Re: Inlining with gcc 4.x.x (Linux) ?

So somebody has compiled GPC based on GCC 4.3?  This is good (latest I
had previously seen was 4.1).  Are patches available for any later
versions of GCC?

--------------------------|
John L. Ries              |
Salford Systems           |
Phone: (619)543-8880 x107 |
or     (435)867-8885      |
--------------------------|


On Tue, 10 Jan 2017, Peter wrote:

> I've built GPC 3.4.6 and 4.3.6 on Debian Stretch (64bit)
> Running benchmarks on a Perlin Noise routine I get
>
> 3.4.6    5.6 secs
> 4.3.6   11.0 secs   !!
>
> The difference seems to be mainly down to a failure of 4.3.6 to inline.
> Call functions themselves may not take much time but I believe the real
> problem is that without the subroutines inlined, the main Noise function
> is no longer a leaf function, and therefore under register pressure.
>
> ….....
>
>       a := Lerp (sx, u10, v10);
>       b := Lerp (sx, u11, v11);
>       d := Lerp (sy,  a,  b);
>
>     Noise3 := Lerp(sz, c, d);
> End;
>
>
> This code produces with 3.4.6
>
> 	{ Hard to know where it starts without line numbers ! }
> 	addsd	%xmm9, %xmm7
> 	addsd	%xmm3, %xmm2
> 	subsd	%xmm0, %xmm1
> 	subsd	%xmm7, %xmm2
> 	mulsd	%xmm14, %xmm1
> 	mulsd	%xmm14, %xmm2
> 	addsd	%xmm0, %xmm1
> 	addsd	%xmm7, %xmm2
> 	subsd	%xmm1, %xmm2
> 	mulsd	%xmm2, %xmm12
> 	movsd	%xmm12, %xmm0
> 	addsd	%xmm1, %xmm0
> 	ret
>
> which is pretty lean & mean.
>
>
> However, with 4.3.6 I get
>
> 	movsd	112(%rsp), %xmm2
> 	movsd	104(%rsp), %xmm1
> 	movsd	48(%rsp), %xmm0
> 	call	_p__M0_S5_Lerp
> 	movsd	128(%rsp), %xmm2
> 	movsd	%xmm0, 152(%rsp)
> 	movsd	120(%rsp), %xmm1
> 	movsd	48(%rsp), %xmm0
> 	call	_p__M0_S5_Lerp
> 	movsd	152(%rsp), %xmm1
> 	movapd	%xmm0, %xmm2
> 	movsd	56(%rsp), %xmm0
> 	call	_p__M0_S5_Lerp
> 	movsd	40(%rsp), %xmm1
> 	movapd	%xmm0, %xmm2
> 	movsd	64(%rsp), %xmm0
> 	call	_p__M0_S5_Lerp
> 	addq	$240, %rsp
> 	popq	%rbx
> 	popq	%rbp
> 	popq	%r12
> 	popq	%r13
> 	popq	%r14
> 	popq	%r15
> 	ret
>
>
> ( Stack spills tend to be expensive on [my] AMD processor as the level
> 0/1 cache isn't that fast.
>
>
> Maybe I have broken my build of 4.3.6   Can anyone else conform the
> status of inlining on linux x86 with 4.x.x compilers?  The simple
> example from the info file
>
> program InlineDemo;
>
>     function Max (x, y: Integer): Integer; attribute (inline);
>     begin
>         if x > y then
>            Max := x
>         else
>            Max := y
>     end;
>
>  begin
>         WriteLn (Max (42, 17), ' ', Max (-4, -2))
>  end.
>
>
> Also does not work for me with 4.3.6. It still produces a call instruction.
> 	call	_p__M0_S0_Max
>
>
> I recall also that inlining did not work with the official 4.1 Debian
> package. I was thinking of reporting this as a (Debian) bug a while
> back, but GPC was then removed from the archive, which made that moot.
>
>
> Going forward, I'm wondering which gcc version to base my builds on.
> 4.3.6 supports potentially a few more architectures,
> ARMel
> PowerPC
> SH4
>
> and supports the -m32 switch, but a 100% slowdown on the CPU intensive
> stuff I use the compiler for is too much a penalty for me.
>
> From further tinkering around, I notice that 3.4.6 often inlines even
> when not asked to do so, whereas 4.3.6 very rarely if ever inlines.
> Neither compiler seems to obey the inline attribute!
>
> Anyone any thoughts on this?
> Hoping of course that its an easy to fix typo type bug...
>
>
> Regards,
> Peter B
>
>
>
>
>
> _______________________________________________
> Gpc mailing list
> [email protected]
> https://www.g-n-u.de/mailman/listinfo/gpc

_______________________________________________
Gpc mailing list
[email protected]
https://www.g-n-u.de/mailman/listinfo/gpc