Comments about JDK-8213473: Replace testB_mem_imm matcher with testUB_mem_imm
rkennke at redhat.com
Fri Nov 16 14:33:18 UTC 2018
So either we reinstate the testB pattern, or we make the conversion
check for sign-extended mask too? Not sure if the latter would be 100%
> The current fix  for JDK-8213473  replaces 'testB_mem_imm' with
> 'testUB_mem_imm' in 'x86_64.ad' which is fine for unsigned bytes, for
> if ((flags & 0x80) != 0) ...
> But per JLS §5.6.2 & §5.1.2, if we have something like :
> if ((flags & (byte)0x80) != 0) ...
> the mask is 32-bit sign-extended and 'LoadB' isn't converted to
> 'LoadUB' in 'AndINode::Ideal'  which is fine.
> Unfortunately 'testUB_mem_imm' won't be matched in this case, so I
> guess we'd need both 'testB_mem_imm' & 'testUB_mem_imm' patterns.
> If we all agree, I can create a JBS issue and send out a RFR for this?
>  http://hg.openjdk.java.net/jdk/jdk/rev/656d2f222b42
>  https://bugs.openjdk.java.net/browse/JDK-8213473
>  http://hg.openjdk.java.net/jdk/jdk/file/74109912c738/src/jdk.charsets/share/classes/sun/nio/cs/ext/ISO2022_CN.java#l165
>  http://hg.openjdk.java.net/jdk/jdk/file/74109912c738/src/hotspot/share/opto/mulnode.cpp#l493
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