| Message ID | 20210903135832.735852-1-aldyh@redhat.com |
|---|---|
| State | New |
| Headers | show |
| Series | Abstract PHI and forwarder block checks in jump threader. | expand |
On Fri, Sep 3, 2021 at 3:59 PM Aldy Hernandez via Gcc-patches <gcc-patches@gcc.gnu.org> wrote: > > This patch abstracts out a couple common idioms in the forward > threader that I found useful while navigating the code base. > > Tested on x86-64 Linux. > > OK? > > gcc/ChangeLog: > > * tree-ssa-threadedge.c (has_phis_p): New. > (forwarder_block_p): New. > (potentially_threadable_block): Call forwarder_block_p. > (jump_threader::thread_around_empty_blocks): Call has_phis_p. > (jump_threader::thread_through_normal_block): Call > forwarder_block_p. > --- > gcc/tree-ssa-threadedge.c | 25 +++++++++++++++++++------ > 1 file changed, 19 insertions(+), 6 deletions(-) > > diff --git a/gcc/tree-ssa-threadedge.c b/gcc/tree-ssa-threadedge.c > index e57f6d3e39c..3db54a199fd 100644 > --- a/gcc/tree-ssa-threadedge.c > +++ b/gcc/tree-ssa-threadedge.c > @@ -95,6 +95,21 @@ jump_threader::thread_through_all_blocks (bool may_peel_loop_headers) > return m_registry->thread_through_all_blocks (may_peel_loop_headers); > } > > +static inline bool > +has_phis_p (basic_block bb) > +{ > + return !gsi_end_p (gsi_start_phis (bb)); gimple_seq_empty_p (phi_nodes (bb)) shoud be cheaper. Do virtual PHIs count as PHIs for you? > +} > + > +/* Return TRUE for a forwarder block which is defined as having PHIs > + but no instructions. */ > + > +static bool > +forwarder_block_p (basic_block bb) There exists a function with exactly the same signature in cfgrtl.h, likewise several similar implementations might exist elsewhere. Your definition is also quite odd, not matching what one would expect (the PHI requirement). The tree-cfgcleanup.c variant has tree_forwarder_block_p which is explicit about this. Btw, gsi_start_nondebug_bb does not ignore labels. > +{ > + return gsi_end_p (gsi_start_nondebug_bb (bb)) && has_phis_p (bb); > +} > + > /* Return TRUE if we may be able to thread an incoming edge into > BB to an outgoing edge from BB. Return FALSE otherwise. */ > > @@ -107,9 +122,8 @@ potentially_threadable_block (basic_block bb) > not optimized away because they forward from outside a loop > to the loop header. We want to thread through them as we can > sometimes thread to the loop exit, which is obviously profitable. > - the interesting case here is when the block has PHIs. */ > - if (gsi_end_p (gsi_start_nondebug_bb (bb)) > - && !gsi_end_p (gsi_start_phis (bb))) > + The interesting case here is when the block has PHIs. */ > + if (forwarder_block_p (bb)) > return true; > > /* If BB has a single successor or a single predecessor, then > @@ -854,7 +868,7 @@ jump_threader::thread_around_empty_blocks (vec<jump_thread_edge *> *path, > /* The key property of these blocks is that they need not be duplicated > when threading. Thus they cannot have visible side effects such > as PHI nodes. */ > - if (!gsi_end_p (gsi_start_phis (bb))) > + if (has_phis_p (bb)) > return false; > > /* Skip over DEBUG statements at the start of the block. */ > @@ -994,8 +1008,7 @@ jump_threader::thread_through_normal_block (vec<jump_thread_edge *> *path, > { > /* First case. The statement simply doesn't have any instructions, but > does have PHIs. */ > - if (gsi_end_p (gsi_start_nondebug_bb (e->dest)) > - && !gsi_end_p (gsi_start_phis (e->dest))) > + if (forwarder_block_p (e->dest)) > return 0; > > /* Second case. */ > -- > 2.31.1 >
