RFR: 8370200: Crash: assert(outer->outcnt() >= phis + 2 - be_loads && outer->outcnt() <= phis + 2 + stores + 1) failed: only phis [v3]

[Daniel Lundén]

On Thu, 11 Dec 2025 09:48:22 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 with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains eight additional commits since the last revision:
> 
>  - review
>  - Merge branch 'master' into JDK-8370200
>  - Update test/hotspot/jtreg/compiler/loopstripmining/TestMismatchedMemoryPhis.java
>    
>    Co-authored-by: Roberto Castañeda Lozano <robcasloz at users.noreply.github.com>
>  - Update test/hotspot/jtreg/compiler/loopstripmining/TestMismatchedMemoryPhis.java
>    
>    Co-authored-by: Roberto Castañeda Lozano <robcasloz at users.noreply.github.com>
>  - more
>  - test
>  - more
>  - fix

Looks good @rwestrel! A few very minor suggestions.

src/hotspot/share/opto/cfgnode.cpp line 2689:

> 2687:   // doesn't happen.
> 2688:   // Look for non bottom Phis that should be transformed and enqueue them for igvn so PhiNode::Identity executes for
> 2689:   // them.

Suggestion:

  // PhiNode::Identity replaces a non-bottom memory phi with a bottom memory phi with the same inputs, if it exists.
  // If the bottom memory phi's inputs are changed (so it can now replace the non-bottom memory phi) or if it's created
  // only after the non-bottom memory phi is processed by igvn, PhiNode::Identity doesn't run and the transformation
  // doesn't happen.
  // Look for non-bottom Phis that should be transformed and enqueue them for igvn so that PhiNode::Identity executes for
  // them.

src/hotspot/share/opto/node.cpp line 2898:

> 2896: }
> 2897: 
> 2898: 

Suggestion:

test/hotspot/jtreg/compiler/loopstripmining/TestMismatchedMemoryPhis.java line 44:

> 42:         int i, i1, i15 = 4, i16 = 4;
> 43:         for (i = 1; i < 7; ++i) {
> 44:            l = i;

Suggestion:

            l = i;

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

Marked as reviewed by dlunden (Committer).

PR Review: https://git.openjdk.org/jdk/pull/28677#pullrequestreview-3566848963
PR Review Comment: https://git.openjdk.org/jdk/pull/28677#discussion_r2610119032
PR Review Comment: https://git.openjdk.org/jdk/pull/28677#discussion_r2610122033
PR Review Comment: https://git.openjdk.org/jdk/pull/28677#discussion_r2610121611