https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79981
--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> --- (In reply to Dominik Vogt from comment #3) > (In reply to Richard Biener from comment #2) > > of course needs to be conditional on oldlhs being bool and lhs being > > integral. > > Like so? > > -- > diff --git a/gcc/gimple-fold.c b/gcc/gimple-fold.c > index 9fd45d1..e5e448e 100644 > --- a/gcc/gimple-fold.c > +++ b/gcc/gimple-fold.c > @@ -3581,7 +3581,12 @@ fold_builtin_atomic_compare_exchange > (gimple_stmt_iterator *gsi) > } > else > gsi_insert_after (gsi, g, GSI_NEW_STMT); > - g = gimple_build_assign (oldlhs, NOP_EXPR, gimple_assign_lhs (g)); > + if (TREE_CODE (TREE_TYPE (oldlhs)) == BOOLEAN_TYPE > + && INTEGRAL_TYPE_P (itype)) > + g = gimple_build_assign (oldlhs, NE_EXPR, gimple_assign_lhs (g), > + build_zero_cst (TREE_TYPE (gimple_assign_lhs > (g)))); > + else > + g = gimple_build_assign (oldlhs, NOP_EXPR, gimple_assign_lhs (g)); > gsi_insert_after (gsi, g, GSI_NEW_STMT); > } > g = gimple_build_assign (make_ssa_name (itype), REALPART_EXPR, That looks like a pessimization instead of optimization, perhaps optimizers then do a better job at that, but maybe in other cases don't. Wouldn't it be better to look after building the NOP_EXPR at the immediate uses of oldlhs and if any of them is oldlhs != 0 or oldlhs == 0 comparison, forward propagate there immediately the rhs1 of the nop and adjust the other operand?
