| Message ID | 20241105032000.381511-1-MayShao-oc@zhaoxin.com |
|---|---|
| State | New |
| Headers | show |
| Series | [x86_64] Add flag to control tight loops alignment opt | expand |
> -----Original Message----- > From: MayShao-oc <MayShao-oc@zhaoxin.com> > Sent: Tuesday, November 5, 2024 11:20 AM > To: gcc-patches@gcc.gnu.org; hubicka@ucw.cz; Liu, Hongtao > <hongtao.liu@intel.com>; ubizjak@gmail.com > Cc: timhu@zhaoxin.com; silviazhao@zhaoxin.com; louisqi@zhaoxin.com; > cobechen@zhaoxin.com > Subject: [PATCH] [x86_64] Add flag to control tight loops alignment opt > > Hi all: > This patch add -malign-tight-loops flag to control pass_align_tight_loops. > The motivation is that pass_align_tight_loops may cause performance > regression in nested loops. > > The example code as follows: > > #define ITER 20000 > #define ITER_O 10 > > int i, j,k; > int array[ITER]; > > void loop() > { > int i; > for(k = 0; k < ITER_O; k++) > for(j = 0; j < ITER; j++) > for(i = 0; i < ITER; i++) > { > array[i] += j; > array[i] += i; > array[i] += 2*j; > array[i] += 2*i; > } > } > > When I compile it with gcc -O1 loop.c, the output assembly as follows. > It is not optimal, because of too many nops insert in the outer loop. > > 0000000000400540 <loop>: > 400540: 48 83 ec 08 sub $0x8,%rsp > 400544: bf 0a 00 00 00 mov $0xa,%edi > 400549: b9 00 00 00 00 mov $0x0,%ecx > 40054e: 8d 34 09 lea (%rcx,%rcx,1),%esi > 400551: b8 00 00 00 00 mov $0x0,%eax > 400556: 66 66 2e 0f 1f 84 00 data16 nopw %cs:0x0(%rax,%rax,1) > 40055d: 00 00 00 00 > 400561: 66 66 2e 0f 1f 84 00 data16 nopw %cs:0x0(%rax,%rax,1) > 400568: 00 00 00 00 > 40056c: 66 66 2e 0f 1f 84 00 data16 nopw %cs:0x0(%rax,%rax,1) > 400573: 00 00 00 00 > 400577: 66 0f 1f 84 00 00 00 nopw 0x0(%rax,%rax,1) > 40057e: 00 00 > 400580: 89 ca mov %ecx,%edx > 400582: 03 14 85 60 10 60 00 add 0x601060(,%rax,4),%edx > 400589: 01 c2 add %eax,%edx > 40058b: 01 f2 add %esi,%edx > 40058d: 8d 14 42 lea (%rdx,%rax,2),%edx > 400590: 89 14 85 60 10 60 00 mov %edx,0x601060(,%rax,4) > 400597: 48 83 c0 01 add $0x1,%rax > 40059b: 48 3d 20 4e 00 00 cmp $0x4e20,%rax > 4005a1: 75 dd jne 400580 <loop+0x40> > > I benchmark this program in the intel Xeon, and find the optimization may > cause a 40% performance regression (6.6B cycles VS 9.3B cycles). > So I propose to add -malign-tight-loops flag to control tight loop > optimization to avoid this, we could disalbe this optimization by default. > Bootstrapped X86_64. > Ok for trunk? > > BR > Mayshao > > gcc/ChangeLog: > > * config/i386/i386-features.cc (ix86_align_tight_loops): New flag. > * config/i386/i386.opt (malign-tight-loops): New option. > * doc/invoke.texi (-malign-tight-loops): Document. > --- > gcc/config/i386/i386-features.cc | 4 +++- > gcc/config/i386/i386.opt | 4 ++++ > gcc/doc/invoke.texi | 7 ++++++- > 3 files changed, 13 insertions(+), 2 deletions(-) > > diff --git a/gcc/config/i386/i386-features.cc b/gcc/config/i386/i386- > features.cc > index e2e85212a4f..f9546e00b07 100644 > --- a/gcc/config/i386/i386-features.cc > +++ b/gcc/config/i386/i386-features.cc > @@ -3620,7 +3620,9 @@ public: > /* opt_pass methods: */ > bool gate (function *) final override > { > - return optimize && optimize_function_for_speed_p (cfun); > + return ix86_align_tight_loops > + && optimize > + && optimize_function_for_speed_p (cfun); > } > > unsigned int execute (function *) final override diff --git > a/gcc/config/i386/i386.opt b/gcc/config/i386/i386.opt index > 64c295d344c..ec41de192bc 100644 > --- a/gcc/config/i386/i386.opt > +++ b/gcc/config/i386/i386.opt > @@ -1266,6 +1266,10 @@ mlam= > Target RejectNegative