8361037: [ubsan] compiler/c2/irTests/TestFloat16ScalarOperations division by 0

Reviewed-by: mhaessig, sviswanathan

Author: Jatin Bhateja

src/hotspot/share/opto/divnode.cpp

@@ -825,6 +825,29 @@ const Type* DivHFNode::Value(PhaseGVN* phase) const {
 
   if (t1->base() == Type::HalfFloatCon &&
       t2->base() == Type::HalfFloatCon)  {
+    // IEEE 754 floating point comparison treats 0.0 and -0.0 as equals.
+
+    // Division of a zero by a zero results in NaN.
+    if (t1->getf() == 0.0f && t2->getf() == 0.0f) {
+      return TypeH::make(NAN);
+    }
+
+    // As per C++ standard section 7.6.5 (expr.mul), behavior is undefined only if
+    // the second operand is 0.0. In all other situations, we can expect a standard-compliant
+    // C++ compiler to generate code following IEEE 754 semantics.
+    if (t2->getf() == 0.0) {
+      // If either operand is NaN, the result is NaN
+      if (g_isnan(t1->getf())) {
+        return TypeH::make(NAN);
+      } else {
+        // Division of a nonzero finite value by a zero results in a signed infinity. Also,
+        // division of an infinity by a finite value results in a signed infinity.
+        bool res_sign_neg = (jint_cast(t1->getf()) < 0) ^ (jint_cast(t2->getf()) < 0);
+        const TypeF* res = res_sign_neg ? TypeF::NEG_INF : TypeF::POS_INF;
+        return TypeH::make(res->getf());
+      }
+    }
+
     return TypeH::make(t1->getf() / t2->getf());
   }