[M3commit] CVS Update: cm3
Jay K
jay.krell at cornell.edu
Fri Jan 7 05:08:24 CET 2011
I don't think so, but maybe.
For i := 1 to 10 do try finally end
will run that generated code 10 times but only the 1st is needed. In general? I not sure.
Jay/phone
> Subject: Re: [M3commit] CVS Update: cm3
> From: hosking at cs.purdue.edu
> Date: Thu, 6 Jan 2011 16:56:48 -0500
> CC: m3commit at elegosoft.com
> To: jay.krell at cornell.edu
>
> You are confusing code emitted in the body of the loop with dynamic executions of that code.
> CG calls are all compile-time generation of code.
>
> On Jan 6, 2011, at 4:17 PM, Jay K wrote:
>
> >
> > If I have a try/finally or lock in a loop, those lines aren't going to guaranteeably store the same values each time?
> >
> > - Jay
> >
> > ----------------------------------------
> >> Subject: Re: [M3commit] CVS Update: cm3
> >> From: hosking at cs.purdue.edu
> >> Date: Thu, 6 Jan 2011 16:00:08 -0500
> >> CC: m3commit at elegosoft.com
> >> To: jay.krell at cornell.edu
> >>
> >> In the code below there are no initializations.
> >>
> >> On Jan 6, 2011, at 3:51 PM, Jay K wrote:
> >>
> >>>
> >>> ps: I think there other non-ideal initializations here.
> >>> e.g.
> >>>
> >>>
> >>> TryFinStmt.m3:Compile2
> >>> (* declare and initialize the info record *)
> >>> frame := CG.Declare_local (M3ID.NoID, M3RT.EF2_SIZE, Target.Address.align,
> >>> CG.Type.Struct, 0, in_memory := TRUE,
> >>> up_level := FALSE, f := CG.Never);
> >>> CG.Load_procedure (p.handler.cg_proc);
> >>> CG.Store_addr (frame, M3RT.EF2_handler);
> >>> CG.Load_static_link (p.handler.cg_proc);
> >>> CG.Store_addr (frame, M3RT.EF2_frame);
> >>>
> >>>
> >>> Putting TRY/LOCK in loops probably repeatedly does the same initializations.
> >>> Granted, this is non-stack-walker code.
> >>>
> >>> Seems all bit a suspicious to me, though I'm pretty ignorant of m3front still..
> >>>
> >>> - Jay
> >>>
> >>> ----------------------------------------
> >>>> From: jay.krell at cornell.edu
> >>>> To: hosking at cs.purdue.edu
> >>>> CC: m3commit at elegosoft.com
> >>>> Subject: RE: [M3commit] CVS Update: cm3
> >>>> Date: Thu, 6 Jan 2011 20:48:56 +0000
> >>>>
> >>>>
> >>>> The same way as before. I think this operates at too low a level to get any automatic initialization.
> >>>>
> >>>> TryStmt.m3 and TryFinStmt.m3:
> >>>>
> >>>> frame := CG.Declare_local (M3ID.NoID, M3RT.EF1_SIZE, Target.Address.align,
> >>>> CG.Type.Struct, 0, in_memory := TRUE,
> >>>> up_level := FALSE, f := CG.Never);
> >>>>
> >>>> I agree though, this might not be ideal.
> >>>>
> >>>> - Jay
> >>>>
> >>>>
> >>>> ----------------------------------------
> >>>>> Subject: Re: [M3commit] CVS Update: cm3
> >>>>> From: hosking at cs.purdue.edu
> >>>>> Date: Thu, 6 Jan 2011 15:42:33 -0500
> >>>>> CC: m3commit at elegosoft.com
> >>>>> To: jay.krell at cornell.edu
> >>>>>
> >>>>> I don't understand what you mean by "initializes to NIL".
> >>>>> How are you creating the frame variable?
> >>>>> If you do it properly the language semantics will cause it be initialized to NIL automatically.
> >>>>>
> >>>>> On Jan 6, 2011, at 3:33 PM, Jay K wrote:
> >>>>>
> >>>>>>
> >>>>>> Ok.
