[PATCH] Teach genmatch.c to generate single-use restrictions from flags
Bernhard Reutner-Fischer
rep.dot.nop@gmail.com
Mon Sep 14 15:41:00 GMT 2015
On September 14, 2015 11:23:28 AM GMT+02:00, Richard Biener <rguenther@suse.de> wrote:
>On Fri, 11 Sep 2015, Bernd Schmidt wrote:
>
>> On 07/08/2015 04:39 PM, Richard Biener wrote:
>> >
>> > This introduces a :s flag to match expressions which enforces
>> > the expression to have a single-use if(!) the simplified
>> > expression is larger than one statement.
>>
>> This seems to be missing documentation in match-and-simplify.texi.
>
>Fixed as follows, built and inspected .info and .pdf on x86_64-linux,
>applied.
>
>Richard.
>
>2015-09-14 Richard Biener <rguenther@suse.de>
>
> * doc/match-and-simplify.texi: Fixup some formatting issues
> and document the 's' flag.
>
>Index: gcc/doc/match-and-simplify.texi
>===================================================================
>--- gcc/doc/match-and-simplify.texi (revision 227737)
>+++ gcc/doc/match-and-simplify.texi (working copy)
>@@ -186,20 +186,36 @@ preprocessor directives.
> (bit_and @@1 @@0))
> @end smallexample
>
>-Here we introduce flags on match expressions. There is currently
>-a single flag, @code{c}, which denotes that the expression should
>+Here we introduce flags on match expressions. There used flag
s/There used flag/The flag used/
Thanks,
>+above, @code{c}, denotes that the expression should
> be also matched commutated. Thus the above match expression
> is really the following four match expressions:
>
>+@smallexample
> (bit_and integral_op_p@@0 (bit_ior (bit_not @@0) @@1))
> (bit_and (bit_ior (bit_not @@0) @@1) integral_op_p@@0)
> (bit_and integral_op_p@@0 (bit_ior @@1 (bit_not @@0)))
> (bit_and (bit_ior @@1 (bit_not @@0)) integral_op_p@@0)
>+@end smallexample
>
> Usual canonicalizations you know from GENERIC expressions are
> applied before matching, so for example constant operands always
> come second in commutative expressions.
>
>+The second supported flag is @code{s} which tells the code
>+generator to fail the pattern if the expression marked with
>+@code{s} does have more than one use. For example in
>+
>+@smallexample
>+(simplify
>+ (pointer_plus (pointer_plus:s @@0 @@1) @@3)
>+ (pointer_plus @@0 (plus @@1 @@3)))
>+@end smallexample
>+
>+this avoids the association if @code{(pointer_plus @@0 @@1)} is
>+used outside of the matched expression and thus it would stay
>+live and not trivially removed by dead code elimination.
>+
> More features exist to avoid too much repetition.
>
> @smallexample
>@@ -291,17 +307,17 @@ with a @code{?}:
>
> @smallexample
> (simplify
>- (eq (convert@@0 @@1) (convert? @@2))
>+ (eq (convert@@0 @@1) (convert@? @@2))
> (eq @@1 (convert @@2)))
> @end smallexample
>
> which will match both @code{(eq (convert @@1) (convert @@2))} and
> @code{(eq (convert @@1) @@2)}. The optional converts are supposed
> to be all either present or not, thus
>-@code{(eq (convert? @@1) (convert? @@2))} will result in two
>+@code{(eq (convert@? @@1) (convert@? @@2))} will result in two
> patterns only. If you want to match all four combinations you
> have access to two additional conditional converts as in
>-@code{(eq (convert1? @@1) (convert2? @@2))}.
>+@code{(eq (convert1@? @@1) (convert2@? @@2))}.
>
> Predicates available from the GCC middle-end need to be made
> available explicitely via @code{define_predicates}:
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