On Thu, Sep 14, 2023 at 10:54 AM Joseph Myers <jos...@codesourcery.com> wrote:
>
> On Wed, 13 Sep 2023, Ken Matsui via Gcc-patches wrote:
>
> > diff --git a/gcc/c/c-parser.h b/gcc/c/c-parser.h
> > index 545f0f4d9eb..eed6deaf0f8 100644
> > --- a/gcc/c/c-parser.h
> > +++ b/gcc/c/c-parser.h
> > @@ -51,14 +51,14 @@ enum c_id_kind {
> > /* A single C token after string literal concatenation and conversion
> > of preprocessing tokens to tokens. */
> > struct GTY (()) c_token {
> > + /* If this token is a keyword, this value indicates which keyword.
> > + Otherwise, this value is RID_MAX. */
> > + ENUM_BITFIELD (rid) keyword : 16;
> > /* The kind of token. */
> > ENUM_BITFIELD (cpp_ttype) type : 8;
> > /* If this token is a CPP_NAME, this value indicates whether also
> > declared as some kind of type. Otherwise, it is C_ID_NONE. */
> > ENUM_BITFIELD (c_id_kind) id_kind : 8;
> > - /* If this token is a keyword, this value indicates which keyword.
> > - Otherwise, this value is RID_MAX. */
> > - ENUM_BITFIELD (rid) keyword : 8;
> > /* If this token is a CPP_PRAGMA, this indicates the pragma that
> > was seen. Otherwise it is PRAGMA_NONE. */
> > ENUM_BITFIELD (pragma_kind) pragma_kind : 8;
>
> If you want to optimize layout, I'd expect flags to move so it can share
> the same 32-bit unit as the pragma_kind bit-field (not sure if any changes
> should be made to the declaration of flags to maximise the chance of such
> sharing across different host bit-field ABIs).
>
> > diff --git a/gcc/cp/parser.h b/gcc/cp/parser.h
> > index 6cbb9a8e031..3c3c482c6ce 100644
> > --- a/gcc/cp/parser.h
> > +++ b/gcc/cp/parser.h
> > @@ -40,11 +40,11 @@ struct GTY(()) tree_check {
> > /* A C++ token. */
> >
> > struct GTY (()) cp_token {
> > - /* The kind of token. */
> > - enum cpp_ttype type : 8;
> > /* If this token is a keyword, this value indicates which keyword.
> > Otherwise, this value is RID_MAX. */
> > - enum rid keyword : 8;
> > + enum rid keyword : 16;
> > + /* The kind of token. */
> > + enum cpp_ttype type : 8;
> > /* Token flags. */
> > unsigned char flags;
> > /* True if this token is from a context where it is implicitly extern
> > "C" */
>
> You're missing an update to the "3 unused bits." comment further down.
>
> > @@ -988,7 +988,7 @@ struct GTY(()) cpp_hashnode {
> > unsigned int directive_index : 7; /* If is_directive,
> > then index into directive table.
> > Otherwise, a NODE_OPERATOR. */
> > - unsigned int rid_code : 8; /* Rid code - for front ends. */
> > + unsigned int rid_code : 16; /* Rid code - for front ends.
> > */
> > unsigned int flags : 9; /* CPP flags. */
> > ENUM_BITFIELD(node_type) type : 2; /* CPP node type. */
>
> You're missing an update to the "5 bits spare." comment further down.
>
> Do you have any figures for the effects on compilation time or memory
> usage from the increase in size of these structures?
>
Here is the benchmark result:
https://github.com/ken-matsui/gsoc23/tree/main/reports/gcc-build
I can see regression for compilation time but not for memory.
* Time: +0.950995%
* Memory: No difference proven at 95.0% confidence
Sincerely,
Ken Matsui
> --
> Joseph S. Myers
> jos...@codesourcery.com
