digitalmars.D.ldc - fabs not being inlined?

NaN (24/24) Feb 07 2019 module ohreally;

David Nadlinger (7/8) Feb 07 2019 Try -enable-cross-module-inlining, or use link-time optimization. If

kinke (5/11) Feb 07 2019 Be sure to use `-flto=` *and*

NaN (9/19) Feb 08 2019 Performing "release" build using ldc2 for x86_64.

NaN (6/9) Feb 07 2019 That worked!
NaN (6/15) Feb 08 2019 Ok spoke to soon, went to bed after just testing it on godbolt,

9il (4/28) Feb 08 2019 Try also mir-core DUB package. It has mir.math package, fabs will
Guillaume Piolat (4/5) Feb 08 2019 Alternative: inline by hand

NaN (5/11) Feb 09 2019 This might not be pretty but it coaxes LDC to do abs with a

kinke (13/22) Feb 09 2019 Both manual versions are ugly and IMO should be avoided at all

Stefan Koch (3/19) Feb 11 2019 IIRC __chkstk is a msvcrt call to dynamically grow the stack.

Radu (3/7) Feb 11 2019 A good explanation on this:

kinke (4/12) Feb 12 2019 I wanted to spare you the details, but that's the workaround

NaN <divide by.zero> writes:

module ohreally;

import std.math;

float foo(float y, float x)
{
     float ax = fabs(x);
     float ay = fabs(y);
     return ax*ay/3.142f;
}

====>

float ohreally.foo(float, float):
         push    rax
         movss   dword ptr [rsp + 4], xmm1
         call    pure nothrow  nogc  safe float 
std.math.fabs(float) PLT
         movss   dword ptr [rsp], xmm0
         movss   xmm0, dword ptr [rsp + 4]
         call    pure nothrow  nogc  safe float 
std.math.fabs(float) PLT
         mulss   xmm0, dword ptr [rsp]
         divss   xmm0, dword ptr [rip + .LCPI0_0]
         pop     rax
         ret

Compiled with -O3

Is there something I need to do to get fabs() inlined?

Feb 07 2019

"David Nadlinger" <code klickverbot.at> writes:

On 7 Feb 2019, at 23:26, NaN via digitalmars-d-ldc wrote:
 Is there something I need to do to get fabs() inlined?

Try -enable-cross-module-inlining, or use link-time optimization. If 
there isn't already, we should probably create a tracker bug for making 
sure we fix inlining for these, whether by switching cross-module 
inlining on by default again, or implementing/adding `pragma(inline, 
true)` to all the math shims.

  — David

Feb 07 2019

kinke <noone nowhere.com> writes:

On Thursday, 7 February 2019 at 23:50:10 UTC, David Nadlinger 
wrote:
 or use link-time optimization

Be sure to use `-flto=<thin|full>` *and* 
`-defaultlib=druntime-ldc-lto,phobos2-ldc-lto`.

 If there isn't already, we should probably create a tracker bug 
 for making sure we fix inlining for these, whether by switching 
 cross-module inlining on by default again, or 
 implementing/adding `pragma(inline, true)` to all the math 
 shims.

https://github.com/ldc-developers/ldc/issues/2552

Feb 07 2019

NaN <divide by.zero> writes:

On Friday, 8 February 2019 at 00:01:58 UTC, kinke wrote:
 On Thursday, 7 February 2019 at 23:50:10 UTC, David Nadlinger 
 wrote:
 or use link-time optimization

 Be sure to use `-flto=<thin|full>` *and* 
 `-defaultlib=druntime-ldc-lto,phobos2-ldc-lto`.

Ok tried that too, it results in ==>

 Executing task: dub run --compiler=ldc2 --build=release 
 --arch=x86_64 <

Performing "release" build using ldc2 for x86_64.
sonijit ~master: building configuration "application"...
lld-link.exe: error: undefined symbol: __chkstk
 referenced by lto.tmp:(_d_run_main)
 referenced by lto.tmp:(_d_run_main)
 referenced by lto.tmp:(_d_run_main)



Error: C:\LDC\bin\lld-link.exe failed with status: 1
ldc2 failed with exit code 1.
The terminal process terminated with exit code: 2

Terminal will be reused by tasks, press any key to close it.

Feb 08 2019

NaN <divide by.zero> writes:

On Thursday, 7 February 2019 at 23:50:10 UTC, David Nadlinger 
wrote:
 On 7 Feb 2019, at 23:26, NaN via digitalmars-d-ldc wrote:
 Is there something I need to do to get fabs() inlined?

 Try -enable-cross-module-inlining,

That worked!

I did look at

https://wiki.dlang.org/Using_LDC

but didnt see any reference to cross module inlining.

Feb 07 2019

NaN <divide by.zero> writes:

On Thursday, 7 February 2019 at 23:50:10 UTC, David Nadlinger 
wrote:
 On 7 Feb 2019, at 23:26, NaN via digitalmars-d-ldc wrote:
 Is there something I need to do to get fabs() inlined?

 Try -enable-cross-module-inlining, or use link-time 
 optimization. If there isn't already, we should probably create 
 a tracker bug for making sure we fix inlining for these, 
 whether by switching cross-module inlining on by default again, 
 or implementing/adding `pragma(inline, true)` to all the math 
 shims.

  — David

Ok spoke to soon, went to bed after just testing it on godbolt, 
but if I add that to my project the exe just hangs, opens a 
command window but nothing else. Is there any point we trying to 
figure out why or is it a known problem?