Joined Enum(lam_type) Var(ix86_lam_type) > Init(lam_none) -mlam=[none|u48|u57] Instrument meta data position in > user data pointers. > > +malign-tight-loops > +Target Var(ix86_align_tight_loops) Init(0) Optimization Enable align > +tight loops. I'd like it to be on by default, so Init (1)? > + > Enum > Name(lam_type) Type(enum lam_type) UnknownError(unknown lam > type %qs) > > diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi index > 07920e07b4d..9ec1e1f0095 100644 > --- a/gcc/doc/invoke.texi > +++ b/gcc/doc/invoke.texi > @@ -1510,7 +1510,7 @@ See RS/6000 and PowerPC Options. > -mindirect-branch=@var{choice} -mfunction-return=@var{choice} - > mindirect-branch-register -mharden-sls=@var{choice} -mindirect-branch-cs- > prefix -mneeded -mno-direct-extern-access --munroll-only-small-loops - > mlam=@var{choice}} > +-munroll-only-small-loops -mlam=@var{choice} -malign-tight-loops} > > @emph{x86 Windows Options} > > @@ -36530,6 +36530,11 @@ LAM(linear-address masking) allows special > bits in the pointer to be used for metadata. The default is @samp{none}. With > @samp{u48}, pointer bits in positions 62:48 can be used for metadata; With > @samp{u57}, pointer bits in positions 62:57 can be used for metadata. > + > +@opindex malign-tight-loops > +@opindex mno-align-tight-loops > +@item -malign-tight-loops > +Controls tight loop alignment optimization. > @end table > > @node x86 Windows Options > -- > 2.27.0
On Tue, Nov 5, 2024 at 2:34 PM Liu, Hongtao <hongtao.liu@intel.com> wrote: > > > > > -----Original Message----- > > From: MayShao-oc <MayShao-oc@zhaoxin.com> > > Sent: Tuesday, November 5, 2024 11:20 AM > > To: gcc-patches@gcc.gnu.org; hubicka@ucw.cz; Liu, Hongtao > > <hongtao.liu@intel.com>; ubizjak@gmail.com > > Cc: timhu@zhaoxin.com; silviazhao@zhaoxin.com; louisqi@zhaoxin.com; > > cobechen@zhaoxin.com > > Subject: [PATCH] [x86_64] Add flag to control tight loops alignment opt > > > > Hi all: > > This patch add -malign-tight-loops flag to control pass_align_tight_loops. > > The motivation is that pass_align_tight_loops may cause performance > > regression in nested loops. > > > > The example code as follows: > > > > #define ITER 20000 > > #define ITER_O 10 > > > > int i, j,k; > > int array[ITER]; > > > > void loop() > > { > > int i; > > for(k = 0; k < ITER_O; k++) > > for(j = 0; j < ITER; j++) > > for(i = 0; i < ITER; i++) > > { > > array[i] += j; > > array[i] += i; > > array[i] += 2*j; > > array[i] += 2*i; > > } > > } > > > > When I compile it with gcc -O1 loop.c, the output assembly as follows. > > It is not optimal, because of too many nops insert in the outer loop. > > > > 0000000000400540 <loop>: > > 400540: 48 83 ec 08 sub $0x8,%rsp > > 400544: bf 0a 00 00 00 mov $0xa,%edi > > 400549: b9 00 00 00 00 mov $0x0,%ecx > > 40054e: 8d 34 09 lea (%rcx,%rcx,1),%esi > > 400551: b8 00 00 00 00 mov $0x0,%eax > > 400556: 66 66 2e 0f 1f 84 00 data16 nopw %cs:0x0(%rax,%rax,1) > > 40055d: 00 00 00 00 > > 400561: 66 66 2e 0f 1f 84 00 data16 nopw %cs:0x0(%rax,%rax,1) > > 400568: 00 00 00 00 > > 40056c: 66 66 2e 0f 1f 84 00 data16 nopw %cs:0x0(%rax,%rax,1) > > 400573: 00 00 00 00 > > 400577: 66 0f 1f 84 00 00 00 nopw 0x0(%rax,%rax,1) > > 40057e: 00 00 > > 400580: 89 ca mov %ecx,%edx > > 400582: 03 14 85 60 10 60 00 add 0x601060(,%rax,4),%edx > > 400589: 01 c2 add %eax,%edx > > 40058b: 01 f2 add %esi,%edx > > 40058d: 8d 14 42 lea (%rdx,%rax,2),%edx > > 400590: 89 14 85 60 10 60 00 mov %edx,0x601060(,%rax,4) > > 400597: 48 83 c0 01 add $0x1,%rax > > 40059b: 48 3d 20 4e 00 00 cmp $0x4e20,%rax > > 4005a1: 75 dd jne 400580 <loop+0x40> > > > > I benchmark this program