RFR: 8370200: Crash: assert(outer->outcnt() >= phis + 2 - be_loads && outer->outcnt() <= phis + 2 + stores + 1) failed: only phis [v4]

[Emanuel Peter]

On Thu, 11 Dec 2025 15:46:40 GMT, Roland Westrelin <roland at openjdk.org> wrote:

>> The crash occurs because verification code expects the inner and outer
>> loop of a loop strip mining nest to have the same number of phis but,
>> in this case, the inner loop has one more memory phis than the outer
>> loop.
>> 
>> 1) After `OuterStripMinedLoopNode::adjust_strip_mined_loop`, inner and
>> outer loops have the same number of phis, as expected.
>> 
>> 
>>  309  MergeMem  === _ 1 306 1 1 284  [[ 429 ]]  { - - N284:instptr:java/lang/Throwable (java/io/Serializable):BotPTR+20,iid=bot [narrow] }  Memory: @ptr:BotPTR+bot, idx=Bot; !orig=205 !jvms: TestMismatchedMemoryPhis::mainTest @ bci:37 (line 49)
>> 
>>  248  OuterStripMinedLoop  === 248 321 247  [[ 248 249 428 429 430 ]] 
>>  429  Phi  === 248 309 205  [[ 93 ]]  #memory  Memory: @ptr:BotPTR+bot, idx=Bot; !orig=93 !jvms: TestMismatchedMemoryPhis::mainTest @ bci:37 (line 49)
>>  430  Phi  === 248 306 121  [[ 94 ]]  #memory  Memory: @instptr:TestMismatchedMemoryPhis:BotPTR+16,iid=bot, name=l, idx=4; !orig=94 !jvms: TestMismatchedMemoryPhis::mainTest @ bci:37 (line 49)
>> 
>>  249  CountedLoop  === 249 248 197  [[ 249 119 96 93 94 ]] inner stride: 1  strip mined !orig=[223],[91] !jvms: TestMismatchedMemoryPhis::mainTest @ bci:37 (line 49)
>>   93  Phi  === 249 429 205  [[ 117 97 ]]  #memory  Memory: @ptr:BotPTR+bot, idx=Bot; !jvms: TestMismatchedMemoryPhis::mainTest @ bci:37 (line 49)
>>   94  Phi  === 249 430 121  [[ 97 ]]  #memory  Memory: @instptr:TestMismatchedMemoryPhis:BotPTR+16,iid=bot, name=l, idx=4; !jvms: TestMismatchedMemoryPhis::mainTest @ bci:37 (line 49)
>> 
>> 
>> 2) Then `PhiNode::Ideal` runs for 429 and pushed the `MergeMem` 309
>> through the outer loop phi:
>> 
>> 
>>  248  OuterStripMinedLoop  === 248 321 247  [[ 248 249 428 429 430 444 446 ]] 
>>  430  Phi  === 248 306 121  [[ 94 ]]  #memory  Memory: @instptr:TestMismatchedMemoryPhis:BotPTR+16,iid=bot, name=l, idx=4; !orig=94 !jvms: TestMismatchedMemoryPhis::mainTest @ bci:37 (line 49)
>>  444  Phi  === 248 306 121  [[ 445 ]]  #memory  Memory: @ptr:BotPTR+bot, idx=Bot; !orig=429,93 !jvms: TestMismatchedMemoryPhis::mainTest @ bci:37 (line 49)
>>  446  Phi  === 248 284 170  [[ 445 ]]  #memory  Memory: @instptr:java/lang/Throwable (java/io/Serializable):BotPTR+20,iid=bot [narrow], name=detailMessage, idx=5; !orig=444,429,93 !jvms: TestMismatchedMemoryPhis::mainTest @ bci:37 (line 49)
>> 
>>  445  MergeMem  === _ 1 444 1 1 446  [[ 93 ]]  { - - N446:instptr:java/lang/Throwable (java/io/Serializable):BotPTR+20,iid=bot [narrow] }  Memory: @ptr:BotPTR+bot, idx...
>
> Roland Westrelin has updated the pull request incrementally with three additional commits since the last revision:
> 
>  - Update src/hotspot/share/opto/node.cpp
>    
>    Co-authored-by: Daniel Lundén <daniel.lunden at oracle.com>
>  - Update test/hotspot/jtreg/compiler/loopstripmining/TestMismatchedMemoryPhis.java
>    
>    Co-authored-by: Daniel Lundén <daniel.lunden at oracle.com>
>  - Update src/hotspot/share/opto/cfgnode.cpp
>    
>    Co-authored-by: Daniel Lundén <daniel.lunden at oracle.com>

src/hotspot/share/opto/cfgnode.cpp line 2701:

> 2699:       }
> 2700:     }
> 2701:   }

Another drive-by question:
You are refactoring / fixing existing optimizations:
Are there IR tests that cover the original optimization? How do we avoid that we lose optimizations here?

test/hotspot/jtreg/compiler/loopstripmining/TestMismatchedMemoryPhis.java line 34:

> 32:  *                   -XX:CompileCommand=compileonly,*TestMismatchedMemoryPhis*::mainTest -XX:-TieredCompilation
> 33:  *                   -Xcomp -XX:+StressIGVN -XX:+StressLoopPeeling -XX:PerMethodTrapLimit=0 TestMismatchedMemoryPhis
> 34:  * @run main TestMismatchedMemoryPhis

Suggestion:

 * @run main ${test.main.class}

Optional nits, drive-by stile 😬
Possible since a new JTREG version. Also: you test does not have a package.

test/hotspot/jtreg/compiler/loopstripmining/TestMismatchedMemoryPhis.java line 62:

> 60:         } catch (NullPointerException npe) {
> 61:             // Expected
> 62:         }

Could this exception be avoided, and still reproduce the bug?

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

PR Review Comment: https://git.openjdk.org/jdk/pull/28677#discussion_r2614168898
PR Review Comment: https://git.openjdk.org/jdk/pull/28677#discussion_r2614160478
PR Review Comment: https://git.openjdk.org/jdk/pull/28677#discussion_r2614162891