Index: gcc/tree-ssa-copy.c =================================================================== --- gcc/tree-ssa-copy.c (revision 162957) +++ gcc/tree-ssa-copy.c (working copy) @@ -274,31 +274,23 @@ propagate_tree_value_into_stmt (gimple_s /*--------------------------------------------------------------------------- Copy propagation ---------------------------------------------------------------------------*/ -/* During propagation, we keep chains of variables that are copies of - one another. If variable X_i is a copy of X_j and X_j is a copy of - X_k, COPY_OF will contain: - - COPY_OF[i].VALUE = X_j - COPY_OF[j].VALUE = X_k - COPY_OF[k].VALUE = X_k - - After propagation, the copy-of value for each variable X_i is - converted into the final value by walking the copy-of chains and - updating COPY_OF[i].VALUE to be the last element of the chain. */ +/* Lattice for copy-propagation. The lattice is initialized to + UNDEFINED (value == NULL) for SSA names that can become a copy + of something or VARYING (value == self) if not (see get_copy_of_val + and stmt_may_generate_copy). Other values make the name a COPY + of that value. + + When visiting a statement or PHI node the lattice value for an + SSA name can transition from UNDEFINED to COPY to VARYING. */ struct prop_value_d { /* Copy-of value. */ tree value; }; - typedef struct prop_value_d prop_value_t; static prop_value_t *copy_of; -/* Used in set_copy_of_val to determine if the last link of a copy-of - chain has changed. */ -static tree *cached_last_copy_of; - /* Return true if this statement may generate a useful copy. */ @@ -346,82 +338,38 @@ get_copy_of_val (tree var) return val; } +/* Return the variable VAR is a copy of or VAR if VAR isn't the result + of a copy. */ -/* Return last link in the copy-of chain for VAR. */ - -static tree -get_last_copy_of (tree var) +static inline tree +valueize_val (tree var) { - tree last; - int i; - - /* Traverse COPY_OF starting at VAR until we get to the last - link in the chain. Since it is possible to have cycles in PHI - nodes, the copy-of chain may also contain cycles. - - To avoid infinite loops and to avoid traversing lengthy copy-of - chains, we artificially limit the maximum number of chains we are - willing to traverse. - - The value 5 was taken from a compiler and runtime library - bootstrap and a mixture of C and C++ code from various sources. - More than 82% of all copy-of chains were shorter than 5 links. */ -#define LIMIT 5 - - last = var; - for (i = 0; i < LIMIT; i++) + if (TREE_CODE (var) == SSA_NAME) { - tree copy = copy_of[SSA_NAME_VERSION (last)].value; - if (copy == NULL_TREE || copy == last) - break; - last = copy; + tree val = get_copy_of_val (var)->value; + if (val) + return val; } - - /* If we have reached the limit, then we are either in a copy-of - cycle or the copy-of chain is too long. In this case, just - return VAR so that it is not considered a copy of anything. */ - return (i < LIMIT ? last : var); + return var; } - -/* Set FIRST to be the first variable in the copy-of chain for DEST. - If DEST's copy-of value or its copy-of chain has changed, return - true. - - MEM_REF is the memory reference where FIRST is stored. This is - used when DEST is a non-register and we are copy propagating loads - and stores. */ +/* Set VAL to be the copy of VAR. If that changed return true. */ static inline bool -set_copy_of_val (tree dest, tree first) +set_copy_of_val (tree var, tree val) { - unsigned int dest_ver = SSA_NAME_VERSION (dest); - tree old_first, old_last, new_last; + unsigned int ver = SSA_NAME_VERSION (var); + tree old; /* Set FIRST to be the first link in COPY_OF[DEST]. If that changed, return true. */ - old_first = copy_of[dest_ver].value; - copy_of[dest_ver].value = first; + old = copy_of[ver].value; + copy_of[ver].value = val; - if (old_first != first) + if (old != val) return true; - /* If FIRST and OLD_FIRST are the same, we need to check whether the - copy-of chain starting at FIRST ends in a different variable. If - the copy-of chain starting at FIRST ends up in a different - variable than the last cached value we had for DEST, then return - true because DEST is now a copy of a different variable. - - This test is necessary because even though the first link in the - copy-of chain may not have changed, if any of the variables in - the copy-of chain changed its final value, DEST will now be the - copy of a different variable, so we have to do another round of - propagation for everything that depends on DEST. */ - old_last = cached_last_copy_of[dest_ver]; - new_last = get_last_copy_of (dest); - cached_last_copy_of[dest_ver] = new_last; - - return (old_last != new_last); + return false; } @@ -431,50 +379,31 @@ static void