> >>>>>> Do you know where to initialize the jmpbuf to NIL?
> >>>>>>
> >>>>>> I have a diff that "works" (ie: doesn't crash) and is *close* to correct,
> >>>>>> it checks for NIL and branches around the alloca for non-NIL, but it
> >>>>>> also initializes to NIL repeatedly, so no change effectively.
> >>>>>>
> >>>>>>
> >>>>>> Index: misc/Marker.m3
> >>>>>> ===================================================================
> >>>>>> RCS file: /usr/cvs/cm3/m3-sys/m3front/src/misc/Marker.m3,v
> >>>>>> retrieving revision 1.7
> >>>>>> diff -u -w -r1.7 Marker.m3
> >>>>>> --- misc/Marker.m3 5 Jan 2011 14:34:54 -0000 1.7
> >>>>>> +++ misc/Marker.m3 6 Jan 2011 20:32:00 -0000
> >>>>>> @@ -233,6 +233,7 @@
> >>>>>>
> >>>>>> PROCEDURE CaptureState (frame: CG.Var; handler: CG.Label) =
> >>>>>> VAR new: BOOLEAN;
> >>>>>> + label := CG.Next_label ();
> >>>>>> BEGIN
> >>>>>> (* int setjmp(void* ); *)
> >>>>>> IF (setjmp = NIL) THEN
> >>>>>> @@ -263,18 +264,25 @@
> >>>>>> Target.Word.cg_type, 0);
> >>>>>> END;
> >>>>>>
> >>>>>> + (* IF frame.jmpbuf = NIL THEN *)
> >>>>>> +
> >>>>>> + CG.Load_nil ();
> >>>>>> + CG.Load_addr (frame, M3RT.EF1_jmpbuf);
> >>>>>> + CG.If_compare (Target.Address.cg_type, CG.Cmp.NE, label, CG.Maybe);
> >>>>>> +
> >>>>>> (* frame.jmpbuf = alloca(Csetjmp__Jumpbuf_size); *)
> >>>>>> CG.Start_call_direct (alloca, 0, Target.Address.cg_type);
> >>>>>> CG.Load_int (Target.Word.cg_type, Jumpbuf_size);
> >>>>>> CG.Pop_param (Target.Word.cg_type);
> >>>>>> CG.Call_direct (alloca, Target.Address.cg_type);
> >>>>>> - CG.Store (frame, M3RT.EF1_jmpbuf, Target.Address.size, Target.Address.align,
> >>>>>> - Target.Address.cg_type);
> >>>>>> + CG.Store_addr (frame, M3RT.EF1_jmpbuf);
> >>>>>> +
> >>>>>> + (* END *)
> >>>>>> + CG.Set_label (label);
> >>>>>>
> >>>>>> (* setmp(frame.jmpbuf) *)
> >>>>>> CG.Start_call_direct (setjmp, 0, Target.Integer.cg_type);
> >>>>>> - CG.Load (frame, M3RT.EF1_jmpbuf, Target.Address.size, Target.Address.align,
> >>>>>> - Target.Address.cg_type);
> >>>>>> + CG.Load_addr (frame, M3RT.EF1_jmpbuf);
> >>>>>> CG.Pop_param (CG.Type.Addr);
> >>>>>> CG.Call_direct (setjmp, Target.Integer.cg_type);
> >>>>>> CG.If_true (handler, CG.Never);
> >>>>>> cvs diff: Diffing stmts
> >>>>>> Index: stmts/TryFinStmt.m3
> >>>>>> ===================================================================
> >>>>>> RCS file: /usr/cvs/cm3/m3-sys/m3front/src/stmts/TryFinStmt.m3,v
> >>>>>> retrieving revision 1.6
> >>>>>> diff -u -w -r1.6 TryFinStmt.m3
> >>>>>> --- stmts/TryFinStmt.m3 5 Jan 2011 14:34:54 -0000 1.6
> >>>>>> +++ stmts/TryFinStmt.m3 6 Jan 2011 20:32:00 -0000
> >>>>>> @@ -299,6 +299,10 @@
> >>>>>> CG.Load_nil ();
> >>>>>> CG.Store_addr (frame, M3RT.EF1_info + M3RT.EA_exception);
> >>>>>>
