Withdrawn: 8309266: C2: assert(final_con == (jlong)final_int) failed: final value should be integer

[Daohan Qu]

On Wed, 7 Jun 2023 12:33:48 GMT, Daohan Qu <duke at openjdk.org> wrote:

> This patch should fix [JDK-8309266](https://bugs.openjdk.org/browse/JDK-8309266). A `jtreg` test is also added. I'd appreciate any comments and reviews. Thanks in advance!
> 
> ## Problem Analysis
> 
> For the following program,
> 
> public class Test {
> 
>     static boolean flag;
> 
>     public static void main(String[] args) {
>         for (int i = 0; i < 10000; i++) {
>             flag = !flag;
>             test();
>         }
>     }
> 
>     public static void test() {
>         int limit = flag ? Integer.MAX_VALUE : 1000;
> 
>         int i = 0;
>         while (i < limit) {
>             i += 3;
>             if (flag) {
>                 return;
>             }
>         }
>     }
> }
> 
> A `LoopLimitNode` will be generated and its `Limit` input is a `PhiNode`, as depicted in the following picture.
> 
> <img width="384" alt="phi_as_limit" src="https://github.com/openjdk/jdk/assets/18374295/c561bb09-9789-45c2-8fa8-5bc690ea8046">
> 
> During `PhaseCCP`, the `LoopLimitNode::Value()` tries to calculate the constant final value:
> https://github.com/openjdk/jdk/blob/16ebf47fe3b0fac7b67acfa589a26abf8843306b/src/hotspot/share/opto/loopnode.cpp#L2289-L2301
> 
> The problem is that the assertion in `line 2299` could fail during CCP though it must hold true at the end of CCP. Here is the reason: `PhaseCCP` initializes all nodes with the type `TOP` and iterates in an "arbitrary" order. The following order may happen:
> 
> 28 IfTrue => 34 Region => 36 Phi => 195 LoopLimit => ... => 29 IfFalse
> 
> 1. In `ProjNode::Value()` (`IfTrue` inherits it), the type of `IfTrue` is set to `Type::CONTROL`
> https://github.com/openjdk/jdk/blob/fa791119f0b73cd1e110d6a62d3bed58fee5740a/src/hotspot/share/opto/multnode.cpp#L168-L171
> 
> 2. In `PhiNode::Value()`, only `28 IfTrue`'s correspondence `33 ConI` gets merged (as `29 IfFalse` has not been dealt with yet), then it has a value of `int:max`.
> https://github.com/openjdk/jdk/blob/fa791119f0b73cd1e110d6a62d3bed58fee5740a/src/hotspot/share/opto/cfgnode.cpp#L1269-L1277
> 
> 3. In `LoopLimitNode::Value()`, it finds its `Limit` input `36 Phi` is constant, which triggers the assertion, and the assertion fails since the final value calculated from that constant limit (`int:max`) overflows.
> 
> ## Solution
> Move the overflow check to the end of CCP, where it must not fail.

This pull request has been closed without being integrated.

-------------

PR: https://git.openjdk.org/jdk/pull/14353