Integrated: 8272968: AArch64: Remove redundant matching rules for commutative ops

[Fei Gao]

On Thu, 23 Sep 2021 03:29:44 GMT, Fei Gao <github.com+39403138+fg1417 at openjdk.org> wrote:

> Match rules for commutative operations mnegI/mnegL/smnegL might
> become redundant after function matchrule_clone_and_swap(),
> and hence can be reduced.
> 
> In adlc part, while parsing the contents of an instruction
> definition, function instr_parse always do the check
> for commutative operations with subtree operands, create
> clones and swap operands by function matchrule_clone_and_swap.
> It means that another operand-swapped and partially
> symmetrical match rule should be generated automatically for
> these commutative operations.
> 
> The pattern to construct mnegI, mnegL or smnegL consists of
> a subtraction with zero and then a multiplication. In function
> count_commutative_op, both mulI and mulL are recognized as
> commutative opcodes. Therefore, we need only one match rule
> to specify that a multipilication consists of a number and
> a subtraction with zero for these three instructions and the
> extra one can be deleted.
> 
> Take mnegL as an example.
> 
> Without my patch, four match rules will be created finally for
> instruction selection.
> 
> Two of them are created by ad files:
> 
> Match Rule 1:
> dst = MulL (SubL zero src1) src2
> ===>
> dst = mnegl src1 src2
> 
> Match Rule 2:
> dst = MulL src1 (SubL zero src2)
> ===>
> dst = mnegl src1 src2
> 
> The other two are automatically generated by function
> matchrule_clone_and_swap based on the two rules above:
> 
> Match Rule 3 (generated by match rule 1):
> dst = MulL src2 (SubL zero src1)
> ===>
> dst = mnegl src1 src2
> 
> Match Rule 4 (generated by match rule 2):
> dst = MulL (SubL zero src2) src1
> ===>
> dst = mnegl src1 src2
> 
> As mnegl is commutative, Rule 3 is equivalent to
> Rule 2, and Rule 1 is equivalent to Rule 4. Also, if we only
> keep the original Match Rule 1, as showed above, Rule 3 will
> be generated automatically later. In this way, Rule 2 and Rule 4
> are redundant and hence Rule 2 can be eliminated.
> 
> With my patch, Rule 2 is removed and Rule 4 won't be generated as well.
> Only Rule 1 and 3 are kept in the final rule chain. In my local release
> build, as redundant code got removed, the size of libjvm.so decreased
> from 23.30 MB to 23.27 MB, with a reduction of 33.11 KB(around 0.14%).

This pull request has now been integrated.

Changeset: c032186b
Author:    Fei Gao <Fei.Gao at arm.com>
Committer: Pengfei Li <pli at openjdk.org>
URL:       https://git.openjdk.java.net/jdk/commit/c032186b421c64b44397cb7aa101b40e5f93dfff
Stats:     3 lines in 1 file changed: 0 ins; 3 del; 0 mod

8272968: AArch64: Remove redundant matching rules for commutative ops

Reviewed-by: ngasson

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

PR: https://git.openjdk.java.net/jdk/pull/5646