6 +1,6 @@
 /* Test various operators on __fp16 and mixed __fp16/float operands.  */
 /* { dg-do run { target arm*-*-* } } */
-/* { dg-require-effective-target arm_fp16_alternative_ok }
+/* { dg-require-effective-target arm_fp16_alternative_hw } */
 /* { dg-add-options arm_fp16_alternative } */
 
 #include "arm-fp16-ops.h"
diff --git a/gcc/testsuite/gcc.dg/torture/arm-fp16-ops-4.c b/gcc/testsuite/gcc.dg/torture/arm-fp16-ops-4.c
index 846515b..ec22e25 100644
--- a/gcc/testsuite/gcc.dg/torture/arm-fp16-ops-4.c
+++ b/gcc/testsuite/gcc.dg/torture/arm-fp16-ops-4.c
@@ -1,6 +1,6 @@
 /* Test various operators on __fp16 and mixed __fp16/float operands.  */
 /* { dg-do run { target arm*-*-* } } */
-/* { dg-require-effective-target arm_fp16_alternative_ok }
+/* { dg-require-effective-target arm_fp16_alternative_hw } */
 /* { dg-options "-ffast-math" } */
 /* { dg-add-options arm_fp16_alternative } */
 
diff --git a/gcc/testsuite/lib/target-supports.exp b/gcc/testsuite/lib/target-supports.exp
index 57a6df4..ab6aab6 100644
--- a/gcc/testsuite/lib/target-supports.exp
+++ b/gcc/testsuite/lib/target-supports.exp
@@ -6085,6 +6085,29 @@
 		check_effective_target_arm_fp16_alternative_ok_nocache]
 }
 
+# Return 1 if the target supports executing FP16 alternative format
+# instructions selected by arm_fp16_alternative_ok.
+
+proc check_effective_target_arm_fp16_alternative_hw { } {
+    if { ! [check_effective_target_arm_fp16_alternative_ok] } {
+	return 0
+    }
+
+    global et_arm_fp16_alternative_flags
+    check_runtime arm_fp16_alternative_hw {
+	int
+	main (int argc, char **argv)
+	{
+	  __fp16 a = 1.0;
+	  float r;
+	  asm ("vcvtb.f32.f16 %0, %1"
+	       : "=w" (r) : "w" (a)
+	       : /* No clobbers.  */);
+	  return (r == 1.0) ? 0 : 1;
+	}
+    } "$et_arm_fp16_alternative_flags"
+}
+
 # Return 1 if this is an ARM target supports specifying the FP16 none
 # format.  Some multilibs may be incompatible with the options needed.