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As reported in the PR, tree-ssa-dom.cc uses real_zerop call to find if a floating point constant is zero and it shouldn't try to infer equivalences from comparison against it if signed zeros are honored. This doesn't work at all for decimal types, because real_zerop always returns false for them (one can have different representations of decimal zero beyond -0/+0), and it doesn't work for vector compares either, as real_zerop checks if all elements are zero, while we need to avoid infering equivalences from comparison against vector constants which have at least one zero element in it (if signed zeros are honored). Furthermore, as mentioned by Joseph, for decimal types many other values aren't singleton. So, this patch stops infering anything if element mode is decimal, and otherwise uses instead of real_zerop a new function, real_maybe_zerop, which will work even for decimal types and for complex or vector will return true if any element is or might be zero (so it returns true for anything but constants for now). 2022-12-23 Jakub Jelinek <jakub@redhat.com> PR tree-optimization/108068 * tree.h (real_maybe_zerop): Declare. * tree.cc (real_maybe_zerop): Define. * tree-ssa-dom.cc (record_edge_info): Use it instead of real_zerop or TREE_CODE (op1) == SSA_NAME || real_zerop. Always set can_infer_simple_equiv to false for decimal floating point types. * gcc.dg/dfp/pr108068.c: New test.
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