Re: Should we compile Guile with -fno-strict-aliasing?

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Re: Should we compile Guile with -fno-strict-aliasing?

From:	Ludovic Courtès
Subject:	Re: Should we compile Guile with -fno-strict-aliasing?
Date:	Fri, 27 Jan 2012 22:02:11 +0100
User-agent:	Gnus/5.110018 (No Gnus v0.18) Emacs/24.0.90 (gnu/linux)
Hi Mark,

Mark H Weaver <address@hidden> skribis:

> Perhaps we should simply add this compiler flag where its available, at
> least in the short term.  What do you think?

I’ve been thinking about that too, because on some platforms GCC emits
may-break-strict-aliasing-rules warnings, notably on x86_64-freebsd8.2
with GCC 4.2.1:

--8<---------------cut here---------------start------------->8---
vm.c: In function 'vm_reinstate_partial_continuation':
vm.c:281: warning: dereferencing type-punned pointer will break strict-aliasing 
rules
In file included from vm-engine.c:127,
                 from vm.c:467:
vm-i-system.c: In function 'vm_regular_engine':
vm-i-system.c:49: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:52: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:53: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:79: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:212: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:225: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:418: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:430: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:445: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:465: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:487: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:528: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:537: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:546: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:556: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:566: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:575: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:923: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:994: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1043: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1073: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1089: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1121: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1131: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1195: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1218: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1241: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1281: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1332: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1427: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1446: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1457: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1470: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1472: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1480: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1513: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1548: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1574: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1600: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1607: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1619: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1627: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1641: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1679: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1704: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1726: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1751: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1783: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
In file included from vm-engine.c:128,
                 from vm.c:467:
vm-i-scheme.c:192: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:203: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:599: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:624: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:626: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:629: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:692: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:809: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:859: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:861: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:863: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:865: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:867: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:869: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:871: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:873: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1016: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1016: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1018: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1018: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1020: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1020: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1022: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1022: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1024: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1024: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1026: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1026: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1028: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1028: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1030: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1030: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1119: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1121: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1123: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1125: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1128: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1134: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1139: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1141: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1143: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1145: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
In file included from vm-engine.c:129,
                 from vm.c:467:
vm-i-loader.c:65: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-loader.c:87: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-loader.c:99: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
In file included from vm-engine.c:127,
                 from vm.c:475:
vm-i-system.c: In function 'vm_debug_engine':
vm-i-system.c:49: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:52: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:53: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:79: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:212: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:225: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:418: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:430: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:445: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:465: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:487: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:528: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:537: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:546: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:556: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:566: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:575: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:923: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:994: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1043: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1073: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1089: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1121: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1131: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1195: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1218: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1241: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1281: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1325: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1332: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1367: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1427: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1446: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1457: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1470: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1472: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1480: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1513: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1548: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1574: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1600: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1607: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1619: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1627: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1641: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1679: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1704: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1726: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1751: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-system.c:1783: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
In file included from vm-engine.c:128,
                 from vm.c:475:
vm-i-scheme.c:192: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:203: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:599: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:624: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:626: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:629: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:692: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:809: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:859: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:861: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:863: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:865: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:867: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:869: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:871: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:873: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1016: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1016: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1018: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1018: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1020: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1020: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1022: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1022: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1024: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1024: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1026: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1026: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1028: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1028: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1030: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1030: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1119: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1121: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1123: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1125: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1128: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1134: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1139: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1141: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1143: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-scheme.c:1145: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
In file included from vm-engine.c:129,
                 from vm.c:475:
vm-i-loader.c:65: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-loader.c:87: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
vm-i-loader.c:99: warning: dereferencing type-punned pointer will break 
strict-aliasing rules
--8<---------------cut here---------------end--------------->8---

I’ve just tried on this platform and it seems to fix the threading
issues we were observing (though I won’t claim victory until Hydra
reproduces the success several times in a row ;-)).

It may well be that my recent COMPILER_BARRIER hack can just go away
with this.

I just committed the change.

Thank you!

Ludo’.
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Should we compile Guile with -fno-strict-aliasing?, Mark H Weaver, 2012/01/27
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  - Re: Should we compile Guile with -fno-strict-aliasing?, Ludovic Courtès, 2012/01/29
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