On Tue, Aug 9, 2016 at 4:51 AM, Kugan Vivekanandarajah <kugan.vivekanandara...@linaro.org> wrote: > Hi Richard, > > Thanks for the review. > > On 29 April 2016 at 20:47, Richard Biener <richard.guent...@gmail.com> wrote: >> On Sun, Apr 17, 2016 at 1:14 AM, kugan >> <kugan.vivekanandara...@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. > > > Please find a modified version which checks for two-valued variable > and uses this to optimize. In the attached test case (in function > bar), we end up doing the conversion twice. > > Bootstrapped and regression tested on x86_64-linux-gnu without no new > regressions. Is this OK for trunk?
+/* Return true if VAR is a two-valued variable. Set MIN and MAX when it is + true. Return false otherwise. */ + +static bool +two_valued_val_range_p (tree var, tree *min, tree *max) +{ I'd use A and B, not MIN/MAX given it's two values, not necessarily a two-valued range (for example for ~[1, UINT_MAX-1] which you don't handle). In theory VRP might get a more sophisticated range representation to also allow a range consisting of just 3 and 7 for example. + tree tmp + = int_const_binop (PLUS_EXPR, + vr->min, + build_int_cst_type (TREE_TYPE (var), 1)); + if (0 != compare_values (tmp, vr->max)) + return false; I think simply if (wi::sub (vr->max, vr->min) == 1) might work as well and avoid building a tree node. + /* Convert: + LHS = CST BINOP VAR + where VAR is two-valued. + + To: + LHS = VAR == VAL1 ? (CST BINOP VAL1) : (CST BINOP VAL2) */ + + if (TREE_CODE_CLASS (rhs_code) == tcc_binary + && TREE_CODE (rhs1) == INTEGER_CST + && TREE_CODE (rhs2) == SSA_NAME Note that for all commutative tcc_binary operators the constant will be on the other operand. I think you need to handle the constant appearing in both places (and for division for example watch out for a zero divisor). + && has_single_use (rhs2) + && two_valued_val_range_p (rhs2, &min, &max)) + + { + tree cond = build2 (EQ_EXPR, TREE_TYPE (rhs2), rhs2, min); + tree new_rhs1 = int_const_binop (rhs_code, rhs1, min); + tree new_rhs2 = int_const_binop (rhs_code, rhs1, max); too many spaces after '='. + + if (new_rhs1 && new_rhs2) You didn't address my point about profitability - you test for a single use but not for the kind of use. Please instead use && single_imm_use (rhs2, &use_p, &use_stmt) && gimple_code (use_stmt) == GIMPLE_COND The testcase won't work on targets with small integers thus please require int32plus. With the existing scan-dumps it's not obvious what transform it is testing for - please add a comment before the dump scan reflecting the desired transform. Maybe also scan "optimized" instead to also verify that followup transforms trigger. Thanks, Richard. > Thanks, > Kugan > > gcc/testsuite/ChangeLog: > > 2016-08-09 Kugan Vivekanandarajah <kug...@linaro.org> > > PR tree-optimization/61839 > * gcc.dg/tree-ssa/pr61839.c: New test. > > gcc/ChangeLog: > > 2016-08-09 Kugan Vivekanandarajah <kug...@linaro.org> > > PR tree-optimization/61839 > * tree-vrp.c (two_valued_val_range_p): New. > (simplify_stmt_using_ranges): Convert CST BINOP VAR where VAR is > two-valued to VAR == VAL1 ? (CST BINOP VAL1) : (CST BINOP VAL2).