On 9/6/21 9:19 AM, Richard Biener wrote: > On Fri, Sep 3, 2021 at 3:59 PM Aldy Hernandez via Gcc-patches > <gcc-patches@gcc.gnu.org> wrote: >> >> This patch abstracts out a couple common idioms in the forward >> threader that I found useful while navigating the code base. >> >> Tested on x86-64 Linux. >> >> OK? >> >> gcc/ChangeLog: >> >> * tree-ssa-threadedge.c (has_phis_p): New. >> (forwarder_block_p): New. >> (potentially_threadable_block): Call forwarder_block_p. >> (jump_threader::thread_around_empty_blocks): Call has_phis_p. >> (jump_threader::thread_through_normal_block): Call >> forwarder_block_p. >> --- >> gcc/tree-ssa-threadedge.c | 25 +++++++++++++++++++------ >> 1 file changed, 19 insertions(+), 6 deletions(-) >> >> diff --git a/gcc/tree-ssa-threadedge.c b/gcc/tree-ssa-threadedge.c >> index e57f6d3e39c..3db54a199fd 100644 >> --- a/gcc/tree-ssa-threadedge.c >> +++ b/gcc/tree-ssa-threadedge.c >> @@ -95,6 +95,21 @@ jump_threader::thread_through_all_blocks (bool may_peel_loop_headers) >> return m_registry->thread_through_all_blocks (may_peel_loop_headers); >> } >> >> +static inline bool >> +has_phis_p (basic_block bb) >> +{ >> + return !gsi_end_p (gsi_start_phis (bb)); > > gimple_seq_empty_p (phi_nodes (bb)) shoud be cheaper. Do virtual PHIs > count as PHIs for you? I don't know. The goal was to abstract some common idioms without changing existing behavior, but if my abstractions confuse other readers, perhaps I should revert my patch. FWIW, my initial motivation here was to merge the path profitability code between the forward and backward threaders. It seems the forward threader is more permissive than the backward threader, even though the latter can thread more paths than it's allowed (per profitable_path_p). > >> +} >> + >> +/* Return TRUE for a forwarder block which is defined as having PHIs >> + but no instructions. */ >> + >> +static bool >> +forwarder_block_p (basic_block bb) > > There exists a function with exactly the same signature in cfgrtl.h, likewise > several similar implementations might exist elsewhere. Ughh, that's definitely not good. > > Your definition is also quite odd, not matching what one would expect > (the PHI requirement). The tree-cfgcleanup.c variant has > tree_forwarder_block_p which is explicit about this. > > Btw, gsi_start_nondebug_bb does not ignore labels. Would a name like empty_block_with_phis_p be more appropriate? Aldy
On September 7, 2021 12:02:27 PM GMT+02:00, Aldy Hernandez <aldyh@redhat.com> wrote: > > >On 9/6/21 9:19 AM, Richard Biener wrote: >> On Fri, Sep 3, 2021 at 3:59 PM Aldy Hernandez via Gcc-patches >> <gcc-patches@gcc.gnu.org> wrote: >>> >>> This patch abstracts out a couple common idioms in the forward >>> threader that I found useful while navigating the code base. >>> >>> Tested on x86-64 Linux. >>> >>> OK? >>> >>> gcc/ChangeLog: >>> >>> * tree-ssa-threadedge.c (has_phis_p): New. >>> (forwarder_block_p): New. >>> (potentially_threadable_block): Call forwarder_block_p. >>> (jump_threader::thread_around_empty_blocks): Call has_phis_p. >>> (jump_threader::thread_through_normal_block): Call >>> forwarder_block_p. >>> --- >>> gcc/tree-ssa-threadedge.c | 25 +++++++++++++++++++------ >>> 1 file changed, 19 insertions(+), 6 deletions(-) >>> >>> diff --git