> >>>>>> + (* no jmpbuf yet (avoid repeated alloca in try within loop) *)
> >>>>>> + CG.Load_nil ();
> >>>>>> + CG.Store_addr (frame, M3RT.EF1_jmpbuf);
> >>>>>> +
> >>>>>> l := CG.Next_label (3);
> >>>>>> CG.Set_label (l, barrier := TRUE);
> >>>>>> Marker.PushFrame (frame, M3RT.HandlerClass.Finally);
> >>>>>> Index: stmts/TryStmt.m3
> >>>>>> ===================================================================
> >>>>>> RCS file: /usr/cvs/cm3/m3-sys/m3front/src/stmts/TryStmt.m3,v
> >>>>>> retrieving revision 1.3
> >>>>>> diff -u -w -r1.3 TryStmt.m3
> >>>>>> --- stmts/TryStmt.m3 5 Jan 2011 14:34:54 -0000 1.3
> >>>>>> +++ stmts/TryStmt.m3 6 Jan 2011 20:32:00 -0000
> >>>>>> @@ -10,7 +10,7 @@
> >>>>>>
> >>>>>> IMPORT M3, M3ID, CG, Variable, Scope, Exceptionz, Value, Error, Marker;
> >>>>>> IMPORT Type, Stmt, StmtRep, TryFinStmt, Token;
> >>>>>> -IMPORT Scanner, ESet, Target, M3RT, Tracer;
> >>>>>> +IMPORT Scanner, ESet, Target, M3RT, Tracer, IO;
> >>>>>> FROM Scanner IMPORT Match, MatchID, GetToken, Fail, cur;
> >>>>>>
> >>>>>> TYPE
> >>>>>> @@ -411,6 +411,10 @@
> >>>>>> CG.Store_addr (frame, M3RT.EF1_exception);
> >>>>>> ***********************************************)
> >>>>>>
> >>>>>> + (* no jmpbuf yet (avoid repeated alloca in try within loop) *)
> >>>>>> + CG.Load_nil ();
> >>>>>> + CG.Store_addr (frame, M3RT.EF1_jmpbuf);
> >>>>>> +
> >>>>>> IF (p.hasElse) THEN
> >>>>>> Marker.PushTryElse (l, l+1, frame);
> >>>>>> Marker.PushFrame (frame, M3RT.HandlerClass.ExceptElse);
> >>>>>>
> >>>>>>
> >>>>>> The set_label before one of the PushEFrames could be moved down a bit,
> >>>>>> to after the NIL initialization, and that'd fix some cases, but I think not all.
> >>>>>>
> >>>>>> Thanks,
> >>>>>> - Jay
> >>>>>>
> >>>>>>
> >>>>>> ----------------------------------------
> >>>>>>> Subject: Re: [M3commit] CVS Update: cm3
> >>>>>>> From: hosking at cs.purdue.edu
> >>>>>>> Date: Thu, 6 Jan 2011 14:11:04 -0500
> >>>>>>> CC: m3commit at elegosoft.com
> >>>>>>> To: jay.krell at cornell.edu
> >>>>>>>
> >>>>>>> At this point, we are trying to move away from the setjmp implementation to one that relies on unwind support, so I don't think the effort here is worthwhile.
> >>>>>>>
> >>>>>>> Antony Hosking | Associate Professor | Computer Science | Purdue University
> >>>>>>> 305 N. University Street | West Lafayette | IN 47907 | USA
> >>>>>>> Office +1 765 494 6001 | Mobile +1 765 427 5484
> >>>>>>>
> >>>>>>>
> >>>>>>>
> >>>>>>>
> >>>>>>> On Jan 6, 2011, at 2:00 PM, Jay K wrote:
> >>>>>>>
> >>>>>>>>
> >>>>>>>> I believe you can, but it'd take significant work in the frontend.
> >>>>>>>> The jmpbuf should identify merely which procedure/frame to return to.
> >>>>>>>> There would also be a volatile local integer, that gets altered at certain points through the function.
