digitalmars.D.bugs - [Issue 2008] New: Poor optimization of functions with ref parameters
- d-bugmail puremagic.com (55/55) Apr 18 2008 http://d.puremagic.com/issues/show_bug.cgi?id=2008
- d-bugmail puremagic.com (5/5) Apr 18 2008 http://d.puremagic.com/issues/show_bug.cgi?id=2008
- d-bugmail puremagic.com (57/57) May 15 2009 http://d.puremagic.com/issues/show_bug.cgi?id=2008
- d-bugmail puremagic.com (12/12) Jan 24 2010 http://d.puremagic.com/issues/show_bug.cgi?id=2008
- d-bugmail puremagic.com (10/13) Jan 24 2010 http://d.puremagic.com/issues/show_bug.cgi?id=2008
- d-bugmail puremagic.com (8/17) Jan 24 2010 http://d.puremagic.com/issues/show_bug.cgi?id=2008
- d-bugmail puremagic.com (15/15) May 09 2010 http://d.puremagic.com/issues/show_bug.cgi?id=2008
- d-bugmail puremagic.com (13/13) May 09 2010 http://d.puremagic.com/issues/show_bug.cgi?id=2008
- d-bugmail puremagic.com (59/59) May 09 2010 http://d.puremagic.com/issues/show_bug.cgi?id=2008
- d-bugmail puremagic.com (19/19) May 10 2010 http://d.puremagic.com/issues/show_bug.cgi?id=2008
- d-bugmail puremagic.com (10/10) May 16 2010 http://d.puremagic.com/issues/show_bug.cgi?id=2008
- d-bugmail puremagic.com (13/13) May 21 2010 http://d.puremagic.com/issues/show_bug.cgi?id=2008
http://d.puremagic.com/issues/show_bug.cgi?id=2008
Summary: Poor optimization of functions with ref parameters
Product: D
Version: 1.028
Platform: PC
OS/Version: Windows
Status: NEW
Severity: normal
Priority: P2
Component: DMD
AssignedTo: bugzilla digitalmars.com
ReportedBy: aarti interia.pl
Functions with ref parameters can be up to 2x slower than functions which
parameters are not passed by reference. It is especially visible for programs
which are compiled with all optimizations on:
-O
-inline
-release
Test program:
------------------------
char peek_ref(ref char[] a) {
return a[0];
}
char peek_noref(char[] a) {
return a[0];
}
ulong rdtsc() {
asm {
naked;
rdtsc;
ret;
}
}
void main() {
char[] tst = "test string";
char c;
long starttime;
writef("Direct: ");
starttime = rdtsc;
for(int i=0; i<1000; i++)
c = tst[0];
writefln(c, " - time: ", rdtsc - starttime);
writef("With ref: ");
starttime = rdtsc;
for(int i=0; i<1000; i++)
c = tst.peek_ref();
writefln(c, " - time: ", rdtsc - starttime);
writef("Without ref: ");
starttime = rdtsc;
for(int i=0; i<1000; i++)
c = tst.peek_noref();
writefln(c, " - time: ", rdtsc - starttime);
}
----------------------
--
Apr 18 2008
d-bugmail puremagic.com http://d.puremagic.com/issues/show_bug.cgi?id=2008 I believe the problem is that ref parameters disable inlining in DMD. Or so I think I heard somewhere before. --
Apr 18 2008
http://d.puremagic.com/issues/show_bug.cgi?id=2008
David Simcha <dsimcha yahoo.com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |dsimcha yahoo.com
---
This is true, and also applies to D2. Apparently ref prevents inlining. It's
somewhere in the comments in inline.c. Why, I don't know. The weird thing is
that apparently DMD inlines stuff with pointer parameters, and ref parameters
are just syntactic sugar for pointers. Here's a test program and the
disassembly.
import std.stdio;
// Shouldn't this generate *exactly* the same code as ptrSwap?
void swap(T)(ref T a, ref T b) {
T temp = a;
a = b;
b = temp;
}
void ptrSwap(T)(T* a, T* b) {
T temp = *a;
*a = *b;
*b = temp;
}
void main() {
uint a, b;
swap(a, b);
ptrSwap(&a, &b);
writeln(a); // Keep DMD from optimizing out ptrSwap entirely.
}
Here's the disassembly of the relevant portion:
COMDEF __Dmain
push eax ;
push eax ;
xor eax, eax ;
push ebx ;
lea ecx, [esp+4H] ;
mov dword ptr [esp+4H], eax ;
mov dword ptr [esp+8H], eax ;
push ecx ;
lea eax, [esp+0CH] ;
call _D5test711__T4swapTkZ4swapFKkKkZv ;
mov edx, dword ptr [esp+4H] ;
mov ebx, dword ptr [esp+8H] ;
mov dword ptr [esp+4H], ebx ;
mov eax, offset FLAT:_main ;
mov dword ptr [esp+8H], edx ;
push ebx ;
push 10 ;
call _D3std5stdio4File14__T5writeTkTaZ5writeMFkaZv;
xor eax, eax ;
pop ebx ;
add esp, 8 ;
ret ;
__Dmain ENDP
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May 15 2009
http://d.puremagic.com/issues/show_bug.cgi?id=2008
Eldar Insafutdinov <e.insafutdinov gmail.com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |e.insafutdinov gmail.com
09:39:04 PST ---
Recent change to dmd forced everybody to use opEquals with ref arguments. That
leaves no other option than the poorly optimised one. Isn't it time to fix this
bug?
