Fold bswap32(x) != 0 to x != 0 (and related transforms)

This patch to match.pd implements several closely related folding
simplifications at the tree-level, that make use of the property
that bit permutation functions, rotate and bswap have inverses.

[1]	bswap(X) eq/ne C, for constant C, simplifies to X eq/ne C'
	where C'=bswap(C), generalizing the transform in the subject.
[2]	bswap(X) eq/ne bswap(Y) simplifies to X eq/ne Y.
[3]	lrotate(X,C1) eq/ne C2 simplifies to X eq/ne C3, where
	C3 = rrotate(C2,C1), i.e. apply the inverse rotation to C2.
[4]	Likewise, rrotate(X,C1) eq/ne C2 simplifies to X eq/ne C3,
	where C3 = lrotate(C2,C1).
[5]	rotate(X,Z) eq/ne rotate(Y,Z) simplifies to X eq/ne Y, when
	the bit-count Z (the same on both sides) has no side-effects.
[6]	rotate(X,Y) eq/ne 0 simplifies to X eq/ne 0 if Y has no
	side-effects.
[7]	Likewise, rotate(X,Y) eq/ne -1 simplifies to X eq/ne -1,
	if Y has no side-effects.

2010-07-26  Roger Sayle  <roger@nextmovesoftware.com>
	    Marc Glisse  <marc.glisse@inria.fr>

gcc/ChangeLog
	* match.pd (rotate): Simplify equality/inequality of rotations.
	(bswap): Simplify equality/inequality tests of byte swapping.

gcc/testsuite/ChangeLog
	* gcc.dg/fold-eqrotate-1.c: New test case.
	* gcc.dg/fold-eqbswap-1.c: New test case.

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