dump_copy_of (FILE *file, tree var) { tree val; - sbitmap visited; print_generic_expr (file, var, dump_flags); - if (TREE_CODE (var) != SSA_NAME) return; - visited = sbitmap_alloc (num_ssa_names); - sbitmap_zero (visited); - SET_BIT (visited, SSA_NAME_VERSION (var)); - + val = copy_of[SSA_NAME_VERSION (var)].value; fprintf (file, " copy-of chain: "); - - val = var; - print_generic_expr (file, val, 0); + print_generic_expr (file, var, 0); fprintf (file, " "); - while (copy_of[SSA_NAME_VERSION (val)].value) + if (!val) + fprintf (file, "[UNDEFINED]"); + else if (val == var) + fprintf (file, "[NOT A COPY]"); + else { fprintf (file, "-> "); - val = copy_of[SSA_NAME_VERSION (val)].value; print_generic_expr (file, val, 0); fprintf (file, " "); - if (TEST_BIT (visited, SSA_NAME_VERSION (val))) - break; - SET_BIT (visited, SSA_NAME_VERSION (val)); + fprintf (file, "[COPY]"); } - - val = get_copy_of_val (var)->value; - if (val == NULL_TREE) - fprintf (file, "[UNDEFINED]"); - else if (val != var) - fprintf (file, "[COPY]"); - else - fprintf (file, "[NOT A COPY]"); - - sbitmap_free (visited); } /* Evaluate the RHS of STMT. If it produces a valid copy, set the LHS - value and store the LHS into *RESULT_P. If STMT generates more - than one name (i.e., STMT is an aliased store), it is enough to - store the first name in the VDEF list into *RESULT_P. After - all, the names generated will be VUSEd in the same statements. */ + value and store the LHS into *RESULT_P. */ static enum ssa_prop_result copy_prop_visit_assignment (gimple stmt, tree *result_p) @@ -485,7 +414,6 @@ copy_prop_visit_assignment (gimple stmt, lhs = gimple_assign_lhs (stmt); rhs = gimple_assign_rhs1 (stmt); - gcc_assert (gimple_assign_rhs_code (stmt) == SSA_NAME); rhs_val = get_copy_of_val (rhs); @@ -531,8 +459,8 @@ copy_prop_visit_cond_stmt (gimple stmt, are predicates involving two SSA_NAMEs. */ if (TREE_CODE (op0) == SSA_NAME && TREE_CODE (op1) == SSA_NAME) { - op0 = get_last_copy_of (op0); - op1 = get_last_copy_of (op1); + op0 = valueize_val (op0); + op1 = valueize_val (op1); /* See if we can determine the predicate's value. */ if (dump_file && (dump_flags & TDF_DETAILS)) @@ -642,7 +570,6 @@ copy_prop_visit_phi_node (gimple phi) { fprintf (dump_file, "\nVisiting PHI node: "); print_gimple_stmt (dump_file, phi, 0, dump_flags); - fprintf (dump_file, "\n\n"); } for (i = 0; i < gimple_phi_num_args (phi); i++) @@ -670,7 +597,8 @@ copy_prop_visit_phi_node (gimple phi) their loops and prevent coalescing opportunities. If the value was loop invariant, it will be hoisted by LICM and exposed for copy propagation. Not a problem for virtual - operands though. */ + operands though. + ??? The value will be always loop invariant. */ if (is_gimple_reg (lhs) && loop_depth_of_name (arg) > loop_depth_of_name (lhs)) { @@ -678,11 +606,6 @@ copy_prop_visit_phi_node (gimple phi) break; } - /* If the LHS appears in the argument list, ignore it. It is - irrelevant as a copy. */ - if (arg == lhs || get_last_copy_of (arg) == lhs) - continue; - if (dump_file && (dump_flags & TDF_DETAILS)) { fprintf (dump_file, "\tArgument #%d: ", i); @@ -692,30 +615,31 @@ copy_prop_visit_phi_node (gimple phi) arg_val = get_copy_of_val (arg); + /* If we didn't visit the definition of arg yet treat it as + UNDEFINED. This also handles PHI arguments that are the + same as lhs. We'll come here again. */ + if (!arg_val->value) + continue; + /* If the LHS didn't have a value yet, make it a copy of the - first argument we find. Notice that while we make the LHS be - a copy of the argument itself, we take the memory reference - from the argument's value so that we can compare it to the - memory reference of all the other arguments. */ + first argument we find. */ if (phi_val.value == NULL_TREE) { - phi_val.value = arg_val->value ? arg_val->value : arg; + phi_val.value = arg_val->value; continue; } /* If PHI_VAL and ARG don't have a common copy-of chain, then - this PHI node cannot be a copy operation. Also, if we are - copy propagating stores and these two arguments came from - different memory references, they cannot be considered - copies. */ - if (get_last_copy_of (phi_val.value) != get_last_copy_of (arg)) + this PHI node cannot be a copy operation. */ + if (phi_val.value != arg_val->value) { phi_val.value = lhs; break; } } - if (phi_val.value && may_propagate_copy (lhs, phi_val.value) + if (phi_val.value + && may_propagate_copy (lhs, phi_val.value) && set_copy_of_val (lhs, phi_val.value)) retval = (phi_val.value != lhs) ? SSA_PROP_INTERESTING : SSA_PROP_VARYING; else @@ -723,7 +647,7 @@ copy_prop_visit_phi_node (gimple phi) if (dump_file && (dump_flags & TDF_DETAILS)) { - fprintf (dump_file, "\nPHI node "); + fprintf (dump_file, "PHI node "); dump_copy_of (dump_file, lhs); fprintf (dump_file, "\nTelling the propagator to "); if (retval == SSA_PROP_INTERESTING) @@ -739,9 +663,7 @@ copy_prop_visit_phi_node (gimple phi) } -/* Initialize structures used for copy propagation. PHIS_ONLY is true - if we should only consider PHI nodes as generating copy propagation - opportunities. */ +/* Initialize structures used for copy propagation. */ static void init_copy_prop (void) @@ -750,8 +672,6 @@ init_copy_prop (void) copy_of = XCNEWVEC (prop_value_t, num_ssa_names); - cached_last_copy_of = XCNEWVEC (tree, num_ssa_names); - FOR_EACH_BB (bb) { gimple_stmt_iterator si; @@ -773,7 +693,8 @@ init_copy_prop (void) Otherwise, this may move loop variant variables outside of their loops and prevent coalescing opportunities. If the value was loop invariant, it will be hoisted by LICM and - exposed for copy propagation. */ + exposed for copy propagation. + ??? This doesn't make sense. */ if (stmt_ends_bb_p (stmt)) prop_set_simulate_again (stmt, true); else if (stmt_may_generate_copy (stmt) @@ -790,8 +711,6 @@ init_copy_prop (void) FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_ALL_DEFS) if (!prop_simulate_again_p (stmt)) set_copy_of_val (def, def); - else - cached_last_copy_of[SSA_NAME_VERSION (def)] = def; } /* In loop-closed SSA form do not copy-propagate through @@ -820,8 +739,6 @@ init_copy_prop (void) if (!prop_simulate_again_p (phi)) set_copy_of_val (def, def); - else - cached_last_copy_of[SSA_NAME_VERSION (def)] = def; } } } @@ -855,8 +772,6 @@ fini_copy_prop (void) || copy_of[i].value == var) continue; - copy_of[i].value = get_last_copy_of (var); - /* In theory the points-to solution of all members of the copy chain is their intersection. For now we do not bother to compute this but only make sure we do not lose points-to @@ -872,7 +787,6 @@ fini_copy_prop (void) substitute_and_fold (get_value, NULL, true); - free (cached_last_copy_of); free (copy_of); } @@ -908,81 +822,7 @@ fini_copy_prop (void) through edges marked executable by the propagation engine. So, when visiting statement #2 for the first time, we will only look at the first argument (a_24) and optimistically assume that its value - is the copy of a_24 (x_1). - - The problem with this approach is that it may fail to discover copy - relations in PHI cycles. Instead of propagating copy-of - values, we actually propagate copy-of chains. For instance: - - A_3 = B_1; - C_9 = A_3; - D_4 = C_9; - X_i = D_4; - - In this code fragment, COPY-OF (X_i) = { D_4, C_9, A_3, B_1 }. - Obviously, we are only really interested in the last value of the - chain, however the propagator needs to access the copy-of chain - when visiting PHI nodes. - - To represent the copy-of chain, we use the array COPY_CHAINS, which - holds the first link in the copy-of chain for every variable. - If variable X_i is a copy of X_j, which in turn is a copy of X_k, - the array will contain: - - COPY_CHAINS[i] = X_j - COPY_CHAINS[j] = X_k - COPY_CHAINS[k] = X_k - - Keeping copy-of chains instead of copy-of values directly becomes - important when visiting PHI nodes. Suppose that we had the - following PHI cycle, such that x_52 is already considered a copy of - x_53: - - 1 x_54 = PHI - 2 x_53 = PHI - - Visit #1: x_54 is copy-of x_53 (because x_52 is copy-of x_53) - Visit #2: x_53 is copy-of x_898 (because x_54 is a copy of x_53, - so it is considered irrelevant - as a copy). - Visit #1: x_54 is copy-of nothing (x_53 is a copy-of x_898 and - x_52 is a copy of x_53, so - they don't match) - Visit #2: x_53 is copy-of nothing - - This problem is avoided by keeping a chain of copies, instead of - the final copy-of value. Propagation will now only keep the first - element of a variable's copy-of chain. When visiting PHI nodes, - arguments are considered equal if their copy-of chains end in the - same variable. So, as long as their copy-of chains overlap, we - know that they will be a copy of the same variable, regardless of - which variable that may be). - - Propagation would then proceed as follows (the notation a -> b - means that a is a copy-of b): - - Visit #1: x_54 = PHI - x_53 -> x_53 - x_52 -> x_53 - Result: x_54 -> x_53. Value changed. Add SSA edges. - - Visit #1: x_53 = PHI - x_898 -> x_898 - x_54 -> x_53 - Result: x_53 -> x_898. Value changed. Add SSA edges. - - Visit #2: x_54 = PHI - x_53 -> x_898 - x_52 -> x_53 -> x_898 - Result: x_54 -> x_898. Value changed. Add SSA edges. - - Visit #2: x_53 = PHI - x_898 -> x_898 - x_54 -> x_898 - Result: x_53 -> x_898. Value didn't change. Stable state - - Once the propagator stabilizes, we end up with the desired result - x_53 and x_54 are both copies of x_898. */ + is the copy of a_24 (x_1). */ static unsigned int execute_copy_prop (void)