On Wed, Oct 10, 2012 at 6:52 PM, Easwaran Raman <era...@google.com> wrote: > Hi, > In the expression reassociation pass, statements might get moved > downwards to ensure that dependences are not violated after > reassociation. This can increase the live range and, in a tight loop, > result in spills. This patch simply does a code motion of those > statements involved in reassociation and pushes them upwards in the BB > as far as possible without violating dependences. Bootstraps and no > tests regressions on a x86_64 machine running linux. Ok for trunk?
Can you post an example such as alder32 or loop in ffpmeg? The increased register pressure by re-association is a long standing issue. There was an earlier attempt to address it: http://gcc.1065356.n5.nabble.com/A-new-gimple-pass-LRS-live-range-shrinking-to-reduce-register-pressure-td495858.html > > > - Easwaran > > ----------- > 2012-10-10 Easwaran Raman <era...@google.com> > > * tree-ssa-reassoc.c (move_stmt_upwards): New function. > (rewrite_expr_tree): Record statements to be moved. > (reassociate_bb): Move statements affected by reassociation > as early as possible. > > Index: gcc/tree-ssa-reassoc.c > =================================================================== > --- gcc/tree-ssa-reassoc.c (revision 191879) > +++ gcc/tree-ssa-reassoc.c (working copy) > @@ -2250,13 +2250,51 @@ swap_ops_for_binary_stmt (VEC(operand_entry_t, hea > } > } > > +/* Move STMT up within its BB until it can not be moved any further. */ > + > +static void move_stmt_upwards (gimple stmt) static void move_stmt_upwards (...) > +{ > + gimple_stmt_iterator gsi, gsistmt; > + tree rhs1, rhs2; > + gimple rhs1def = NULL, rhs2def = NULL; New line needed. > + rhs1 = gimple_assign_rhs1 (stmt); > + rhs2 = gimple_assign_rhs2 (stmt); > + gcc_assert (rhs1); > + if (TREE_CODE (rhs1) == SSA_NAME) > + rhs1def = SSA_NAME_DEF_STMT (rhs1); > + else if (TREE_CODE (rhs1) != REAL_CST > + && TREE_CODE (rhs1) != INTEGER_CST) > + return; > + if (rhs2) > + { > + if (TREE_CODE (rhs2) == SSA_NAME) > + rhs2def = SSA_NAME_DEF_STMT (rhs2); > + else if (TREE_CODE (rhs1) != REAL_CST > + && TREE_CODE (rhs1) != INTEGER_CST) > + return; > + } It is possible to handle stmts with memory operation too, but that probably won't fit into the re-association pass. > + gsi = gsi_for_stmt (stmt); > + gsistmt = gsi; > + gsi_prev (&gsi); > + for (; !gsi_end_p (gsi); gsi_prev (&gsi)) > + { > + gimple curr_stmt = gsi_stmt (gsi); > + if (curr_stmt == rhs1def || curr_stmt == rhs2def) { > + gsi_move_after (&gsistmt, &gsi); > + return; > + } > + } > + > +} > + > /* Recursively rewrite our linearized statements so that the operators > match those in OPS[OPINDEX], putting the computation in rank > order. */ Document STMTS_TO_MOVE. > > static void > rewrite_expr_tree (gimple stmt, unsigned int opindex, > - VEC(operand_entry_t, heap) * ops, bool moved) > + VEC(operand_entry_t, heap) * ops, bool moved, > + VEC(gimple, heap) **stmts_to_move) > { > tree rhs1 = gimple_assign_rhs1 (stmt); > tree rhs2 = gimple_assign_rhs2 (stmt); > @@ -2299,6 +2337,7 @@ rewrite_expr_tree (gimple stmt, unsigned int opind > print_gimple_stmt (dump_file, stmt, 0, 0); > } > } > + VEC_safe_push (gimple, heap, *stmts_to_move, stmt); > return; > } > > @@ -2346,7 +2385,9 @@ rewrite_expr_tree (gimple stmt, unsigned int opind > } > /* Recurse on the LHS of the binary operator, which is guaranteed to > be the non-leaf side. */ > - rewrite_expr_tree (SSA_NAME_DEF_STMT (rhs1), opindex + 1, ops, moved); > + rewrite_expr_tree (SSA_NAME_DEF_STMT (rhs1), opindex + 1, ops, moved, > + stmts_to_move); > + VEC_safe_push (gimple, heap, *stmts_to_move, stmt); > } > > /* Find out how many cycles we need to compute statements chain. > @@ -3427,6 +3468,9 @@ reassociate_bb (basic_block bb) > { > gimple_stmt_iterator gsi; > basic_block son; > + VEC(gimple, heap) *stmts_to_move = NULL; > + gimple stmt; > + int i; > > for (gsi = gsi_last_bb (bb); !gsi_end_p (gsi); gsi_prev (&gsi)) > { > @@ -3542,7 +3586,7 @@ reassociate_bb (basic_block bb) > && VEC_length (operand_entry_t, ops) > 3) > rewrite_expr_tree_parallel (stmt, width, ops); > else > - rewrite_expr_tree (stmt, 0, ops, false); > + rewrite_expr_tree (stmt, 0, ops, false, &stmts_to_move); > > /* If we combined some repeated factors into a > __builtin_powi call, multiply that result by the > @@ -3560,6 +3604,7 @@ reassociate_bb (basic_block bb) > target_ssa); > gimple_set_location (mul_stmt, gimple_location (stmt)); > gsi_insert_after (&gsi, mul_stmt, GSI_NEW_STMT); > + VEC_safe_push (gimple, heap, stmts_to_move, mul_stmt); > } > } > > @@ -3567,6 +3612,11 @@ reassociate_bb (basic_block bb) > } > } > } > + > + FOR_EACH_VEC_ELT (gimple, stmts_to_move, i, stmt) > + move_stmt_upwards (stmt); > + VEC_free (gimple, heap, stmts_to_move); > + > for (son = first_dom_son (CDI_POST_DOMINATORS, bb); > son; > son = next_dom_son (CDI_POST_DOMINATORS, son))