> >>>>>>>> When setjmp returns exceptionally, you'd switch on that integer to determine where to "really" go.
> >>>>>>>> This is analogous to how other systems work -- NT/x86 has a highly optimized frame based exception
> >>>>>>>> handling. Instead of a generic thread local, FS:0 is reserved to be the head of the linked list of frames.
> >>>>>>>> Instead of setjmp, the compiler pessimizes appropriately.
> >>>>>>>>
> >>>>>>>>
> >>>>>>>> So the result is that a function with one or more tries, or one or more locals with destructors,
> >>>>>>>> puts one node on the FS:0 list, and then mucks with the volatile local integer to indicate
> >>>>>>>> where in the function it is.
> >>>>>>>>
> >>>>>>>>
> >>>>>>>> If NT/x86 were inefficient more analogous to current Modula-3, it'd link/unlink in FS:0 more often.
> >>>>>>>>
> >>>>>>>>
> >>>>>>>> It is more work through, granted, I can understand that.
> >>>>>>>> And given that we have a much better option for many platforms, the payoff would be reduced.
> >>>>>>>>
> >>>>>>>>
> >>>>>>>> Anyway, I'm trying what you say, like for TRY within a loop.
> >>>>>>>>
> >>>>>>>>
> >>>>>>>> I should point out that alloca has an extra inefficiency vs. the previous approach.
> >>>>>>>> It aligns more. So it is using more stack than the other way.
> >>>>>>>> And it might pessimize codegen in other ways.
> >>>>>>>>
> >>>>>>>>
> >>>>>>>> The gcc code appears somewhat similar..I think the tables merely describe, again, which
> >>>>>>>> function/frame to return to, and that within the frame there is a local integer to determine
> >>>>>>>> more precisely what to do. I'm not sure. I saw mention of a switch.
> >>>>>>>>
> >>>>>>>>
> >>>>>>>> - Jay
> >>>>>>>>
> >>>>>>>> ________________________________
> >>>>>>>>> Subject: Re: [M3commit] CVS Update: cm3
> >>>>>>>>> From: hosking at cs.purdue.edu
> >>>>>>>>> Date: Thu, 6 Jan 2011 13:52:42 -0500
> >>>>>>>>> CC: m3commit at elegosoft.com
> >>>>>>>>> To: jay.krell at cornell.edu
> >>>>>>>>>
> >>>>>>>>> You can't have one jmpbuf per procedure. You need one per TRY scope,
> >>>>>>>>> since they can be nested.
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> On Jan 6, 2011, at 11:35 AM, Jay K wrote:
> >>>>>>>>>
> >>>>>>>>> Hm. How do I single instance the "EF1"? The current code allocates a
> >>>>>>>>> local "EF1" for each try.
> >>>>>>>>> I guess, really, it is EF1, EF2, etc.
> >>>>>>>>> So there should be a separate local for the jmpbuf pointer, and store
> >>>>>>>>> it in each EF* block?
> >>>>>>>>> How do I make just one jmpbuf pointer? I couldn't easily figure out how
> >>>>>>>>> to in the front end, I need to read it more.
> >>>>>>>>>
> >>>>>>>>> something like:
> >>>>>>>>>
> >>>>>>>>> PROCEDURE F1() = BEGIN TRY1 do stuff1 TRY2 do stuff 2 TRY3 do stuff 3
> >>>>>>>>> END END END END F1;
> >>>>>>>>> =>
> >>>>>>>>>
> >>>>>>>>> void F1()
> >>>>>>>>> {
> >>>>>>>>> jmp_buf* jb = 0;
> >>>>>>>>> EF1 a,b,c;
> >>>>>>>>> setjmp(a.jmpbuf = jb ? jb : (jb = alloca(sizeof(jmp_buf))); // TRY1
> >>>>>>>>> do stuff 1...
> >>>>>>>>> setjmp(b.jmpbuf = jb ? jb : (jb = alloca(sizeof(jmp_buf))); // TRY2
> >>>>>>>>> do stuff 2...
> >>>>>>>>> setjmp(c.jmpbuf = jb ? jb : (jb = alloca(sizeof(jmp_buf))); // TRY3
> >>>>>>>>> do stuff 3...