Feb 08 2019

9il <ilyayaroshenko gmail.com> writes:

On Thursday, 7 February 2019 at 23:26:20 UTC, NaN wrote:
 module ohreally;

 import std.math;

 float foo(float y, float x)
 {
     float ax = fabs(x);
     float ay = fabs(y);
     return ax*ay/3.142f;
 }

 ====>

 float ohreally.foo(float, float):
         push    rax
         movss   dword ptr [rsp + 4], xmm1
         call    pure nothrow  nogc  safe float 
 std.math.fabs(float) PLT
         movss   dword ptr [rsp], xmm0
         movss   xmm0, dword ptr [rsp + 4]
         call    pure nothrow  nogc  safe float 
 std.math.fabs(float) PLT
         mulss   xmm0, dword ptr [rsp]
         divss   xmm0, dword ptr [rip + .LCPI0_0]
         pop     rax
         ret

 Compiled with -O3

 Is there something I need to do to get fabs() inlined?

Try also mir-core DUB package. It has mir.math package, fabs will 
be inlined in -O builds without any additional flags.
http://code.dlang.org/packages/mir-core

Feb 08 2019

Guillaume Piolat <first.last gmail.com> writes:

On Thursday, 7 February 2019 at 23:26:20 UTC, NaN wrote:
 Is there something I need to do to get fabs() inlined?

Alternative: inline by hand

https://godbolt.org/z/DS0XIb

Works since LDC 1.0.0 -O1

Feb 08 2019

NaN <divide by.zero> writes:

On Friday, 8 February 2019 at 14:47:20 UTC, Guillaume Piolat 
wrote:
 On Thursday, 7 February 2019 at 23:26:20 UTC, NaN wrote:
 Is there something I need to do to get fabs() inlined?

 Alternative: inline by hand

 https://godbolt.org/z/DS0XIb

 Works since LDC 1.0.0 -O1

This might not be pretty but it coaxes LDC to do abs with a 
single instruction...

https://godbolt.org/z/0aVvSR

Feb 09 2019

kinke <noone nowhere.com> writes:

On Saturday, 9 February 2019 at 15:08:22 UTC, NaN wrote:
 On Friday, 8 February 2019 at 14:47:20 UTC, Guillaume Piolat 
 wrote:
 Alternative: inline by hand

 https://godbolt.org/z/DS0XIb

 This might not be pretty but it coaxes LDC to do abs with a 
 single instruction...

 https://godbolt.org/z/0aVvSR

Both manual versions are ugly and IMO should be avoided at all 
costs. ;) If LTO/cross-module-inlining is not an option but fabs 
performance is critical, then use the intrinsic directly:

import ldc.intrinsics;
alias fabs = llvm_fabs;

The reason std.math doesn't just alias (I had a go at this once) 
is that there are some tests checking that the std.math functions 
are real functions (and that their address can be taken).

 lld-link.exe: error: undefined symbol: __chkstk

Looks like some linker tricks required for the MinGW-based libs 
don't work with LTO; I guess it works with the MS toolchain, 
e.g., when run inside in a Visual Studio command prompt. I'll 
spare you the dirty details.

Feb 09 2019

Stefan Koch <uplink.coder googlemail.com> writes:

On Saturday, 9 February 2019 at 15:38:55 UTC, kinke wrote:
 On Saturday, 9 February 2019 at 15:08:22 UTC, NaN wrote:
 [...]

 Both manual versions are ugly and IMO should be avoided at all 
 costs. ;) If LTO/cross-module-inlining is not an option but 
 fabs performance is critical, then use the intrinsic directly:

 import ldc.intrinsics;
 alias fabs = llvm_fabs;

 The reason std.math doesn't just alias (I had a go at this 
 once) is that there are some tests checking that the std.math 
 functions are real functions (and that their address can be 
 taken).

 [...]

 Looks like some linker tricks required for the MinGW-based libs 
 don't work with LTO; I guess it works with the MS toolchain, 
 e.g., when run inside in a Visual Studio command prompt. I'll 
 spare you the dirty details.

IIRC __chkstk is a msvcrt call to dynamically grow the stack.
There might be a hidden dependency introduced by llvm?

Feb 11 2019

Radu <void null.pt> writes:

On Monday, 11 February 2019 at 23:52:50 UTC, Stefan Koch wrote:
 On Saturday, 9 February 2019 at 15:38:55 UTC, kinke wrote:
 [...]

 IIRC __chkstk is a msvcrt call to dynamically grow the stack.
 There might be a hidden dependency introduced by llvm?

A good explanation on this:
https://metricpanda.com/rival-fortress-update-45-dealing-with-__chkstk-__chkstk_ms-when-cross-compiling-for-windows

Feb 11 2019

kinke <noone nowhere.com> writes:

On Tuesday, 12 February 2019 at 07:46:24 UTC, Radu wrote:
 On Monday, 11 February 2019 at 23:52:50 UTC, Stefan Koch wrote:
 On Saturday, 9 February 2019 at 15:38:55 UTC, kinke wrote:
 [...]

 IIRC __chkstk is a msvcrt call to dynamically grow the stack.
 There might be a hidden dependency introduced by llvm?

 A good explanation on this:
 https://metricpanda.com/rival-fortress-update-45-dealing-with-__chkstk-__chkstk_ms-when-cross-compiling-for-windows

I wanted to spare you the details, but that's the workaround 
which at least works without LTO: 
https://github.com/ldc-developers/druntime/blob/ldc/src/rt/msvc.c#L93-L99

Feb 12 2019

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digitalmars.D.ldc - fabs not being inlined?