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Jan 24 2010
http://d.puremagic.com/issues/show_bug.cgi?id=2008Recent change to dmd forced everybody to use opEquals with ref arguments. That leaves no other option than the poorly optimised one. Isn't it time to fix this bug?I think the more important fix is to start allowing opEquals with non-ref arguments again. Only allowing ref arguments is ridiculous because it forces the argument to be an lvalue, thus creating a horribly ugly inconsistency with builtin types. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Jan 24 2010
http://d.puremagic.com/issues/show_bug.cgi?id=2008 16:06:02 PST ---That's true. Perhaps functions with signature (const ref T) could accept rvalues as well, as the semantics is equivalent to (T)? -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------Recent change to dmd forced everybody to use opEquals with ref arguments. That leaves no other option than the poorly optimised one. Isn't it time to fix this bug?I think the more important fix is to start allowing opEquals with non-ref arguments again. Only allowing ref arguments is ridiculous because it forces the argument to be an lvalue, thus creating a horribly ugly inconsistency with builtin types.
Jan 24 2010
http://d.puremagic.com/issues/show_bug.cgi?id=2008
Brad Roberts <braddr puremagic.com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |ASSIGNED
AssignedTo|nobody puremagic.com |braddr puremagic.com
---
Created an attachment (id=626)
a potential patch (lots of debugging code left in for now)
This diff likely needs to be used in conjunction with the patch in bug 4149. I
haven't tested it separately to find out.
I also haven't tested it with more than the simple test case in bug 4149.
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May 09 2010
http://d.puremagic.com/issues/show_bug.cgi?id=2008 --- Testing with the code from Marcin, using -O -inline and fixing several bugs due to changes since 2008: Direct: t - time: 4319 With ref: t - time: 4319 Without ref: t - time: 4382 The code changes (not perfect, but enough to get it to compile): 1) add .dup to the "test string" literal 2) s/writefln/writeln/ -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
May 09 2010
http://d.puremagic.com/issues/show_bug.cgi?id=2008
---
Testing with David's code, with -O -inline, here's the new _Dmain:
_Dmain:
push EBP
mov EBP,ESP
mov EAX,offset
FLAT:_D3std5stdio6stdoutS3std5stdio4File SYM32
push 0
push 0Ah
call near ptr
_D3std5stdio4File14__T5writeTkTaZ5writeMFkaZv PC32
xor EAX,EAX
pop EBP
ret
Without -O:
_Dmain:
push EBP
mov EBP,ESP
sub ESP,024h
push EBX
push ESI
xor EAX,EAX
mov -024h[EBP],EAX
mov -020h[EBP],EAX
lea ECX,-024h[EBP]
mov -01Ch[EBP],ECX
lea EDX,-020h[EBP]
mov -018h[EBP],EDX
mov EBX,[ECX]
mov -014h[EBP],EBX
mov ESI,[EDX]
mov [ECX],ESI
mov [EDX],EBX
lea EAX,-024h[EBP]
mov -010h[EBP],EAX
lea ECX,-020h[EBP]
mov -0Ch[EBP],ECX
mov EDX,[EAX]
mov -8[EBP],EDX
mov EBX,[ECX]
mov [EAX],EBX
mov [ECX],EDX
mov ESI,-024h[EBP]
mov -4[EBP],ESI
push ESI
push 0Ah
mov EAX,offset
FLAT:_D3std5stdio6stdoutS3std5stdio4File SYM32
call near ptr
_D3std5stdio4File14__T5writeTkTaZ5writeMFkaZv PC32
xor EAX,EAX
pop ESI
pop EBX
leave
ret
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May 09 2010
http://d.puremagic.com/issues/show_bug.cgi?id=2008
Brad Roberts <braddr puremagic.com> changed:
What |Removed |Added
----------------------------------------------------------------------------
obsolete| |
---
Created an attachment (id=627)
Enable inlining of functions with ref parameters, v2
The previous patch didn't pass the dmd test suite (still need to understand
why).
This newer patch isolates the changes to the inlining code to generate AST
closer to what would be manually written for hand inlined code. I also dropped
all of the debugging code and unrelated code cleanup. This version DOES pass
the dmd test suite.
I've also confirmed that it is NOT dependent on the patch attached to bug 4149.
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May 10 2010
http://d.puremagic.com/issues/show_bug.cgi?id=2008 PDT --- Created an attachment (id=633) add support for out parameters as well (so both ref and out) The previous patch only added support for ref parameters. This updated patch also includes adding support for inlining of functions that have out parameters. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
May 16 2010
http://d.puremagic.com/issues/show_bug.cgi?id=2008
Walter Bright <bugzilla digitalmars.com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|ASSIGNED |RESOLVED
CC| |bugzilla digitalmars.com
Resolution| |FIXED
Severity|normal |enhancement
18:34:35 PDT ---
changeset 497. Does static arrays too.
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May 21 2010