[Scummvm-cvs-logs] SF.net SVN: scummvm:[52480] scummvm/trunk/common/endian.h

Bluddy at users.sourceforge.net Bluddy at users.sourceforge.net
Wed Sep 1 14:41:16 CEST 2010


Revision: 52480
          http://scummvm.svn.sourceforge.net/scummvm/?rev=52480&view=rev
Author:   Bluddy
Date:     2010-09-01 12:41:16 +0000 (Wed, 01 Sep 2010)

Log Message:
-----------
COMMON: changed read/write endian function to use __may_alias__ attribute

This is a better solution for the gcc aliasing problem that happens when aliasing a struct onto something else. What happens is that the compiler assumes no aliasing can happen when -O2 and -O3 are activated, and a call to READ_UINT32() followed by WRITE_UINT32() and another READ_UINT32() will be optimized to return the original read value instead of re-reading.

Modified Paths:
--------------
    scummvm/trunk/common/endian.h

Modified: scummvm/trunk/common/endian.h
===================================================================
--- scummvm/trunk/common/endian.h	2010-09-01 09:48:00 UTC (rev 52479)
+++ scummvm/trunk/common/endian.h	2010-09-01 12:41:16 UTC (rev 52480)
@@ -189,22 +189,22 @@
 #elif defined(__GNUC__) && (__GNUC__ >= 4)
 
 	FORCEINLINE uint16 READ_UINT16(const void *ptr) {
-		struct Unaligned16 { uint16 val; } __attribute__ ((__packed__));
+		struct Unaligned16 { uint16 val; } __attribute__ ((__packed__, __may_alias__));
 		return ((const Unaligned16 *)ptr)->val;
 	}
 
 	FORCEINLINE uint32 READ_UINT32(const void *ptr) {
-		struct Unaligned32 { uint32 val; } __attribute__ ((__packed__));
+		struct Unaligned32 { uint32 val; } __attribute__ ((__packed__, __may_alias__));
 		return ((const Unaligned32 *)ptr)->val;
 	}
 
 	FORCEINLINE void WRITE_UINT16(void *ptr, uint16 value) {
-		struct Unaligned16 { uint16 val; } __attribute__ ((__packed__));
+		struct Unaligned16 { uint16 val; } __attribute__ ((__packed__, __may_alias__));
 		((Unaligned16 *)ptr)->val = value;
 	}
 
 	FORCEINLINE void WRITE_UINT32(void *ptr, uint32 value) {
-		struct Unaligned32 { uint32 val; } __attribute__ ((__packed__));
+		struct Unaligned32 { uint32 val; } __attribute__ ((__packed__, __may_alias__));
 		((Unaligned32 *)ptr)->val = value;
 	}
 


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