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| static vec< cluster * > | find_bit_tests_fast (vec< cluster * > &clusters) |
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| static vec< cluster * > | find_bit_tests_slow (vec< cluster * > &clusters) |
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| static vec< cluster * > | find_bit_tests (vec< cluster * > &clusters, int max_c) |
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| static bool | can_be_handled (unsigned HOST_WIDE_INT range, unsigned uniq) |
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| static bool | can_be_handled (const vec< cluster * > &clusters, unsigned start, unsigned end) |
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| static bool | is_beneficial (unsigned count, unsigned uniq) |
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| static bool | is_beneficial (const vec< cluster * > &clusters, unsigned start, unsigned end) |
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| static basic_block | hoist_edge_and_branch_if_true (gimple_stmt_iterator *gsip, tree cond, basic_block case_bb, profile_probability prob, location_t) |
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| static bool | is_enabled (void) |
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| static unsigned HOST_WIDE_INT | get_range (tree low, tree high) |
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A GIMPLE switch statement can be expanded to a short sequence of bit-wise
comparisons. "switch(x)" is converted into "if ((1 << (x-MINVAL)) & CST)"
where CST and MINVAL are integer constants. This is better than a series
of compare-and-branch insns in some cases, e.g. we can implement:
if ((x==4) || (x==6) || (x==9) || (x==11))
as a single bit test:
if ((1<<x) & ((1<<4)|(1<<6)|(1<<9)|(1<<11)))
This transformation is only applied if the number of case targets is small,
if CST constains at least 3 bits, and "1 << x" is cheap. The bit tests are
performed in "word_mode".
The following example shows the code the transformation generates:
int bar(int x)
{
switch (x)
{
case '0': case '1': case '2': case '3': case '4':
case '5': case '6': case '7': case '8': case '9':
case 'A': case 'B': case 'C': case 'D': case 'E':
case 'F':
return 1;
}
return 0;
}
==>
bar (int x)
{
tmp1 = x - 48;
if (tmp1 > (70 - 48)) goto L2;
tmp2 = 1 << tmp1;
tmp3 = 0b11111100000001111111111;
if ((tmp2 & tmp3) != 0) goto L1 ; else goto L2;
L1:
return 1;
L2:
return 0;
}
TODO: There are still some improvements to this transformation that could
be implemented:
* A narrower mode than word_mode could be used if that is cheaper, e.g.
for x86_64 where a narrower-mode shift may result in smaller code.
* The compounded constant could be shifted rather than the one. The
test would be either on the sign bit or on the least significant bit,
depending on the direction of the shift. On some machines, the test
for the branch would be free if the bit to test is already set by the
shift operation.
This transformation was contributed by Roger Sayle, see this e-mail:
http://gcc.gnu.org/ml/gcc-patches/2003-01/msg01950.html
| void bit_test_cluster::emit |
( |
tree | index_expr, |
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tree | index_type, |
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tree | default_label_expr, |
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basic_block | default_bb, |
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location_t | loc ) |
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finaloverridevirtual |
Expand a switch statement by a short sequence of bit-wise
comparisons. "switch(x)" is effectively converted into
"if ((1 << (x-MINVAL)) & CST)" where CST and MINVAL are
integer constants.
INDEX_EXPR is the value being switched on.
MINVAL is the lowest case value of in the case nodes,
and RANGE is highest value minus MINVAL. MINVAL and RANGE
are not guaranteed to be of the same type as INDEX_EXPR
(the gimplifier doesn't change the type of case label values,
and MINVAL and RANGE are derived from those values).
MAXVAL is MINVAL + RANGE.
There *MUST* be max_case_bit_tests or less unique case
node targets.
Implements tree_switch_conversion::cluster.
