From: Jakub Jelinek Date: Wed, 4 Nov 2020 10:55:29 +0000 (+0100) Subject: phiopt: Optimize x ? 1024 : 0 to (int) x << 10 [PR97690] X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=3e190757fa332d327bee27495f37beb01155cfab;p=gcc.git phiopt: Optimize x ? 1024 : 0 to (int) x << 10 [PR97690] The following patch generalizes the x ? 1 : 0 -> (int) x optimization to handle also left shifts by constant. During x86_64-linux and i686-linux bootstraps + regtests it triggered in 1514 unique non-LTO -m64 cases (sort -u on log mentioning filename, function name and shift count) and 1866 -m32 cases. Unfortunately, the patch regresses (before the tests have been adjusted): +FAIL: gcc.dg/tree-ssa/ssa-ccp-11.c scan-tree-dump-times optimized "if " 0 +FAIL: gcc.dg/vect/bb-slp-pattern-2.c -flto -ffat-lto-objects scan-tree-dump-times slp1 "optimized: basic block" 1 +FAIL: gcc.dg/vect/bb-slp-pattern-2.c scan-tree-dump-times slp1 "optimized: basic block" 1 and in both cases it actually results in worse code. > > We'd need some optimization that would go through all PHI edges and > > compute if some use of the phi results don't actually compute a constant > > across all the PHI edges - 1 & 0 and 0 & 1 is always 0. > PRE should do this, IMHO only optimizing it at -O2 is fine. > > Similarly, in the slp vectorization test there is: > > a[0] = b[0] ? 1 : 7; > note this, carefully avoiding the already "optimized" b[0] ? 1 : 0 ... > So the option is to put : 7 in the 2, 4 an 8 case as well. The testcase > wasn't added for any real-world case but is artificial I guess for > COND_EXPR handling of invariants. > But yeah, for things like SLP it means we eventually have to > implement reverse transforms for all of this to make the lanes > matching. But that's true anyway for things like x + 1 vs. x + 0 > or x / 3 vs. x / 2 or other simplifications we do. 2020-11-04 Jakub Jelinek PR tree-optimization/97690 * tree-ssa-phiopt.c (conditional_replacement): Also optimize cond ? pow2p_cst : 0 as ((type) cond) << cst. * gcc.dg/tree-ssa/phi-opt-22.c: New test. * gcc.dg/tree-ssa/ssa-ccp-11.c: Use -O2 instead of -O1. * gcc.dg/vect/bb-slp-pattern-2.c (foo): Use ? 2 : 7, ? 4 : 7 and ? 8 : 7 instead of ? 2 : 0, ? 4 : 0, ? 8 : 0. --- diff --git a/gcc/testsuite/gcc.dg/tree-ssa/phi-opt-22.c b/gcc/testsuite/gcc.dg/tree-ssa/phi-opt-22.c new file mode 100644 index 00000000000..fd37066662b --- /dev/null +++ b/gcc/testsuite/gcc.dg/tree-ssa/phi-opt-22.c @@ -0,0 +1,11 @@ +/* PR tree-optimization/97690 */ +/* { dg-do compile } */ +/* { dg-options "-O2 -fdump-tree-phiopt2" } */ + +int foo (_Bool d) { return d ? 2 : 0; } +int bar (_Bool d) { return d ? 1 : 0; } +int baz (_Bool d) { return d ? -__INT_MAX__ - 1 : 0; } +int qux (_Bool d) { return d ? 1024 : 0; } + +/* { dg-final { scan-tree-dump-not "if" "phiopt2" } } */ +/* { dg-final { scan-tree-dump-times " << " 3 "phiopt2" } } */ diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-ccp-11.c b/gcc/testsuite/gcc.dg/tree-ssa/ssa-ccp-11.c index 36b8e7fc8fd..d70ea5a0189 100644 --- a/gcc/testsuite/gcc.dg/tree-ssa/ssa-ccp-11.c +++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-ccp-11.c @@ -1,5 +1,5 @@ /* { dg-do compile } */ -/* { dg-options "-O1 -fdump-tree-optimized" } */ +/* { dg-options "-O2 -fdump-tree-optimized" } */ /* Test for CPROP across a DAG. */ diff --git a/gcc/testsuite/gcc.dg/vect/bb-slp-pattern-2.c b/gcc/testsuite/gcc.dg/vect/bb-slp-pattern-2.c index f6b99ea69a4..c50560b5369 100644 --- a/gcc/testsuite/gcc.dg/vect/bb-slp-pattern-2.c +++ b/gcc/testsuite/gcc.dg/vect/bb-slp-pattern-2.c @@ -13,13 +13,13 @@ foo (short * __restrict__ a, int * __restrict__ b, int stride) for (i = 0; i < N/stride; i++, a += stride, b += stride) { a[0] = b[0] ? 