> >>>>>>>>> }
> >>>>>>>>>
> >>>>>>>>> (The actual syntactic and semantic correctness of this code -- the
> >>>>>>>>> existance of the ternary operator, and that it only evaluates one side
> >>>>>>>>> or the other, and that assignment is expression..I quite like those
> >>>>>>>>> features....)
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> Still, something I can't pin down strikes me as too simple here.
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> If there is just one setjmp, and no integer(s) to keep track of
> >>>>>>>>> additional progress, you only ever know the last place you were in a
> >>>>>>>>> function.
> >>>>>>>>> That doesn't seem adequate.
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> What if a function raises an exception, catches it within itself, and
> >>>>>>>>> then raises something else, and then wants to catch that?
> >>>>>>>>> It won't know where to resume, right? It's just keep longjmping to the
> >>>>>>>>> same place.
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> In the Visual C++ runtime, there is "local unwind" and "global unwind".
> >>>>>>>>> "local unwind" is like, "within the same functin", "global unwind" is
> >>>>>>>>> across functions.
> >>>>>>>>> I think somehow that is related here.
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> e.g. how would you ensure forward progress in this:
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> EXCEPTION E1;
> >>>>>>>>> EXCEPTION E2;
> >>>>>>>>> EXCEPTION E3;
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> PROCEDURE F4() RAISES ANY =
> >>>>>>>>> CONST Function = "F4 ";
> >>>>>>>>> BEGIN
> >>>>>>>>> Put(Function & Int(Line())); NL();
> >>>>>>>>> TRY
> >>>>>>>>> Put(Function & Int(Line())); NL();
> >>>>>>>>> TRY
> >>>>>>>>> Put(Function & Int(Line())); NL();
> >>>>>>>>> TRY
> >>>>>>>>> Put(Function & Int(Line())); NL();
> >>>>>>>>> RAISE E1;
> >>>>>>>>> EXCEPT ELSE
> >>>>>>>>> RAISE E2;
> >>>>>>>>> END;
> >>>>>>>>> EXCEPT ELSE
> >>>>>>>>> RAISE E3;
> >>>>>>>>> END;
> >>>>>>>>> EXCEPT ELSE
> >>>>>>>>> END;
> >>>>>>>>> END F4;
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> Oddly in my test p251, the stack depth is not increased by TRY.
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> - Jay
> >>>>>>>>>
> >>>>>>>>> ________________________________
> >>>>>>>>> Subject: Re: [M3commit] CVS Update: cm3
> >>>>>>>>> From: hosking at cs.purdue.edu
> >>>>>>>>> Date: Thu, 6 Jan 2011 09:22:09 -0500
> >>>>>>>>> CC: m3commit at elegosoft.com
> >>>>>>>>> To: jay.krell at cornell.edu
> >>>>>>>>>
> >>>>>>>>> I am OK with what you have currently:
> >>>>>>>>>
> >>>>>>>>> At each TRY:
> >>>>>>>>>
> >>>>>>>>> 1. Check if a corresponding alloca block has been allocated by checking
> >>>>>>>>> if the corresponding local variable is NIL.
> >>>>>>>>> 2. If not, then alloca and save its pointer in the local variable
> >>>>>>>>> 3. Execute the try block.
> >>>>>>>>>
> >>>>>>>>> As you say, alloca should turn into an inline operation using the
> >>>>>>>>> compiler's builtin implementation of alloca.
> >>>>>>>>>
> >>>>>>>>> On Jan 6, 2011, at 1:02 AM, Jay K wrote:
> >>>>>>>>>
> >>>>>>>>>> Code size will suffer.
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> Indeed. Unoptimized code size does suffer a lot, in functions that use try.
> >>>>>>>>> Calling alloca, unoptimized, isn't small, and this adds n calls for n trys.
> >>>>>>>>> I thought it'd only be one call. I didn't realize our implementation
> >>>>>>>>> is as poor as it is, since a better but still
> >>>>>>>>> portable implementation doesn't seem too too difficult.