References profile_probability::always(), tree_switch_conversion::case_bit_test::bits, boolean_type_node, build_zero_cst(), cfun, tree_switch_conversion::case_bit_test::cmp(), compare_tree_int(), count, EDGE_COUNT, fold_build2, fold_build2_loc(), fold_convert, fold_convert_loc(), force_gimple_operand_gsi(), gcc_assert, gcc_checking_assert, GEN_INT, gen_raw_REG(), tree_switch_conversion::group_cluster::get_high(), tree_switch_conversion::simple_cluster::get_high(), tree_switch_conversion::group_cluster::get_low(), tree_switch_conversion::simple_cluster::get_low(), tree_switch_conversion::cluster::get_range(), get_range_query(), gimple_build_assign(), gsi_bb(), gsi_insert_before(), gsi_last_bb(), GSI_SAME_STMT, wi::gt_p(), hoist_edge_and_branch_if_true(), i, immed_wide_int_const(), profile_probability::initialized_p(), int_const_binop(), integer_one_node, integer_zero_node, profile_probability::invert(), tree_switch_conversion::case_bit_test::label, wi::leu_p(), wi::lrshift(), wi::lshift(), wi::lt_p(), tree_switch_conversion::cluster::m_case_bb, tree_switch_conversion::cluster::m_case_label_expr, tree_switch_conversion::group_cluster::m_cases, tree_switch_conversion::cluster::m_default_prob, m_handles_entire_switch, m_max_case_bit_tests, tree_switch_conversion::cluster::m_prob, tree_switch_conversion::cluster::m_subtree_prob, make_edge(), make_ssa_name(), tree_switch_conversion::case_bit_test::mask, profile_probability::never(), NULL_TREE, wi::one(), optimize_insn_for_speed_p(), tree_switch_conversion::case_bit_test::prob, qsort, r, range_check_type(), set_src_cost(), tree_switch_conversion::case_bit_test::target_bb, wi::to_wide(), TREE_CODE, tree_to_uhwi(), TREE_TYPE, lang_hooks_for_types::type_for_mode, TYPE_PRECISION, TYPE_SIGN, lang_hooks::types, update_stmt(), wide_int_to_tree(), word_mode, and wi::zero().
Find bit tests of given CLUSTERS, where all members of the vector are of
type simple_cluster. Use a fast algorithm that might not find the optimal
solution (minimal number of clusters on the output). New clusters are
returned.
You should call find_bit_tests () instead of calling this function
directly.
References hash_set< KeyId, Lazy, Traits >::add(), BITS_PER_WORD, hash_set< KeyId, Lazy, Traits >::contains(), hash_set< KeyId, Lazy, Traits >::elements(), tree_switch_conversion::cluster::get_high(), tree_switch_conversion::cluster::get_low(), tree_switch_conversion::cluster::get_range(), i, is_beneficial(), tree_switch_conversion::cluster::m_case_bb, and m_max_case_bit_tests.
Referenced by find_bit_tests().
Find bit tests of given CLUSTERS, where all members of the vector
are of type simple_cluster. Use a slow (quadratic) algorithm that always
finds the optimal solution (minimal number of clusters on the output). New
clusters are returned.
You should call find_bit_tests () instead of calling this function
directly.
References can_be_handled(), end(), gcc_checking_assert, i, INT_MAX, and is_beneficial().
Referenced by find_bit_tests().
Split the basic block at the statement pointed to by GSIP, and insert
a branch to the target basic block of E_TRUE conditional on tree
expression COND.
It is assumed that there is already an edge from the to-be-split
basic block to E_TRUE->dest block. This edge is removed, and the
profile information on the edge is re-used for the new conditional
jump.
The CFG is updated. The dominator tree will not be valid after
this transformation, but the immediate dominators are updated if
UPDATE_DOMINATORS is true.
Returns the newly created basic block.
References basic_block_def::count, force_gimple_operand_gsi(), gcc_assert, gimple_build_cond_from_tree(), gimple_set_location(), gsi_bb(), gsi_insert_before(), GSI_SAME_STMT, make_edge(), NULL, NULL_TREE, redirect_edge_pred(), and split_block().
Referenced by emit().
