RFR: 8263352: assert(use == polladr) failed: the use should be a safepoint polling

[Roland Westrelin]

On Thu, 18 Mar 2021 18:20:59 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

> I have question for @rwestrel who did strip mining. Looking on nodes I see:
> 
> ```
>  1247  CountedLoop  ===  1247  1246  794  [[ 1247  788  741  738  781  1242 ]] inner stride: 1  strip mined !orig=[1237],[731] !jvms: ComponentSampleModel::<init> @ bci:147 (line 162)
>  1242  CountedLoopEnd  ===  1247  1241  [[ 1243  794 ]] [lt] P=0.646827, C=6564.000000 !orig=[793] !jvms: ComponentSampleModel::<init> @ bci:144 (line 161)
>  1243  IfFalse  ===  1242  [[ 1248 ]] #0 !orig=795 !jvms: ComponentSampleModel::<init> @ bci:144 (line 161)
> 
>  788  LoadP  ===  1247  659  787  [[ 1248 ]]  @rawptr:BotPTR, idx=Raw; #rawptr:BotPTR (does not depend only on test) !jvms: ComponentSampleModel::<init> @ bci:158 (line 161)
>  1248  SafePoint  ===  1243  1  784  1  1  788  10  1  1  1  1  1  1  782  [[ 1244 ]]  SafePoint  !orig=783 !jvms: ComponentSampleModel::<init> @ bci:158 (line 161)
> ```
> 
> So why Poll's LoadP node's control edge is not the same as SafePoint's control edge? Why it points to inner loop head?
> If we adjust LoadP's control edge to the same node as Safepoint (exit from inner loop), we would not need this special case in match_fill_loop().

That makes sense but needs to be done explicitly:
diff --git a/src/hotspot/share/opto/loopnode.cpp b/src/hotspot/share/opto/loopnode.cpp
index bf5a685960c..42e5b940dc5 100644
--- a/src/hotspot/share/opto/loopnode.cpp
+++ b/src/hotspot/share/opto/loopnode.cpp
@@ -1636,6 +1636,13 @@ bool PhaseIdealLoop::is_counted_loop(Node* x, IdealLoopTree*&loop, BasicType iv_
         Node* sfpt = sfpt2->clone();
         sfpt->set_req(0, iffalse);
         outer_le->set_req(0, sfpt);
+        Node* polladdr = sfpt->in(TypeFunc::Parms)->clone();
+        assert(polladdr->is_Load(), "");
+        Node* new_polladdr = polladdr->clone();
+        new_polladdr->set_req(0, iffalse);
+        _igvn.register_new_node_with_optimizer(new_polladdr, polladdr);
+        set_ctrl(new_polladdr, iffalse);
+        sfpt->set_req(TypeFunc::Parms, new_polladdr);
         // When this code runs, loop bodies have not yet been populated.
         const bool body_populated = false;
         register_control(sfpt, outer_ilt, iffalse, body_populated);

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PR: https://git.openjdk.java.net/jdk/pull/3061