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> Can we maybe do the optimizations I indicate -- no more than one
> >>>>>>>>> setjmp/alloca/pushframe per function?
> >>>>>>>>> Using a local integer to record the position within the function?
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> Or just give me a week or few to get stack walking working and then
> >>>>>>>>> live the regression on other targets?
> >>>>>>>>> (NT386 isn't likely to get stack walking, though it *is* certainly
> >>>>>>>>> possible; NT does have a decent runtime here..)
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> It *is* nice to not have have the frontend know about jmpbuf size.
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> I looked into the "builtin_setjmp" stuff, but it can't be used so easily.
> >>>>>>>>> It doesn't work for intra-function jumps, only inter-function.
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> - Jay
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> ________________________________
> >>>>>>>>> From: jay.krell at cornell.edu
> >>>>>>>>> To: hosking at cs.purdue.edu
> >>>>>>>>> CC: m3commit at elegosoft.com
> >>>>>>>>> Subject: RE: [M3commit] CVS Update: cm3
> >>>>>>>>> Date: Thu, 6 Jan 2011 04:52:33 +0000
> >>>>>>>>>
> >>>>>>>>> Ah..I'm doing more comparisons of release vs. head...but..I guess your
> >>>>>>>>> point is, you'd rather have n locals, which the backend automatically
> >>>>>>>>> merges, than n calls to alloca?
> >>>>>>>>> It's not a huge difference -- there are still going to be n calls to
> >>>>>>>>> setjmp and n calls to pthread_getspecific.
> >>>>>>>>> The alloca calls will be dwarfed.
> >>>>>>>>> Code size will suffer.
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> And, even so, there are plenty of optimizations to be had, even if
> >>>>>>>>> setjmp/pthread_getspecific is used.
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> - It could make a maximum of one call to setjmp/pthread_getspecific
> >>>>>>>>> per function
> >>>>>>>>> - The calls to alloca could be merged. The frontend could keep track
> >>>>>>>>> of how many calls it makes per function,
> >>>>>>>>> issue a multiplication, and offset each jmpbuf. It is a tradeoff.
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> So, yes, given my current understanding, it is progress.
> >>>>>>>>> The target-dependence is not worth it, imho.
> >>>>>>>>> I'll still do some comparisons to release.
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> I'll still be looking into using the gcc unwinder relatively soon.
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> - Jay
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> ________________________________
> >>>>>>>>> Subject: Re: [M3commit] CVS Update: cm3
> >>>>>>>>> From: hosking at cs.purdue.edu
> >>>>>>>>> Date: Wed, 5 Jan 2011 21:14:17 -0500
> >>>>>>>>> CC: m3commit at elegosoft.com
> >>>>>>>>> To: jay.krell at cornell.edu
> >>>>>>>>>
> >>>>>>>>> On Jan 5, 2011, at 9:08 PM, Jay K wrote:
> >>>>>>>>>
> >>>>>>>>> Tony, um..well, um.. first, isn't that how it already worked maybe?
> >>>>>>>>> Declaring a new local EF1 for each TRY? It looks like it.
> >>>>>>>>> I'll do more testing.
> >>>>>>>>>
> >>>>>>>>> Yes, it did. I assume you simply have a local variable for each TRY
> >>>>>>>>> block that is a pointer now instead of a jmp_buf. Should be OK.
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> So the additional inefficiency is multiplied the same as the rest of
> >>>>>>>>> the preexisting inefficiency.
> >>>>>>>>> And the preexisting inefficiency is way more than the increase.
> >>>>>>>>>
> >>>>>>>>> And second, either way, it could be better.
> >>>>>>>>>
> >>>>>>>>> Basically, the model should be, that if a function has any try or lock,
> >>>>>>>>> it calls setjmp once.
> >>>>>>>>> And then, it should have one volatile integer, that in a sense
> >>>>>>>>> represents the line number.
> >>>>>>>>> But not really. It's like, every time you cross a TRY, the integer is
> >>>>>>>>> incremented, every time you
> >>>>>>>>> cross a finally or unlock, the integer is decremented. Or rather, the
> >>>>>>>>> value can be stored.
