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This patch implements several constant folding optimizations for __builtin_parity and friends. We canonicalize popcount(x)&1 as parity(x) in gimple, and potentially convert back again when we expand to RTL. parity(~x) is simplified to parity(x), which is true for all integer modes with an even number of bits. But probably most usefully, parity(x)^parity(y) can be simplified to a parity(x^y), requiring only a single libcall or popcount. This patch optimizes popcount and parity of an argument known to have at most a single bit set, to be that single bit. Hence, popcount(x&8) is simplified to (x>>3)&1. This generalizes the existing optimization of popcount(x&1) being simplified to x&1, which is cleaned up with this patch. 2020-07-28 Roger Sayle <roger@nextmovesoftware.com> Richard Biener <rguenther@suse.de> gcc/ChangeLog * match.pd (popcount(x)&1 -> parity(x)): New simplification. (parity(~x) -> parity(x)): New simplification. (parity(x)^parity(y) -> parity(x^y)): New simplification. (parity(x&1) -> x&1): New simplification. (popcount(x) -> x>>C): New simplification. gcc/testsuite/ChangeLog * gcc.dg/fold-popcount-5.c: New test. * gcc.dg/fold-parity-1.c: Likewise. * gcc.dg/fold-parity-2.c: Likewise. * gcc.dg/fold-parity-3.c: Likewise. * gcc.dg/fold-parity-4.c: Likewise. * gcc.dg/fold-parity-5.c: Likewise.
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