[11u] RFR (XS) 8259049: Uninitialized variable after JDK-8257513

[Aleksey Shipilev]

Original bug:
   https://bugs.openjdk.java.net/browse/JDK-8259049
   https://git.openjdk.java.net/jdk/commit/9f151649

This is a trivial follow-up for JDK-8257513 backport. Since the original code was moved from 
compile.cpp (as in JDK-8257513 as well), it does not apply cleanly.

11u variant:

diff -r ac1c8fae8707 src/hotspot/share/opto/compile.cpp
--- a/src/hotspot/share/opto/compile.cpp        Mon Dec 21 08:06:48 2020 +0000
+++ b/src/hotspot/share/opto/compile.cpp        Wed Jan 06 19:43:11 2021 +0100
@@ -4177,11 +4177,11 @@
        }
        assert((constant_addr - _masm.code()->consts()->start()) == con.offset(),
               "must be: %d == %d", (int)(constant_addr - _masm.code()->consts()->start()), 
(int)(con.offset()));

        // Expand jump-table
-      address last_addr;
+      address last_addr = NULL;
        for (uint j = 1; j < n->outcnt(); j++) {
          last_addr = _masm.address_constant(dummy + j);
          if (last_addr == NULL) {
            return false;
          }

Testing: observing build warning before this patch, and no warning after

-- 
Thanks,
-Aleksey