diff options
Diffstat (limited to 'gcc/tree-ssa-propagate.c')
| -rw-r--r-- | gcc/tree-ssa-propagate.c | 181 |
1 files changed, 5 insertions, 176 deletions
diff --git a/gcc/tree-ssa-propagate.c b/gcc/tree-ssa-propagate.c index 611f2b2..4c246e6 100644 --- a/gcc/tree-ssa-propagate.c +++ b/gcc/tree-ssa-propagate.c @@ -823,22 +823,6 @@ ssa_propagate (ssa_prop_visit_stmt_fn visit_stmt, } -/* Return the first VDEF operand for STMT. */ - -tree -first_vdef (gimple stmt) -{ - ssa_op_iter iter; - tree op; - - /* Simply return the first operand we arrive at. */ - FOR_EACH_SSA_TREE_OPERAND (op, stmt, iter, SSA_OP_VIRTUAL_DEFS) - return (op); - - gcc_unreachable (); -} - - /* Return true if STMT is of the form 'LHS = mem_ref', where 'mem_ref' is a non-volatile pointer dereference, a structure reference or a reference to a single _DECL. Ignore volatile memory references @@ -898,30 +882,6 @@ stmt_makes_single_store (gimple stmt) } -/* If STMT makes a single memory load and all the virtual use operands - have the same value in array VALUES, return it. Otherwise, return - NULL. */ - -prop_value_t * -get_value_loaded_by (gimple stmt, prop_value_t *values) -{ - ssa_op_iter i; - tree vuse; - prop_value_t *prev_val = NULL; - prop_value_t *val = NULL; - - FOR_EACH_SSA_TREE_OPERAND (vuse, stmt, i, SSA_OP_VIRTUAL_USES) - { - val = &values[SSA_NAME_VERSION (vuse)]; - if (prev_val && prev_val->value != val->value) - return NULL; - prev_val = val; - } - - return val; -} - - /* Propagation statistics. */ struct prop_stats_d { @@ -972,131 +932,6 @@ replace_uses_in (gimple stmt, prop_value_t *prop_value) } -/* Replace the VUSE references in statement STMT with the values - stored in PROP_VALUE. Return true if a reference was replaced. - - Replacing VUSE operands is slightly more complex than replacing - regular USEs. We are only interested in two types of replacements - here: - - 1- If the value to be replaced is a constant or an SSA name for a - GIMPLE register, then we are making a copy/constant propagation - from a memory store. For instance, - - # a_3 = VDEF <a_2> - a.b = x_1; - ... - # VUSE <a_3> - y_4 = a.b; - - This replacement is only possible iff STMT is an assignment - whose RHS is identical to the LHS of the statement that created - the VUSE(s) that we are replacing. Otherwise, we may do the - wrong replacement: - - # a_3 = VDEF <a_2> - # b_5 = VDEF <b_4> - *p = 10; - ... - # VUSE <b_5> - x_8 = b; - - Even though 'b_5' acquires the value '10' during propagation, - there is no way for the propagator to tell whether the - replacement is correct in every reached use, because values are - computed at definition sites. Therefore, when doing final - substitution of propagated values, we have to check each use - site. Since the RHS of STMT ('b') is different from the LHS of - the originating statement ('*p'), we cannot replace 'b' with - '10'. - - Similarly, when merging values from PHI node arguments, - propagators need to take care not to merge the same values - stored in different locations: - - if (...) - # a_3 = VDEF <a_2> - a.b = 3; - else - # a_4 = VDEF <a_2> - a.c = 3; - # a_5 = PHI <a_3, a_4> - - It would be wrong to propagate '3' into 'a_5' because that - operation merges two stores to different memory locations. - - - 2- If the value to be replaced is an SSA name for a virtual - register, then we simply replace each VUSE operand with its - value from PROP_VALUE. This is the same replacement done by - replace_uses_in. */ - -static bool -replace_vuses_in (gimple stmt, prop_value_t *prop_value) -{ - bool replaced = false; - ssa_op_iter iter; - use_operand_p vuse; - - if (stmt_makes_single_load (stmt)) - { - /* If STMT is an assignment whose RHS is a single memory load, - see if we are trying to propagate a constant or a GIMPLE - register (case #1 above). */ - prop_value_t *val = get_value_loaded_by (stmt, prop_value); - tree rhs = gimple_assign_rhs1 (stmt); - - if (val - && val->value - && (is_gimple_reg (val->value) - || is_gimple_min_invariant (val->value)) - && simple_cst_equal (rhs, val->mem_ref) == 1) - { - /* We can only perform the substitution if the load is done - from the same memory location as the original store. - Since we already know that there are no intervening - stores between DEF_STMT and STMT, we only need to check - that the RHS of STMT is the same as the memory reference - propagated together with the value. */ - gimple_assign_set_rhs1 (stmt, val->value); - - if (TREE_CODE (val->value) != SSA_NAME) - prop_stats.num_const_prop++; - else - prop_stats.num_copy_prop++; - - /* Since we have replaced the whole RHS of STMT, there - is no point in checking the other VUSEs, as they will - all have the same value. */ - return true; - } - } - - /* Otherwise, the values for every VUSE operand must be other - SSA_NAMEs that can be propagated into STMT. */ - FOR_EACH_SSA_USE_OPERAND (vuse, stmt, iter, SSA_OP_VIRTUAL_USES) - { - tree var = USE_FROM_PTR (vuse); - tree val = prop_value[SSA_NAME_VERSION (var)].value; - - if (val == NULL_TREE || var == val) - continue; - - /* Constants and copies propagated between real and virtual - operands are only possible in the cases handled above. They - should be ignored in any other context. */ - if (is_gimple_min_invariant (val) || is_gimple_reg (val)) - continue; - - propagate_value (vuse, val); - prop_stats.num_copy_prop++; - replaced = true; - } - - return replaced; -} - - /* Replace propagated values into all the arguments for PHI using the values from PROP_VALUE. */ @@ -1321,17 +1156,11 @@ substitute_and_fold (prop_value_t *prop_value, bool use_ranges_p) gcc_assert (gsi_stmt (i) == stmt); } - if (prop_value) - { - /* Only replace real uses if we couldn't fold the - statement using value range information (value range - information is not collected on virtuals, so we only - need to check this for real uses). */ - if (!did_replace) - did_replace |= replace_uses_in (stmt, prop_value); - - did_replace |= replace_vuses_in (stmt, prop_value); - } + /* Only replace real uses if we couldn't fold the + statement using value range information. */ + if (prop_value + && !did_replace) + did_replace |= replace_uses_in (stmt, prop_value); /* If we made a replacement, fold and cleanup the statement. */ if (did_replace) |