The following reply was made to PR optimization/6162; it has been noted by GNATS. From: Torbjorn Granlund To: Michael Matz Cc: Kevin Ryde , Nathanael Nerode , , , Subject: Re: optimization/6162: gcc 3.0.4: certain i386 asm reloader ice Date: 30 Oct 2002 23:55:08 +0100 Michael Matz writes: Wow. Indeed. Some of them even have such funny things like: __asm__ ("{a%I4|add%I4c} %1,%3,%4\n\t{ame|addme} %0,%2" \ : "=r" ((USItype) (sh)), \ "=&r" ((USItype) (sl)) \ : "%r" ((USItype) (ah)), \ "%r" ((USItype) (al)), \ "rI" ((USItype) (bl))); which obviously is broken, or Fixed in gmp's longlong.h: 2002-01-21 Torbjorn Granlund * longlong.h (32-bit powerpc add_ssaaaa): Remove spurious commutative declaration. __asm__ ("addu.co %1,%r4,%r5\n\taddu.ci %0,%r2,%r3" \ : "=r" ((USItype) (sh)), \ "=&r" ((USItype) (sl)) \ : "%rJ" ((USItype) (ah)), \ "rJ" ((USItype) (bh)), \ "%rJ" ((USItype) (al)), \ "rJ" ((USItype) (bl))) which is useless (they have the same constraints, so commutativity doesn't matter at all). Well, we put commutativity declarations where they apply for consistency. Some of them probably are just lucky, like: __asm__ ("add.f %1, %4, %5\n\tadc %0, %2, %3" \ : "=r" ((USItype) (sh)), \ "=&r" ((USItype) (sl)) \ : "%r" ((USItype) (ah)), \ "rIJ" ((USItype) (bh)), \ "%r" ((USItype) (al)), \ "rIJ" ((USItype) (bl))) If called with only variables, or constants already in the right operands, the swapping also doesn't take place. But if then also operand matching comes into play (like some asms in longlong and also your example) the chance of getting unlucky is even higher. Anyway given that longlong.h uses it I again looked into reload, and no, it simply can't handle correctly more than one pair which needs swapping. It keeps track of only one operand which is commutative (the 'commutative' variable), and it only tries each alternative twice at most (once normally and once with the last pair swapped). Therefore I think longlong.h is broken, but I wonder why this never popped up. In GCC, I doubt immediate values will be used for add_ssaaaa. In GMP immediates are used, but by conventions they are used for the 2nd operand. There are a couple of other packages that use longlong.h as well, but they don't use immediates. I suggest that we don't touch longlong.h, since it is not really a problem. Who knows, one day GCC might get this right. -- Torbjörn