a/gcc/tree-ssa-threadedge.c b/gcc/tree-ssa-threadedge.c >>> index e57f6d3e39c..3db54a199fd 100644 >>> --- a/gcc/tree-ssa-threadedge.c >>> +++ b/gcc/tree-ssa-threadedge.c >>> @@ -95,6 +95,21 @@ jump_threader::thread_through_all_blocks (bool may_peel_loop_headers) >>> return m_registry->thread_through_all_blocks (may_peel_loop_headers); >>> } >>> >>> +static inline bool >>> +has_phis_p (basic_block bb) >>> +{ >>> + return !gsi_end_p (gsi_start_phis (bb)); >> >> gimple_seq_empty_p (phi_nodes (bb)) shoud be cheaper. Do virtual PHIs >> count as PHIs for you? > >I don't know. The goal was to abstract some common idioms without >changing existing behavior, but if my abstractions confuse other >readers, perhaps I should revert my patch. > >FWIW, my initial motivation here was to merge the path profitability >code between the forward and backward threaders. It seems the forward >threader is more permissive than the backward threader, even though the >latter can thread more paths than it's allowed (per profitable_path_p). > >> >>> +} >>> + >>> +/* Return TRUE for a forwarder block which is defined as having PHIs >>> + but no instructions. */ >>> + >>> +static bool >>> +forwarder_block_p (basic_block bb) >> >> There exists a function with exactly the same signature in cfgrtl.h, likewise >> several similar implementations might exist elsewhere. > >Ughh, that's definitely not good. > >> >> Your definition is also quite odd, not matching what one would expect >> (the PHI requirement). The tree-cfgcleanup.c variant has >> tree_forwarder_block_p which is explicit about this. >> >> Btw, gsi_start_nondebug_bb does not ignore labels. > >Would a name like empty_block_with_phis_p be more appropriate? I think so. That said, my main concern ist the clash with the same named function. Richard. >Aldy >
On 9/7/21 2:59 PM, Richard Biener wrote: > On September 7, 2021 12:02:27 PM GMT+02:00, Aldy Hernandez <aldyh@redhat.com> wrote: >> >> >> On 9/6/21 9:19 AM, Richard Biener wrote: >>> On Fri, Sep 3, 2021 at 3:59 PM Aldy Hernandez via Gcc-patches >>> <gcc-patches@gcc.gnu.org> wrote: >>>> >>>> This patch abstracts out a couple common idioms in the forward >>>> threader that I found useful while navigating the code base. >>>> >>>> Tested on x86-64 Linux. >>>> >>>> OK? >>>> >>>> gcc/ChangeLog: >>>> >>>> * tree-ssa-threadedge.c (has_phis_p): New. >>>> (forwarder_block_p): New. >>>> (potentially_threadable_block): Call forwarder_block_p. >>>> (jump_threader::thread_around_empty_blocks): Call has_phis_p. >>>> (jump_threader::thread_through_normal_block): Call >>>> forwarder_block_p. >>>> --- >>>> gcc/tree-ssa-threadedge.c | 25 +++++++++++++++++++------ >>>> 1 file changed, 19 insertions(+), 6 deletions(-) >>>> >>>> diff --git a/gcc/tree-ssa-threadedge.c b/gcc/tree-ssa-threadedge.c >>>> index e57f6d3e39c..3db54a199fd 100644 >>>> --- a/gcc/tree-ssa-threadedge.c >>>> +++ b/gcc/tree-ssa-threadedge.c >>>> @@ -95,6 +95,21 @@ jump_threader::thread_through_all_blocks (bool may_peel_loop_headers) >>>> return m_registry->thread_through_all_blocks (may_peel_loop_headers); >>>> } >>>> >>>> +static inline bool >>>> +has_phis_p (basic_block bb) >>>> +{ >>>> + return !gsi_end_p (gsi_start_phis (bb)); >>> >>> gimple_seq_empty_p (phi_nodes (bb)) shoud be cheaper. Do virtual PHIs >>> count as PHIs for you? >> >> I don't know. The goal was to abstract some common idioms without >> changing