| Message ID | 5712C739.4080101@linaro.org |
|---|---|
| State | New |
| Headers | show |
On Sun, Apr 17, 2016 at 1:14 AM, kugan <kugan.vivekanandarajah@linaro.org> wrote: > As explained in PR61839, > > Following difference results in extra instructions: > - c = b != 0 ? 486097858 : 972195717; > + c = a + 972195718 >> (b != 0); > > As suggested in PR, attached patch converts CST BINOP COND_EXPR to COND_EXPR > ? (CST BINOP 1) : (CST BINOP 0). > > Bootstrapped and regression tested for x86-64-linux-gnu with no new > regression. Is this OK for statege-1. You are missing a testcase. I think the transform can be generalized to any two-value value-range by instead of lhs = cond_res ? (cst binop 1) : (cst binop 0) emitting lhs = tmp == val1 ? (cst binop val1) : (cst binop val2); In the PR I asked the transform to be only carried out if cond_res and tmp have a single use (and thus they'd eventually vanish). I'm not sure if a general two-value "constant" propagation is profitable which is why I was originally asking for the pattern to only apply if the resulting value is used in a comparison which we could then in turn simplify by substituting COND_RES (or ! COND_RES) for it. For the general two-value case we'd substitute it with tmp [=!]= val[12] dependent on which constant is cheaper to test for. So I think this needs some exploring work on which way to go and which transform is profitable in the end. I think the general two-value case feeding a condition will be always profitable. Thanks, Richard. > Thanks, > Kugan > > gcc/ChangeLog: > > 2016-04-17 Kugan Vivekanandarajah <kuganv@linaro.org> > Add PR tree-optimization/61839 > * tree-vrp.c (simplify_stmt_using_ranges): Convert CST BINOP > COND_EXPR to > COND_EXPR ? (CST BINOP 1) : (CST BINOP 0) when possible.
diff --git a/gcc/tree-vrp.c b/gcc/tree-vrp.c index bbdf9ce..caf7a2a 100644 --- a/gcc/tree-vrp.c +++ b/gcc/tree-vrp.c @@ -9902,6 +9902,49 @@ simplify_stmt_using_ranges (gimple_stmt_iterator *gsi) { enum tree_code rhs_code = gimple_assign_rhs_code (stmt); tree rhs1 = gimple_assign_rhs1 (stmt); + tree rhs2 = gimple_assign_rhs2 (stmt); + tree var; + + /* Convert: + COND_RES = X COMPARE Y + TMP = (CAST) COND_RES + LHS = CST BINOP TMP + + To: + LHS = COND_RES ? (CST BINOP 1) : (CST BINOP 0) */ + + if (TREE_CODE_CLASS (rhs_code) == tcc_binary + && TREE_CODE (rhs1) == INTEGER_CST + && TREE_CODE (rhs2) == SSA_NAME + && is_gimple_assign (SSA_NAME_DEF_STMT (rhs2)) + && gimple_assign_rhs_code (SSA_NAME_DEF_STMT (rhs2)) == NOP_EXPR + && (var = gimple_assign_rhs1 (SSA_NAME_DEF_STMT (rhs2))) + && TREE_CODE (var) == SSA_NAME + && is_gimple_assign (SSA_NAME_DEF_STMT (var)) + && TREE_CODE_CLASS (gimple_assign_rhs_code (SSA_NAME_DEF_STMT (var))) + == tcc_comparison) + + { + value_range *vr = get_value_range (var); + if (range_int_cst_p (vr) + && integer_zerop (vr->min) + && integer_onep (vr->max)) + { + + tree new_rhs1 = int_const_binop (rhs_code, rhs1, vr->max); + tree new_rhs2 = int_const_binop (rhs_code, rhs1, vr->min); + + if (new_rhs1 && new_rhs2) + { + gimple_assign_set_rhs_with_ops (gsi, + COND_EXPR, var, + new_rhs1, + new_rhs2); + update_stmt (gsi_stmt (*gsi)); + return true; + } + } + } switch (rhs_code) {