ARM: fp16 Fix PR 67624 - Incorrect conversion of float Infinity to __fp16

[Richard Earnshaw]

This patch fixes the bug reported in PR67624 where a single-precision
infinity value was being incorrectly converted to a half-precision NaN
value.
Since we need to preserve the semantics of converting signaling NaNs to
quiet NaNs, we test explicitly for this case.

Built and tested on an arm-eabi cross.  Applied to trunk.


libgcc:
        PR libgcc/67624
        * config/arm/fp16.c (__gnu_f2h_internal): Handle infinity correctly.

gcc/testsuite:
        PR libgcc/67624
        * gcc.target/arm/fp16-inf.c: New test.


diff --git a/gcc/testsuite/gcc.target/arm/fp16-inf.c 
b/gcc/testsuite/gcc.target/arm/fp16-inf.c
new file mode 100644
index 0000000..ce5c197
--- /dev/null
+++ b/gcc/testsuite/gcc.target/arm/fp16-inf.c
@@ -0,0 +1,14 @@
+/* { dg-do run } */
+/* { dg-options "-O -mfp16-format=ieee" } */
+
+/* Conversion of infinity to __fp16 and back again should preserve the
+   value.  */
+volatile float f = __builtin_inf ();
+
+int main ()
+{
+  __fp16 h = f;
+  if (h != __builtin_inf ())
+    __builtin_abort ();
+  return 0;
+}
diff --git a/libgcc/config/arm/fp16.c b/libgcc/config/arm/fp16.c
index 86a6348..8eaae2b 100644
--- a/libgcc/config/arm/fp16.c
+++ b/libgcc/config/arm/fp16.c
@@ -35,9 +35,12 @@ __gnu_f2h_internal(unsigned int a, int ieee)
     {
       if (!ieee)
        return sign;
+      if (mantissa == 0)
+       return sign | 0x7c00;   /* Infinity.  */
+      /* Remaining cases are NaNs.  Convert SNaN to QNaN.  */
       return sign | 0x7e00 | (mantissa >> 13);
     }
-  
+
   if (aexp == 0 && mantissa == 0)
     return sign;
 
@@ -49,7 +52,7 @@ __gnu_f2h_internal(unsigned int a, int ieee)
     {
       mask = 0x00ffffff;
       if (aexp >= -25)
-        mask >>= 25 + aexp;
+       mask >>= 25 + aexp;
     }
   else
     mask = 0x00001fff;