}
-/* 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
}
-/* 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
{
}
-/* 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. */
{
bool did_replace;
gimple stmt = gsi_stmt (i);
+ gimple old_stmt;
enum gimple_code code = gimple_code (stmt);
/* Ignore ASSERT_EXPRs. They are used by VRP to generate
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 we made a replacement, fold the statement. */
+
+ old_stmt = stmt;
if (did_replace)
- {
- gimple old_stmt = stmt;
+ fold_stmt (&i);
+
+ /* Some statements may be simplified using ranges. For
+ example, division may be replaced by shifts, modulo
+ replaced with bitwise and, etc. Do this after
+ substituting constants, folding, etc so that we're
+ presented with a fully propagated, canonicalized
+ statement. */
+ if (use_ranges_p)
+ did_replace |= simplify_stmt_using_ranges (&i);
- fold_stmt (&i);
+ /* Now cleanup. */
+ if (did_replace)
+ {
stmt = gsi_stmt (i);
/* If we cleaned up EH information from the statement,
fprintf (dump_file, "Not folded\n");
}
- /* Some statements may be simplified using ranges. For
- example, division may be replaced by shifts, modulo
- replaced with bitwise and, etc. Do this after
- substituting constants, folding, etc so that we're
- presented with a fully propagated, canonicalized
- statement. */
- if (use_ranges_p)
- simplify_stmt_using_ranges (stmt);
-
gsi_prev (&i);
}
}
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