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As observed by Jakub in comment #2 of PR 98865, the expression -(a>>63) is optimized in GENERIC but not in GIMPLE. Investigating further it turns out that this is one of a few transformations performed by fold_negate_expr in fold-const.c that aren't yet performed by match.pd. This patch moves/duplicates them there, and should be relatively safe as these transformations are already performed by the compiler, but just in different passes. This revised patch adds a Boolean simplify argument to tree-ssa-sccvn.c's vn_nary_build_or_lookup_1 to control whether simplification should be performed before value numbering, updating the callers, but then avoiding simplification when constructing/value-numbering NEGATE_EXPR. This avoids the regression of gcc.dg/tree-ssa/ssa-free-88.c, and enables the new test case(s) to pass. 2021-09-22 Roger Sayle <roger@nextmovesoftware.com> Richard Biener <rguenther@suse.de> gcc/ChangeLog * match.pd (negation simplifications): Implement some negation folding transformations from fold-const.c's fold_negate_expr. * tree-ssa-sccvn.c (vn_nary_build_or_lookup_1): Add a SIMPLIFY argument, to control whether the op should be simplified prior to looking up/assigning a value number. (vn_nary_build_or_lookup): Update call to vn_nary_build_or_lookup_1. (vn_nary_simplify): Likewise. (visit_nary_op): Likewise, but when constructing a NEGATE_EXPR now call vn_nary_build_or_lookup_1 disabling simplification. gcc/testsuite/ChangeLog * gcc.dg/fold-negate-1.c: New test case. |
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