> >>>>>>>>> And then there is a maximum of one one handler per function, it
> >>>>>>>>> switches on the integer
> >>>>>>>>> to decide where it got into the function and what it should do.
> >>>>>>>>>
> >>>>>>>>> This is how other compilers work and it is a fairly simple sensible approach.
> >>>>>>>>>
> >>>>>>>>> - Jay
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> ________________________________
> >>>>>>>>> Subject: Re: [M3commit] CVS Update: cm3
> >>>>>>>>> From: hosking at cs.purdue.edu
> >>>>>>>>> Date: Wed, 5 Jan 2011 20:49:24 -0500
> >>>>>>>>> CC: m3commit at elegosoft.com
> >>>>>>>>> To: jay.krell at cornell.edu
> >>>>>>>>>
> >>>>>>>>> Note that you need a different jmpbuf for each nested TRY!
> >>>>>>>>>
> >>>>>>>>> Antony Hosking | Associate Professor | Computer Science | Purdue University
> >>>>>>>>> 305 N. University Street | West Lafayette | IN 47907 | USA
> >>>>>>>>> Office +1 765 494 6001 | Mobile +1 765 427 5484
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> On Jan 5, 2011, at 8:33 PM, Jay K wrote:
> >>>>>>>>>
> >>>>>>>>> oops, that's not how I thought it worked. I'll do more testing and fix
> >>>>>>>>> it -- check for NIL.
> >>>>>>>>>
> >>>>>>>>> - Jay
> >>>>>>>>>
> >>>>>>>>> ________________________________
> >>>>>>>>> Subject: Re: [M3commit] CVS Update: cm3
> >>>>>>>>> From: hosking at cs.purdue.edu
> >>>>>>>>> Date: Wed, 5 Jan 2011 20:23:09 -0500
> >>>>>>>>> CC: m3commit at elegosoft.com
> >>>>>>>>> To: jay.krell at cornell.edu
> >>>>>>>>>
> >>>>>>>>> Ah, yes, I guess you need a different jmpbuf for each TRY. But now you
> >>>>>>>>> are allocating on every TRY where previously the storage was statically
> >>>>>>>>> allocated. Do you really think this is progress?
> >>>>>>>>>
> >>>>>>>>> On Jan 5, 2011, at 5:40 PM, Jay K wrote:
> >>>>>>>>>
> >>>>>>>>> I've back with full keyboard if more explanation needed. The diff is
> >>>>>>>>> actually fairly small to read.
> >>>>>>>>> I understand it is definitely less efficient, a few more instructions
> >>>>>>>>> for every try/lock.
> >>>>>>>>> No extra function call, at least with gcc backend.
> >>>>>>>>> I haven't tested NT386 yet. Odds are so/so that it works -- the change
> >>>>>>>>> is written so that it should work
> >>>>>>>>> but I have to test it to be sure, will to roughly tonight. And there
> >>>>>>>>> probably is a function call there.
> >>>>>>>>>
> >>>>>>>>> - Jay
> >>>>>>>>>
> >>>>>>>>> ________________________________
> >>>>>>>>> From: jay.krell at cornell.edu
> >>>>>>>>> To: hosking at cs.purdue.edu
> >>>>>>>>> Date: Wed, 5 Jan 2011 20:44:08 +0000
> >>>>>>>>> CC: m3commit at elegosoft.com
> >>>>>>>>> Subject: Re: [M3commit] CVS Update: cm3
> >>>>>>>>>
> >>>>>>>>> I only have phone right now. I think it is fairly clear: the jumpbuf in
> >>>>>>>>> EF1 is now allocated with alloca, and a pointer stored. It is
> >>>>>>>>> definitely a bit less efficient, but the significant advantage is
> >>>>>>>>> frontend no longer needs to know the size or alignment of a jumpbuf.
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> As well, there is no longer the problem regarding jumpbuf aligned to
> >>>>>>>>> more than 64 bits. I at least checked on Linux/PowerPC and alloca seems
> >>>>>>>>> to align to 16 bytes. I don't have an HPUX machine currently to see if
> >>>>>>>>> the problem is addressed there.
