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List:       openjdk-hotspot-compiler-dev
Subject:    Re: RFR: 8276105: C2: Conv(D|F)2(I|L)Nodes::Ideal should handle rounding correctly
From:       Xin Liu <xliu () openjdk ! java ! net>
Date:       2021-10-29 23:16:21
Message-ID: UM7b9XHMkf2uM8xCTrEKzqVZcrKvvKXJFhMx8YM1zHg=.f4bd2ea3-7d89-430e-9106-aec0e0f3db93 () github ! com
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On Fri, 29 Oct 2021 16:38:11 GMT, Aleksey Shipilev <shade@openjdk.org> wrote:

> Happens now in master:
> 
> 
> $ CONF=linux-x86-server-fastdebug make run-test \
> TEST=compiler/loopopts/superword/CoLocatePack.java TEST_VM_OPTS="-XX:UseAVX=0 \
>                 -XX:UseSSE=0"
> ...
> 
> CompileCommand: compileonly compiler/loopopts/superword/CoLocatePack.test bool \
> compileonly = true 191 ConvF2L === _ 714 [[ 193 ]] !jvms: CoLocatePack::test @ \
> bci:30 (line 70) # To suppress the following error report, specify this argument
> # after -XX: or in .hotspotrc: SuppressErrorAt=/phaseX.cpp:1128
> #
> # A fatal error has been detected by the Java Runtime Environment:
> #
> # Internal Error (/home/shade/trunks/jdk/src/hotspot/share/opto/phaseX.cpp:1128), \
> pid=1717516, tid=1717532 # fatal error: modified node was not processed by \
> IGVN.transform_old() 
> 
> After JDK-8266950 (always `strictfp`), the paths in `Conv(D|F)2(I|L)Nodes::Ideal`-s \
> start to be taken more frequently to round float/double inputs when low SSE is \
> enabled. On those paths, we call `set_req` to rewire current node, but we still \
> return `NULL` from `::Ideal`. I believe that is incorrect, as per `node.cpp` \
> explanation: `NULL` indicates no graph change was done, and `this` should be \
> returned when modification happened. So GVN predictably barfs. 
> Additional testing:
> - [x] Linux x86_32 `tier1` with `-XX:UseAVX=0 -XX:UseSSE=0` (now pass)
> - [x] Linux x86_32 `tier1` default (still pass)
> - [x] Linux x86_64 `tier1` default

LGTM. 
Prior code style in ConvD2INode::Ideal is obscure. This patch also makes it look \
better.

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

PR: https://git.openjdk.java.net/jdk/pull/6176


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