From 33d114f570b4a3583421c700396fd5945acebc28 Mon Sep 17 00:00:00 2001 From: Yang Yang Date: Tue, 30 Jun 2020 18:04:31 +0800 Subject: tree-optimization/95855 - Add checks to avoid spoiling if-conversion if Add some checks in pass_splits_paths, so that pass_split_paths can recognize the missed if-conversion opportunity and do not duplicate the corresponding block. 2020-06-30 Yang Yang gcc/ChangeLog: PR tree-optimization/95855 * gimple-ssa-split-paths.c (is_feasible_trace): Add extra checks to recognize a missed if-conversion opportunity when judging whether to duplicate a block. gcc/testsuite/ChangeLog PR tree-optimization/95855 * gcc.dg/tree-ssa/split-path-12.c: New testcase. --- gcc/gimple-ssa-split-paths.c | 39 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 39 insertions(+) (limited to 'gcc/gimple-ssa-split-paths.c') diff --git a/gcc/gimple-ssa-split-paths.c b/gcc/gimple-ssa-split-paths.c index b3efd43..9c32da7 100644 --- a/gcc/gimple-ssa-split-paths.c +++ b/gcc/gimple-ssa-split-paths.c @@ -34,6 +34,7 @@ along with GCC; see the file COPYING3. If not see #include "gimple-ssa.h" #include "tree-phinodes.h" #include "ssa-iterators.h" +#include "fold-const.h" /* Given LATCH, the latch block in a loop, see if the shape of the path reaching LATCH is suitable for being split by duplication. @@ -254,6 +255,44 @@ is_feasible_trace (basic_block bb) } } + /* Canonicalize the form. */ + if (single_pred_p (pred1) && single_pred (pred1) == pred2 + && num_stmts_in_pred1 == 0) + std::swap (pred1, pred2); + + /* This is meant to catch another kind of cases that are likely opportunities + for if-conversion. After canonicalizing, PRED2 must be an empty block and + PRED1 must be the only predecessor of PRED2. Moreover, PRED1 is supposed + to end with a cond_stmt which has the same args with the PHI in BB. */ + if (single_pred_p (pred2) && single_pred (pred2) == pred1 + && num_stmts_in_pred2 == 0) + { + gimple *cond_stmt = last_stmt (pred1); + if (cond_stmt && gimple_code (cond_stmt) == GIMPLE_COND) + { + tree lhs = gimple_cond_lhs (cond_stmt); + tree rhs = gimple_cond_rhs (cond_stmt); + + gimple_stmt_iterator gsi; + for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi)) + { + gimple *phi = gsi_stmt (gsi); + if ((operand_equal_p (gimple_phi_arg_def (phi, 0), lhs) + && operand_equal_p (gimple_phi_arg_def (phi, 1), rhs)) + || (operand_equal_p (gimple_phi_arg_def (phi, 0), rhs) + && (operand_equal_p (gimple_phi_arg_def (phi, 1), lhs)))) + { + if (dump_file && (dump_flags & TDF_DETAILS)) + fprintf (dump_file, + "Block %d appears to be optimized to a join " + "point for if-convertable half-diamond.\n", + bb->index); + return false; + } + } + } + } + /* If the joiner has no PHIs with useful uses there is zero chance of CSE/DCE/jump-threading possibilities exposed by duplicating it. */ bool found_useful_phi = false; -- cgit v1.1