| Message ID | 5eef1b19afac0f6608f5a44e9560ca703752d689.1721743570.git.sam@gentoo.org |
|---|---|
| State | New |
| Headers | show |
| Series | doc: Document -O1 as the preferred level for large machine-generated code | expand |
Sam James <sam@gentoo.org> writes: (oops, forgot to CC docs maintainers. Done now.) > At -O1, the intention is that we compile things in a "reasonable" amount > of time (ditto memory use). In particular, we try to especially avoid > optimizations which scale poorly on pathological cases, as is the case > for large machine-generated code. > > Recommend -O1 for large machine-generated code, as has been informally > done on bugs for a while now. > > This applies (broadly speaking) for both large machine-generated functions > but also to a lesser extent repetitive small-but-still-not-tiny functions > from a generator program. > > gcc/ChangeLog: > PR middle-end/114855 > * doc/invoke.texi (Optimize options): Mention machine-generated > code for -O1. > --- > richi, does this accurately reflect the discussion we had on IRC a little > while ago? > > Please push if OK, thanks. > > gcc/doc/invoke.texi | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi > index e0a641213ae4..9fb0925ed292 100644 > --- a/gcc/doc/invoke.texi > +++ b/gcc/doc/invoke.texi > @@ -12560,6 +12560,11 @@ With @option{-O}, the compiler tries to reduce code size and execution > time, without performing any optimizations that take a great deal of > compilation time. > > +@option{-O} is the recommended optimization level for large machine-generated > +code as a sensible balance between time taken to compile and memory use: > +higher optimization levels perform optimizations with greater algorithmic > +complexity than at @option{-O}. > + > @c Note that in addition to the default_options_table list in opts.cc, > @c several optimization flags default to true but control optimization > @c passes that are explicitly disabled at -O0.
On Tue, Jul 23, 2024 at 10:07 AM Sam James <sam@gentoo.org> wrote: > > At -O1, the intention is that we compile things in a "reasonable" amount > of time (ditto memory use). In particular, we try to especially avoid > optimizations which scale poorly on pathological cases, as is the case > for large machine-generated code. > > Recommend -O1 for large machine-generated code, as has been informally > done on bugs for a while now. > > This applies (broadly speaking) for both large machine-generated functions > but also to a lesser extent repetitive small-but-still-not-tiny functions > from a generator program. > > gcc/ChangeLog: > PR middle-end/114855 > * doc/invoke.texi (Optimize options): Mention machine-generated > code for -O1. > --- > richi, does this accurately reflect the discussion we had on IRC a little > while ago? > > Please push if OK, thanks. > > gcc/doc/invoke.texi | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi > index e0a641213ae4..9fb0925ed292 100644 > --- a/gcc/doc/invoke.texi > +++ b/gcc/doc/invoke.texi > @@ -12560,6 +12560,11 @@ With @option{-O}, the compiler tries to reduce code size and execution > time, without performing any optimizations that take a great deal of > compilation time. > > +@option{-O} is the recommended optimization level for large machine-generated > +code as a sensible balance between time taken to compile and memory use: > +higher optimization levels perform optimizations with greater algorithmic > +complexity than at @option{-O}. > + Personally, I get confused when "-O1" is written as just "-O"... > @c Note that in addition to the default_options_table list in opts.cc, > @c several optimization flags default to true but control optimization > @c passes that are explicitly disabled at -O0. > > -- > 2.45.2 >
Eric Gallager <egall@gwmail.gwu.edu> writes: > On Tue, Jul 23, 2024 at 10:07 AM Sam James <sam@gentoo.org> wrote: >> >> At -O1, the intention is that we compile things in a "reasonable" amount >> of time (ditto memory use). In particular, we try to especially avoid >> optimizations which scale poorly on pathological cases, as is the case >> for large machine-generated code. >> >> Recommend -O1 for large machine-generated code, as has been informally >> done on bugs for a while now. >> >> This applies (broadly speaking) for both large machine-generated functions >> but also to a lesser extent repetitive small-but-still-not-tiny functions >> from a generator program. >> >> gcc/ChangeLog: >> PR middle-end/114855 >> * doc/invoke.texi (Optimize options): Mention machine-generated >> code for -O1. >> --- >> richi, does this accurately reflect the discussion we had on IRC a little >> while ago? >> >> Please push if OK, thanks. >> >> gcc/doc/invoke.texi | 5 +++++ >> 1 file changed, 5 insertions(+) >> >> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi >> index e0a641213ae4..9fb0925ed292 100644 >> --- a/gcc/doc/invoke.texi >> +++ b/gcc/doc/invoke.texi >> @@ -12560,6 +12560,11 @@ With @option{-O}, the compiler tries to reduce code size and execution >> time, without performing any optimizations that take a great deal of >> compilation time. >> >> +@option{-O} is the recommended optimization level for large machine-generated >> +code as a sensible balance between time taken to compile and memory use: >> +higher optimization levels perform optimizations with greater algorithmic >> +complexity than at @option{-O}. >> + > > Personally, I get confused when "-O1" is written as just "-O"... I, too, prefer -O1, but I was trying to be good and stick to convention. But then I did -O1 in the commit message. If people are fine with it, I'd prefer to do -O1. thanks, sam
On Tue, Jul 23, 2024 at 4:07 PM Sam James <sam@gentoo.org> wrote: > > At -O1, the intention is that we compile things in a "reasonable" amount > of time (ditto memory use). In particular, we try to especially avoid > optimizations which scale poorly on pathological cases, as is the case > for large machine-generated code. > > Recommend -O1 for large machine-generated code, as has been informally > done on bugs for a while now. > > This applies (broadly speaking) for both large machine-generated functions > but also to a lesser extent repetitive small-but-still-not-tiny functions > from a generator program. > > gcc/ChangeLog: > PR middle-end/114855 > * doc/invoke.texi (Optimize options): Mention machine-generated > code for -O1. > --- > richi, does this accurately reflect the discussion we had on IRC a little > while ago? > > Please push if OK, thanks. OK (I pushed it). Richard. > gcc/doc/invoke.texi | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi > index e0a641213ae4..9fb0925ed292 100644 > --- a/gcc/doc/invoke.texi > +++ b/gcc/doc/invoke.texi > @@ -12560,6 +12560,11 @@ With @option{-O}, the compiler tries to reduce code size and execution > time, without performing any optimizations that take a great deal of > compilation time. > > +@option{-O} is the recommended optimization level for large machine-generated > +code as a sensible balance between time taken to compile and memory use: > +higher optimization levels perform optimizations with greater algorithmic > +complexity than at @option{-O}. > + > @c Note that in addition to the default_options_table list in opts.cc, > @c several optimization flags default to true but control optimization > @c passes that are explicitly disabled at -O0. > > -- > 2.45.2 >
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi index e0a641213ae4..9fb0925ed292 100644 --- a/gcc/doc/invoke.texi +++ b/gcc/doc/invoke.texi @@ -12560,6 +12560,11 @@ With @option{-O}, the compiler tries to reduce code size and execution time, without performing any optimizations that take a great deal of compilation time. +@option{-O} is the recommended optimization level for large machine-generated +code as a sensible balance between time taken to compile and memory use: +higher optimization levels perform optimizations with greater algorithmic +complexity than at @option{-O}. + @c Note that in addition to the default_options_table list in opts.cc, @c several optimization flags default to true but control optimization @c passes that are explicitly disabled at -O0.