RFR: 8267212: test/jdk/java/util/Collections/FindSubList.java debug build intermittent crash with "no reachable node should have no use"

[Hui Shi]

… crash with "no reachable node should have no use"

Please help reivew this fix.

StrIntrinsicNode::Ideal uses Node::set_req to replace memory input, old memory input might have 0 use, but not added into PhaseGVN worklist. Using set_req_X to ensure add 0 out old memory input node into PhaseGVN worklist.

Find other two similar problemtic code in LoadNode::Ideal.

Tier1/2/3 pass with release/fastdebug build.
test/jdk/java/util/Collections/FindSubList.java doesn't fail in 100 runs (before fix 2/3 failure in 10 runs).

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Commit messages:
 - 8267212: test/jdk/java/util/Collections/FindSubList.java intermittent crash with "no reachable node should have no use"

Changes: https://git.openjdk.java.net/jdk/pull/4055/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4055&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8267212
  Stats: 3 lines in 2 files changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4055.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4055/head:pull/4055

PR: https://git.openjdk.java.net/jdk/pull/4055