Patch to allow (not enforce) -flto compilation on GCC \ VOGONS

Patch to allow (not enforce) -flto compilation on GCC

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First post, by TeaRex

Posted on 2012-10-13, 19:00

TeaRex Offline

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The following small patch makes it possible to compile DOSBox under GCC with link-time optimization without hitting compilation errors regarding duplicate labels, caused by including the FPU assembly code several times (for the several cores). It does that by using GCC's local label feature.

Of its own it doesn't enable -flto though, you have to do that yourself. If -flto is not enabled, it changes nothing. If it is enabled though, your DOSBox becomes noticeably faster, at least it does on my Core2Quad Linux system.

1--- src/fpu/fpu_instructions_x86.h	(revision 3798)
2+++ src/fpu/fpu_instructions_x86.h	(working copy)
3@@ -660,9 +660,9 @@
4 			"fstpt		(%2, %%eax)		\n"	\
5 			"movw		%0, %%ax		\n"	\
6 			"sahf						\n"	\
7-			"jp			argument_too_large1		\n"	\
8+			"jp			1f		\n"	\
9 			"fstpt		(%2, %1)		\n"	\
10-			"argument_too_large1:		"	\
11+			"1:		"	\
12 			:	"=m" (new_sw)				\
13 			:	"r" (TOP), "r" (fpu.p_regs)	\
14 			:	"eax", "cc", "memory"		\
15@@ -686,9 +686,9 @@
16 			"fstpt		(%2, %%eax)		\n"	\
17 			"movw		%0, %%ax		\n"	\
18 			"sahf						\n"	\
19-			"jp			argument_too_large2		\n"	\
20+			"jp			1f		\n"	\
21 			"fstpt		(%2, %1)		\n"	\
22-			"argument_too_large2:		"	\
23+			"1:		"	\
24 			:	"=m" (new_sw)				\
25 			:	"r" (TOP), "r" (fpu.p_regs)	\
26 			:	"eax", "cc", "memory"		\

[/code]

tearex

Reply 1 of 7, by Qbix

Posted on 2012-10-13, 19:24

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are you sure that replacing it both times with 1: is correct ?
As that would give me the same label in both functions.

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Reply 2 of 7, by gulikoza

Posted on 2012-10-13, 20:09

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It's a local label according to this. The f suffix refers to the next (forward) label. 😀

http://www.si-gamer.net/gulikoza

Reply 3 of 7, by TeaRex

Posted on 2012-10-14, 09:37

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Yes it's fine. "jmp 1f" just gets translated to "jump to the NEXT place where there's a label called 1". So you can have it as often as you want.

tearex

Reply 4 of 7, by Serious Callers Only

Posted on 2012-10-29, 17:36

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Is this going to get committed? It would be nice to have for my mt32 ppa build (if i can figure out if it can build separately and still flto optimization, since the mt32emu lib uses cmake).

(especially since ppa's enforce 64 bits installs for 64 bit OS, so dosbox is generally a bit slower for the dynarec core)

Reply 5 of 7, by Qbix

Posted on 2012-10-29, 18:07

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maybe, wondering why the original code doesn't work.
Is there some limit to the length of a label?

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Reply 6 of 7, by Serious Callers Only

Posted on 2012-10-29, 18:43

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No clue myself, haven't tried it yet 😉

Reply 7 of 7, by Qbix

Posted on 2012-10-30, 09:31

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Thanks to some articles provided by rcblanke, I understand the issue a bit better. The patch makes sense.

Commited as revision 3799

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