review(S): 7058510: multinewarray with 6 dimensions uncommon traps in server compiler

[John Rose]

On Jul 1, 2011, at 1:26 PM, Vladimir Kozlov wrote:

> Wrap new java dimension allocation into PreserveReexecuteState scope and restore stack.

Is this in case the initial allocation deoptimizes (due to some external event)?  I suppose that should be tested with DeoptimizeALot.

Igor, the extraction from the dope array bothers me:
+   jint *j_dims = (jint*)dims->base(T_INT);
+   jint *c_dims = NEW_RESOURCE_ARRAY(jint, len);
+   memcpy(c_dims, j_dims, sizeof(jint)*len);

It is correct, but I'd rather see more use of Hotspot machinery, with stronger typing:
+   jint *j_dims = typeArrayOop(dims)->int_at_addr(0);
+   jint *c_dims = NEW_RESOURCE_ARRAY(jint, len);
+   Copy::conjoint_jints_atomic(c_dims, j_dims, sizeof(jint)*len);

Note that Copy::* strongly outnumbers memcpy in the opto directory.  The distinction is mostly stylistic, but Copy:: is more strongly typed in this case.

(In other uses, Copy:: is more explicit and careful about some of the things we need to care about, such as overlaps and word-tearing.)

Also, use is_typeArray instead of is_array in the previous assert.  That will make the cast to typeArrayOop safe.

-- John