existing behavior, but if my abstractions confuse other >> readers, perhaps I should revert my patch. >> >> FWIW, my initial motivation here was to merge the path profitability >> code between the forward and backward threaders. It seems the forward >> threader is more permissive than the backward threader, even though the >> latter can thread more paths than it's allowed (per profitable_path_p). >> >>> >>>> +} >>>> + >>>> +/* Return TRUE for a forwarder block which is defined as having PHIs >>>> + but no instructions. */ >>>> + >>>> +static bool >>>> +forwarder_block_p (basic_block bb) >>> >>> There exists a function with exactly the same signature in cfgrtl.h, likewise >>> several similar implementations might exist elsewhere. >> >> Ughh, that's definitely not good. >> >>> >>> Your definition is also quite odd, not matching what one would expect >>> (the PHI requirement). The tree-cfgcleanup.c variant has >>> tree_forwarder_block_p which is explicit about this. >>> >>> Btw, gsi_start_nondebug_bb does not ignore labels. >> >> Would a name like empty_block_with_phis_p be more appropriate? > > I think so. That said, my main concern ist the clash with the same named function. Agreed. OK for trunk? Aldy
On 9/7/2021 7:23 AM, Aldy Hernandez wrote: > > > On 9/7/21 2:59 PM, Richard Biener wrote: >> On September 7, 2021 12:02:27 PM GMT+02:00, Aldy Hernandez >> <aldyh@redhat.com> wrote: >>> >>> >>> On 9/6/21 9:19 AM, Richard Biener wrote: >>>> On Fri, Sep 3, 2021 at 3:59 PM Aldy Hernandez via Gcc-patches >>>> <gcc-patches@gcc.gnu.org> wrote: >>>>> >>>>> This patch abstracts out a couple common idioms in the forward >>>>> threader that I found useful while navigating the code base. >>>>> >>>>> Tested on x86-64 Linux. >>>>> >>>>> OK? >>>>> >>>>> gcc/ChangeLog: >>>>> >>>>> * tree-ssa-threadedge.c (has_phis_p): New. >>>>> (forwarder_block_p): New. >>>>> (potentially_threadable_block): Call forwarder_block_p. >>>>> (jump_threader::thread_around_empty_blocks): Call >>>>> has_phis_p. >>>>> (jump_threader::thread_through_normal_block): Call >>>>> forwarder_block_p. >>>>> --- >>>>> gcc/tree-ssa-threadedge.c | 25 +++++++++++++++++++------ >>>>> 1 file changed, 19 insertions(+), 6 deletions(-) >>>>> >>>>> diff --git a/gcc/tree-ssa-threadedge.c b/gcc/tree-ssa-threadedge.c >>>>> index e57f6d3e39c..3db54a199fd 100644 >>>>> --- a/gcc/tree-ssa-threadedge.c >>>>> +++ b/gcc/tree-ssa-threadedge.c >>>>> @@ -95,6 +95,21 @@ jump_threader::thread_through_all_blocks (bool >>>>> may_peel_loop_headers) >>>>> return m_registry->thread_through_all_blocks >>>>> (may_peel_loop_headers); >>>>> } >>>>> >>>>> +static inline bool >>>>> +has_phis_p (basic_block bb) >>>>> +{ >>>>> + return !gsi_end_p (gsi_start_phis (bb)); >>>> >>>> gimple_seq_empty_p (phi_nodes (bb)) shoud be cheaper. Do virtual PHIs >>>> count as PHIs for you? >>> >>> I don't know. The goal was to abstract some common idioms without >>> changing existing behavior, but if my abstractions confuse other >>> readers, perhaps I should revert my patch. >>> >>> FWIW, my initial motivation here was to merge the path profitability >>> code between the forward and backward threaders. It seems the forward >>> threader is more permissive than the backward threader, even though the >>> latter can thread more paths than it's allowed (per profitable_path_p). >>> >>>> >>>>> +} >>>>> + >>>>> +/* Return TRUE for a forwarder