git: openjdk/jdk: 8257190: simplify PhaseIdealLoop constructors

[Jie Fu]

Changeset: ce496cbd
Author:    Xin Liu <xliu at openjdk.org>
Committer: Jie Fu <jiefu at openjdk.org>
Date:      2020-12-01 23:50:53 +0000
URL:       https://git.openjdk.java.net/jdk/commit/ce496cbd

8257190: simplify PhaseIdealLoop constructors

Currently, C2 has 3 private constructors of PhaseIdealLoop as follows. a-b are for verification. only c is for real loop optimizations.
a. PhaseIdealLoop( PhaseIterGVN &igvn)
b. PhaseIdealLoop(PhaseIterGVN &igvn, const PhaseIdealLoop *verify_me)
c. PhaseIdealLoop(PhaseIterGVN &igvn, LoopOptsMode mode)

I propose 3 changes to simplify them.
1. add assertion in the constructor c. C2 shouldn't use mode = LoopOptsVerify for it.
2. merge a and b into one constructor.
3. make the merged verification ctor only for debug builds.

Reviewed-by: thartmann, kvn

! src/hotspot/share/opto/loopnode.hpp