1 : 7; - a[1] = b[1] ? 2 : 0; + a[1] = b[1] ? 2 : 7; a[2] = b[2] ? 3 : 0; - a[3] = b[3] ? 4 : 0; + a[3] = b[3] ? 4 : 7; a[4] = b[4] ? 5 : 0; a[5] = b[5] ? 6 : 0; a[6] = b[6] ? 7 : 0; - a[7] = b[7] ? 8 : 0; + a[7] = b[7] ? 8 : 7; } } diff --git a/gcc/tree-ssa-phiopt.c b/gcc/tree-ssa-phiopt.c index aa6bb88848b..e2758b2bd64 100644 --- a/gcc/tree-ssa-phiopt.c +++ b/gcc/tree-ssa-phiopt.c @@ -752,7 +752,9 @@ conditional_replacement (basic_block cond_bb, basic_block middle_bb, gimple_stmt_iterator gsi; edge true_edge, false_edge; tree new_var, new_var2; - bool neg; + bool neg = false; + int shift = 0; + tree nonzero_arg; /* FIXME: Gimplification of complex type is too hard for now. */ /* We aren't prepared to handle vectors either (and it is a question @@ -763,14 +765,22 @@ conditional_replacement (basic_block cond_bb, basic_block middle_bb, || POINTER_TYPE_P (TREE_TYPE (arg1)))) return false; - /* The PHI arguments have the constants 0 and 1, or 0 and -1, then - convert it to the conditional. */ - if ((integer_zerop (arg0) && integer_onep (arg1)) - || (integer_zerop (arg1) && integer_onep (arg0))) - neg = false; - else if ((integer_zerop (arg0) && integer_all_onesp (arg1)) - || (integer_zerop (arg1) && integer_all_onesp (arg0))) + /* The PHI arguments have the constants 0 and 1, or 0 and -1 or + 0 and (1 << cst), then convert it to the conditional. */ + if (integer_zerop (arg0)) + nonzero_arg = arg1; + else if (integer_zerop (arg1)) + nonzero_arg = arg0; + else + return false; + if (integer_all_onesp (nonzero_arg)) neg = true; + else if (integer_pow2p (nonzero_arg)) + { + shift = tree_log2 (nonzero_arg); + if (shift && POINTER_TYPE_P (TREE_TYPE (nonzero_arg))) + return false; + } else return false; @@ -782,12 +792,12 @@ conditional_replacement (basic_block cond_bb, basic_block middle_bb, falls through into BB. There is a single PHI node at the join point (BB) and its arguments - are constants (0, 1) or (0, -1). + are constants (0, 1) or (0, -1) or (0, (1 << shift)). So, given the condition COND, and the two PHI arguments, we can rewrite this PHI into non-branching code: - dest = (COND) or dest = COND' + dest = (COND) or dest = COND' or dest = (COND) << shift We use the condition as-is if the argument associated with the true edge has the value one or the argument associated with the @@ -822,6 +832,14 @@ conditional_replacement (basic_block cond_bb, basic_block middle_bb, cond = fold_build1_loc (gimple_location (stmt), NEGATE_EXPR, TREE_TYPE (cond), cond); } + else if (shift) + { + cond = fold_convert_loc (gimple_location (stmt), + TREE_TYPE (result), cond); + cond = fold_build2_loc (gimple_location (stmt), + LSHIFT_EXPR, TREE_TYPE (cond), cond, + build_int_cst (integer_type_node, shift)); + } /* Insert our new statements at the end of conditional block before the COND_STMT. */