block which is defined as having PHIs >>>>> + but no instructions. */ >>>>> + >>>>> +static bool >>>>> +forwarder_block_p (basic_block bb) >>>> >>>> There exists a function with exactly the same signature in >>>> cfgrtl.h, likewise >>>> several similar implementations might exist elsewhere. >>> >>> Ughh, that's definitely not good. >>> >>>> >>>> Your definition is also quite odd, not matching what one would expect >>>> (the PHI requirement). The tree-cfgcleanup.c variant has >>>> tree_forwarder_block_p which is explicit about this. >>>> >>>> Btw, gsi_start_nondebug_bb does not ignore labels. >>> >>> Would a name like empty_block_with_phis_p be more appropriate? >> >> I think so. That said, my main concern ist the clash with the same >> named function. > > Agreed. > > OK for trunk? > > Aldy > > > p.patch > > commit 77ac56456d5db150d6a71eaca918f19d2b478f82 > Author: Aldy Hernandez <aldyh@redhat.com> > Date: Tue Sep 7 15:20:23 2021 +0200 > > Rename forwarder_block_p in treading code to empty_block_with_phis_p. > > gcc/ChangeLog: > > * tree-ssa-threadedge.c (forwarder_block_p): Rename to... > (empty_block_with_phis_p): ...this. > (potentially_threadable_block): Same. > (jump_threader::thread_through_normal_block): Same. OK. I nearly called out a request for a name change.... Guess I should have :-) jeff
diff --git a/gcc/tree-ssa-threadedge.c b/gcc/tree-ssa-threadedge.c index e57f6d3e39c..3db54a199fd 100644 --- a/gcc/tree-ssa-threadedge.c +++ b/gcc/tree-ssa-threadedge.c @@ -95,6 +95,21 @@ jump_threader::thread_through_all_blocks (bool may_peel_loop_headers) return m_registry->thread_through_all_blocks (may_peel_loop_headers); } +static inline bool +has_phis_p (basic_block bb) +{ + return !gsi_end_p (gsi_start_phis (bb)); +} + +/* Return TRUE for a forwarder block which is defined as having PHIs + but no instructions. */ + +static bool +forwarder_block_p (basic_block bb) +{ + return gsi_end_p (gsi_start_nondebug_bb (bb)) && has_phis_p (bb); +} + /* Return TRUE if we may be able to thread an incoming edge into BB to an outgoing edge from BB. Return FALSE otherwise. */ @@ -107,9 +122,8 @@ potentially_threadable_block (basic_block bb) not optimized away because they forward from outside a loop to the loop header. We want to thread through them as we can sometimes thread to the loop exit, which is obviously profitable. - the interesting case here is when the block has PHIs. */ - if (gsi_end_p (gsi_start_nondebug_bb (bb)) - && !gsi_end_p (gsi_start_phis (bb))) + The interesting case here is when the block has PHIs. */ + if (forwarder_block_p (bb)) return true; /* If BB has a single successor or a single predecessor, then @@ -854,7 +868,7 @@ jump_threader::thread_around_empty_blocks (vec<jump_thread_edge *> *path, /* The key property of these blocks is that they need not be duplicated when threading. Thus they cannot have visible side effects such as PHI nodes. */ - if (!gsi_end_p (gsi_start_phis (bb))) + if (has_phis_p (bb)) return false; /* Skip over DEBUG statements at the start of the block. */ @@ -994,8 +1008,7 @@ jump_threader::thread_through_normal_block (vec<jump_thread_edge *> *path, { /* First case. The statement simply doesn't have any instructions, but does have PHIs. */ - if (gsi_end_p (gsi_start_nondebug_bb (e->dest)) - && !gsi_end_p (gsi_start_phis (e->dest))) + if (forwarder_block_p (e->dest)) return 0; /* Second case. */