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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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