RFR (M): 8063137: Never-taken branches should be pruned when GWT LambdaForms are shared
john.r.rose at oracle.com
Tue Jan 27 21:08:47 UTC 2015
Looking very good, thanks. Ship it!
Actually, can you insert a comment why the injected counts are not scaled? (Or perhaps they should be??)
Also, we may need a followup bug for the code with this comment:
// Look for the following shape: AndI (ProfileBoolean) (ConI 1))
Since profileBoolean returns a TypeInt::BOOL, the AndI with (ConI 1) should fold up.
So there's some work to do in MulNode, which may allow that special pattern match to go away.
But I don't want to divert the present bug by a possibly complex dive into fixing AndI::Ideal.
(Generally speaking, pattern matching should assume strong normalization of its inputs. Otherwise you end up duplicating pattern match code in many places, inconsistently. Funny one-off idiom checks like this are evidence of incomplete IR normalization. See http://en.wikipedia.org/wiki/Rewriting for some background on terms like "normalization" and "confluence" which are relevant to C2.)
On Jan 27, 2015, at 8:05 AM, Vladimir Ivanov <vladimir.x.ivanov at oracle.com> wrote:
> Thanks for the feedback, John!
> Updated webrev:
> - renamed MHI::profileBranch to MHI::profileBoolean, and ProfileBranchNode to ProfileBooleanNode;
> - restructured profile layout ( => false_cnt,  => true_cnt)
> - factored out profile injection in a separate function (has_injected_profile() in parse2.cpp)
> - ProfileBooleanNode stores true/false counts instead of taken/not_taken counts
> - matching from value counts to taken/not_taken happens in has_injected_profile();
> - added BoolTest::ne support
> - sharpened test for AndI case: now it checks AndI (ProfileBoolean) (ConI 1) shape
> Best regards,
> Vladimir Ivanov
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