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> The inefficiency of course can be dramatically mitigated via a stack
> >>>>>>>>> walker. I wanted to do this first though, while more targets using
> >>>>>>>>> setjmp.
> >>>>>>>>>
> >>>>>>>>> - Jay/phone
> >>>>>>>>>
> >>>>>>>>> ________________________________
> >>>>>>>>> Subject: Re: [M3commit] CVS Update: cm3
> >>>>>>>>> From: hosking at cs.purdue.edu
> >>>>>>>>> Date: Wed, 5 Jan 2011 13:35:59 -0500
> >>>>>>>>> CC: jkrell at elego.de; m3commit at elegosoft.com
> >>>>>>>>> To: jay.krell at cornell.edu
> >>>>>>>>>
> >>>>>>>>> Can you provide a more descriptive checkin comment? I don't know what
> >>>>>>>>> has been done here without diving into the diff.
> >>>>>>>>>
> >>>>>>>>> Antony Hosking | Associate Professor | Computer Science | Purdue University
> >>>>>>>>> 305 N. University Street | West Lafayette | IN 47907 | USA
> >>>>>>>>> Office +1 765 494 6001 | Mobile +1 765 427 5484
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> On Jan 5, 2011, at 9:37 AM, Jay K wrote:
> >>>>>>>>>
> >>>>>>>>> diff attached
> >>>>>>>>>
> >>>>>>>>>> Date: Wed, 5 Jan 2011 15:34:55 +0000
> >>>>>>>>>> To: m3commit at elegosoft.com
> >>>>>>>>>> From: jkrell at elego.de
> >>>>>>>>>> Subject: [M3commit] CVS Update: cm3
> >>>>>>>>>>
> >>>>>>>>>> CVSROOT: /usr/cvs
> >>>>>>>>>> Changes by: jkrell at birch. 11/01/05 15:34:55
> >>>>>>>>>>
> >>>>>>>>>> Modified files:
> >>>>>>>>>> cm3/m3-libs/m3core/src/C/Common/: Csetjmp.i3
> >>>>>>>>>> cm3/m3-libs/m3core/src/C/I386_CYGWIN/: Csetjmp.i3
> >>>>>>>>>> cm3/m3-libs/m3core/src/C/I386_MINGW/: Csetjmp.i3
> >>>>>>>>>> cm3/m3-libs/m3core/src/C/I386_NT/: Csetjmp.i3
> >>>>>>>>>> cm3/m3-libs/m3core/src/C/NT386/: Csetjmp.i3
> >>>>>>>>>> cm3/m3-libs/m3core/src/runtime/ex_frame/: RTExFrame.m3
> >>>>>>>>>> cm3/m3-libs/m3core/src/unix/Common/: Uconstants.c
> >>>>>>>>>> cm3/m3-sys/m3cc/gcc/gcc/m3cg/: parse.c
> >>>>>>>>>> cm3/m3-sys/m3front/src/misc/: Marker.m3
> >>>>>>>>>> cm3/m3-sys/m3front/src/stmts/: TryFinStmt.m3 TryStmt.m3
> >>>>>>>>>> cm3/m3-sys/m3middle/src/: M3RT.i3 M3RT.m3 Target.i3 Target.m3
> >>>>>>>>>>
> >>>>>>>>>> Log message:
> >>>>>>>>>> use: extern INTEGER Csetjmp__Jumpbuf_size /* = sizeof(jmp_buf);
> >>>>>>>>>> alloca(Csetjmp__Jumpbuf_size)
> >>>>>>>>>>
> >>>>>>>>>> to allocate jmp_buf
> >>>>>>>>>>
> >>>>>>>>>> - eliminates a large swath of target-dependent code
> >>>>>>>>>> - allows for covering up the inability to declare
> >>>>>>>>>> types with alignment > 64 bits
> >>>>>>>>>>
> >>>>>>>>>> It is, granted, a little bit slower, in an already prety slow path.
> >>>>>>>>>> Note that alloca isn't actually a function call, at least with gcc backend.
> >>>>>>>>>>
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>
> >>>>>>>
> >>>>>>
> >>>>>
> >>>>
> >>>
> >>
> >
>
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