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The following testcase is miscompiled, because niter analysis miscomputes the number of iterations to 0. The problem is that niter analysis uses mpz_t (wonder why, wouldn't widest_int do the same job?) and when wi::to_mpz is called e.g. on the TYPE_MAX_VALUE of __uint128_t, it initializes the mpz_t result with wrong value. wi::to_mpz has code to handle negative wide_ints in signed types by inverting all bits, importing to mpz and complementing it, which is fine, but doesn't handle correctly the case when the wide_int's len (times HOST_BITS_PER_WIDE_INT) is smaller than precision when wi::neg_p. E.g. the 0xffffffffffffffffffffffffffffffff TYPE_MAX_VALUE is represented in wide_int as 0xffffffffffffffff len 1, and wi::to_mpz would create 0xffffffffffffffff mpz_t value from that. This patch handles it by adding the needed -1 host wide int words (and has also code to deal with precision that aren't multiple of HOST_BITS_PER_WIDE_INT). 2020-12-31 Jakub Jelinek <jakub@redhat.com> PR tree-optimization/98474 * wide-int.cc (wi::to_mpz): If wide_int has MSB set, but type is unsigned and excess negative, append set bits after len until precision. * gcc.c-torture/execute/pr98474.c: New test.
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