in the intel Xeon, and find the optimization may > > cause a 40% performance regression (6.6B cycles VS 9.3B cycles). On SPR, align is 25% better than no_align case. > > So I propose to add -malign-tight-loops flag to control tight loop > > optimization to avoid this, we could disalbe this optimization by default. > > Bootstrapped X86_64. > > Ok for trunk? > > > > BR > > Mayshao > > > > gcc/ChangeLog: > > > > * config/i386/i386-features.cc (ix86_align_tight_loops): New flag. > > * config/i386/i386.opt (malign-tight-loops): New option. > > * doc/invoke.texi (-malign-tight-loops): Document. > > --- > > gcc/config/i386/i386-features.cc | 4 +++- > > gcc/config/i386/i386.opt | 4 ++++ > > gcc/doc/invoke.texi | 7 ++++++- > > 3 files changed, 13 insertions(+), 2 deletions(-) > > > > diff --git a/gcc/config/i386/i386-features.cc b/gcc/config/i386/i386- > > features.cc > > index e2e85212a4f..f9546e00b07 100644 > > --- a/gcc/config/i386/i386-features.cc > > +++ b/gcc/config/i386/i386-features.cc > > @@ -3620,7 +3620,9 @@ public: > > /* opt_pass methods: */ > > bool gate (function *) final override > > { > > - return optimize && optimize_function_for_speed_p (cfun); > > + return ix86_align_tight_loops > > + && optimize > > + && optimize_function_for_speed_p (cfun); > > } > > > > unsigned int execute (function *) final override diff --git > > a/gcc/config/i386/i386.opt b/gcc/config/i386/i386.opt index > > 64c295d344c..ec41de192bc 100644 > > --- a/gcc/config/i386/i386.opt > > +++ b/gcc/config/i386/i386.opt > > @@ -1266,6 +1266,10 @@ mlam= > > Target RejectNegative Joined Enum(lam_type) Var(ix86_lam_type) > > Init(lam_none) -mlam=[none|u48|u57] Instrument meta data position in > > user data pointers. > > > > +malign-tight-loops > > +Target Var(ix86_align_tight_loops) Init(0) Optimization Enable align > > +tight loops. > > I'd like it to be on by default, so Init (1)? > > > + > > Enum > > Name(lam_type) Type(enum lam_type) UnknownError(unknown lam > > type %qs) > > > > diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi index > > 07920e07b4d..9ec1e1f0095 100644 > > --- a/gcc/doc/invoke.texi > > +++ b/gcc/doc/invoke.texi > > @@ -1510,7 +1510,7 @@ See RS/6000 and PowerPC Options. > > -mindirect-branch=@var{choice} -mfunction-return=@var{choice} - > > mindirect-branch-register -mharden-sls=@var{choice} -mindirect-branch-cs- > > prefix -mneeded -mno-direct-extern-access --munroll-only-small-loops - > > mlam=@var{choice}} > > +-munroll-only-small-loops -mlam=@var{choice} -malign-tight-loops} > > > > @emph{x86 Windows Options} > > > > @@ -36530,6 +36530,11 @@ LAM(linear-address masking) allows special > > bits in the pointer to be used for metadata. The default is @samp{none}. With > > @samp{u48}, pointer bits in positions 62:48 can be used for metadata; With > > @samp{u57}, pointer bits in positions 62:57 can be used for metadata. > > + > > +@opindex malign-tight-loops > > +@opindex mno-align-tight-loops > > +@item -malign-tight-loops > > +Controls tight loop alignment optimization. > > @end table > > > > @node x86 Windows Options > > -- > > 2.27.0 >
