Never hchange nan-hole to hole or hole to nan-hole.

test/mjsunit/regress/regress-convert-hole2.js

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+// Flags: --allow-natives-syntax --notrack-allocation-sites
 
-// Flags: --allow-natives-syntax
+// Test adding undefined from hole in double-holey to string.
+var a = [1.5, , 1.8];
 
-function f(i, b) {
-  var a = 0;
-  if (b) {
-    var c = 1 << i;
-    a = c + c;
-  }
-  var x = a >> 3;
-  return a;
+function f(a, i, l) {
+  var v = a[i];
+  return l + v;
 }
 
-f(1, false);
-f(1, true);
+assertEquals("test1.5", f(a, 0, "test"));
+assertEquals("test1.5", f(a, 0, "test"));
 %OptimizeFunctionOnNextCall(f);
-assertEquals((1 << 30) * 2, f(30, true));
+assertEquals("testundefined", f(a, 1, "test"));
 
-
-var global = 1;
-
-function f2(b) {
-  var a = 0;
+// Test double-hole going through a phi to a string-add.
+function f2(b, a1, a2) {
+  var v;
   if (b) {
-    a = global;
+    v = a1[0];
+  } else {
+    v = a2[0];
   }
-  var x = a >> 3;
-  return a;
+  x = v * 2;
+  return "test" + v + x;
 }
 
-f2(false);
-f2(true);
+f2(true, [1.4,1.8,,1.9], [1.4,1.8,,1.9]);
+f2(true, [1.4,1.8,,1.9], [1.4,1.8,,1.9]);
+f2(false, [1.4,1.8,,1.9], [1.4,1.8,,1.9]);
+f2(false, [1.4,1.8,,1.9], [1.4,1.8,,1.9]);
 %OptimizeFunctionOnNextCall(f2);
-global = 2.5;
-assertEquals(global, f2(true));
+assertEquals("testundefinedNaN", f2(false, [,1.8,,1.9], [,1.9,,1.9]));
+
+// Test converting smi-hole to double-hole.
+function t_smi(a) {
+  a[0] = 1.5;
+}
+
+t_smi([1,,3]);
+t_smi([1,,3]);
+t_smi([1,,3]);
+%OptimizeFunctionOnNextCall(t_smi);
+var ta = [1,,3];
+t_smi(ta);
+ta.__proto__ = [6,6,6];
+assertEquals([1.5,6,3], ta);
+
+// Test converting double-hole to tagged-hole.
+function t(b) {
+  b[1] = {};
+}
+
+t([1.4, 1.6,,1.8, NaN]);
+t([1.4, 1.6,,1.8, NaN]);
+%OptimizeFunctionOnNextCall(t);
+var a = [1.6, 1.8,,1.9, NaN];
+t(a);
+a.__proto__ = [6,6,6,6,6];
+assertEquals([1.6, {}, 6, 1.9, NaN], a);