diff --git a/gcc/config/i386/i386-features.cc b/gcc/config/i386/i386-features.cc index e2e85212a4f..f9546e00b07 100644 --- a/gcc/config/i386/i386-features.cc +++ b/gcc/config/i386/i386-features.cc @@ -3620,7 +3620,9 @@ public: /* opt_pass methods: */ bool gate (function *) final override { - return optimize && optimize_function_for_speed_p (cfun); + return ix86_align_tight_loops + && optimize + && optimize_function_for_speed_p (cfun); } unsigned int execute (function *) final override diff --git a/gcc/config/i386/i386.opt b/gcc/config/i386/i386.opt index 64c295d344c..ec41de192bc 100644 --- a/gcc/config/i386/i386.opt +++ b/gcc/config/i386/i386.opt @@ -1266,6 +1266,10 @@ mlam= Target RejectNegative Joined Enum(lam_type) Var(ix86_lam_type) Init(lam_none) -mlam=[none|u48|u57] Instrument meta data position in user data pointers. +malign-tight-loops +Target Var(ix86_align_tight_loops) Init(0) Optimization +Enable align tight loops. + Enum Name(lam_type) Type(enum lam_type) UnknownError(unknown lam type %qs) diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi index 07920e07b4d..9ec1e1f0095 100644 --- a/gcc/doc/invoke.texi +++ b/gcc/doc/invoke.texi @@ -1510,7 +1510,7 @@ See RS/6000 and PowerPC Options. -mindirect-branch=@var{choice} -mfunction-return=@var{choice} -mindirect-branch-register -mharden-sls=@var{choice} -mindirect-branch-cs-prefix -mneeded -mno-direct-extern-access --munroll-only-small-loops -mlam=@var{choice}} +-munroll-only-small-loops -mlam=@var{choice} -malign-tight-loops} @emph{x86 Windows Options} @@ -36530,6 +36530,11 @@ LAM(linear-address masking) allows special bits in the pointer to be used for metadata. The default is @samp{none}. With @samp{u48}, pointer bits in positions 62:48 can be used for metadata; With @samp{u57}, pointer bits in positions 62:57 can be used for metadata. + +@opindex malign-tight-loops +@opindex mno-align-tight-loops +@item -malign-tight-loops +Controls tight loop alignment optimization. @end table @node x86 Windows Options
Hi all: This patch add -malign-tight-loops flag to control pass_align_tight_loops. The motivation is that pass_align_tight_loops may cause performance regression in nested loops. The example code as follows: #define ITER 20000 #define ITER_O 10 int i, j,k; int array[ITER]; void loop() { int i; for(k = 0; k < ITER_O; k++) for(j = 0; j < ITER; j++) for(i = 0; i < ITER; i++) { array[i] += j; array[i] += i; array[i] += 2*j; array[i] += 2*i; } } When I compile it with gcc -O1 loop.c, the output assembly as follows. It is not optimal, because of too many nops insert in the outer loop. 0000000000400540 <loop>: 400540: 48 83 ec 08 sub $0x8,%rsp 400544: bf 0a 00 00 00 mov $0xa,%edi 400549: b9 00 00 00 00 mov $0x0,%ecx 40054e: 8d 34 09 lea (%rcx,%rcx,1),%esi 400551: b8 00 00 00 00 mov $0x0,%eax 400556: 66 66 2e 0f 1f 84 00 data16 nopw %cs:0x0(%rax,%rax,1) 40055d: 00 00 00 00 400561: 66 66 2e 0f 1f 84 00 data16 nopw %cs:0x0(%rax,%rax,1) 400568: 00 00 00 00 40056c: 66 66 2e 0f 1f 84 00 data16 nopw %cs:0x0(%rax,%rax,1) 400573: 00 00 00 00 400577: 66 0f 1f 84 00 00 00 nopw 0x0(%rax,%rax,1) 40057e: 00 00 400580: 89 ca mov %ecx,%edx 400582: 03 14 85 60 10 60 00 add 0x601060(,%rax,4),%edx 400589: 01 c2 add %eax,%edx 40058b: 01 f2 add %esi,%edx 40058d: 8d 14 42 lea (%rdx,%rax,2),%edx 400590: 89 14 85 60 10 60 00 mov %edx,0x601060(,%rax,4) 400597: 48 83 c0 01 add $0x1,%rax 40059b: 48 3d 20 4e 00 00 cmp $0x4e20,%rax 4005a1: 75 dd jne 400580 <loop+0x40> I benchmark this program in the intel Xeon, and find the optimization may cause a 40% performance regression (6.6B cycles VS 9.3B cycles). So I propose to add -malign-tight-loops flag to control tight loop optimization to avoid this, we could disalbe this optimization by default. Bootstrapped X86_64. Ok for trunk? BR Mayshao gcc/ChangeLog: * config/i386/i386-features.cc (ix86_align_tight_loops): New flag. * config/i386/i386.opt (malign-tight-loops): New option. * doc/invoke.texi (-malign-tight-loops): Document. --- gcc/config/i386/i386-features.cc | 4 +++- gcc/config/i386/i386.opt | 4 ++++ gcc/doc/invoke.texi | 7 ++++++- 3 files changed, 13 insertions(+), 2 deletions(-)