Support common idioms for count trailing zeroes using an array lookup.
The canonical form is array[((x & -x) * C) >> SHIFT] where C is a magic
constant which when multiplied by a power of 2 creates a unique value
in the top 5 or 6 bits. This is then indexed into a table which maps it
to the number of trailing zeroes. When the table is valid, we emit a
sequence using the target defined value for ctz (0):
int ctz1 (unsigned x)
{
static const char table[32] =
{
0, 1, 28, 2, 29, 14, 24, 3, 30, 22, 20, 15, 25, 17, 4, 8,
31, 27, 13, 23, 21, 19, 16, 7, 26, 12, 18, 6, 11, 5, 10, 9
};
return table[((unsigned)((x & -x) * 0x077CB531U)) >> 27];
}
Is optimized to:
rbit w0, w0
clz w0, w0
and w0, w0, 31
ret
gcc/
PR tree-optimization/90838
* tree-ssa-forwprop.c (check_ctz_array): Add new function.
(check_ctz_string): Likewise.
(optimize_count_trailing_zeroes): Likewise.
(simplify_count_trailing_zeroes): Likewise.
(pass_forwprop::execute): Try ctz simplification.
* match.pd: Add matching for ctz idioms.
testsuite/
PR tree-optimization/90838
* testsuite/gcc.target/aarch64/pr90838.c: New test.
From-SVN: r280132
+2020-01-10 Wilco Dijkstra <wdijkstr@arm.com>
+
+ PR tree-optimization/90838
+ * tree-ssa-forwprop.c (check_ctz_array): Add new function.
+ (check_ctz_string): Likewise.
+ (optimize_count_trailing_zeroes): Likewise.
+ (simplify_count_trailing_zeroes): Likewise.
+ (pass_forwprop::execute): Try ctz simplification.
+ * match.pd: Add matching for ctz idioms.
+
2020-01-10 Stam Markianos-Wright <stam.markianos-wright@arm.com>
* config/aarch64/aarch64.c (aarch64_invalid_conversion): New function
(simplify
(vec_perm vec_same_elem_p@0 @0 @1)
@0)
+
+/* Match count trailing zeroes for simplify_count_trailing_zeroes in fwprop.
+ The canonical form is array[((x & -x) * C) >> SHIFT] where C is a magic
+ constant which when multiplied by a power of 2 contains a unique value
+ in the top 5 or 6 bits. This is then indexed into a table which maps it
+ to the number of trailing zeroes. */
+(match (ctz_table_index @1 @2 @3)
+ (rshift (mult (bit_and:c (negate @1) @1) INTEGER_CST@2) INTEGER_CST@3))
+2020-01-10 Wilco Dijkstra <wdijkstr@arm.com>
+
+ * testsuite/gcc.target/aarch64/pr90838.c: New test.
+
2020-01-10 Stam Markianos-Wright <stam.markianos-wright@arm.com>
* g++.target/aarch64/bfloat_cpp_typecheck.C: New test.
--- /dev/null
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+int ctz1 (unsigned x)
+{
+ static const char table[32] =
+ {
+ 0, 1, 28, 2, 29, 14, 24, 3, 30, 22, 20, 15, 25, 17, 4, 8,
+ 31, 27, 13, 23, 21, 19, 16, 7, 26, 12, 18, 6, 11, 5, 10, 9
+ };
+
+ return table[((unsigned)((x & -x) * 0x077CB531U)) >> 27];
+}
+
+int ctz2 (unsigned x)
+{
+ const int u = 0;
+ static short table[64] =
+ {
+ 32, 0, 1,12, 2, 6, u,13, 3, u, 7, u, u, u, u,14,
+ 10, 4, u, u, 8, u, u,25, u, u, u, u, u,21,27,15,
+ 31,11, 5, u, u, u, u, u, 9, u, u,24, u, u,20,26,
+ 30, u, u, u, u,23, u,19,29, u,22,18,28,17,16, u
+ };
+
+ x = (x & -x) * 0x0450FBAF;
+ return table[x >> 26];
+}
+
+int ctz3 (unsigned x)
+{
+ static int table[32] =
+ {
+ 0, 1, 2,24, 3,19, 6,25, 22, 4,20,10,16, 7,12,26,
+ 31,23,18, 5,21, 9,15,11,30,17, 8,14,29,13,28,27
+ };
+
+ if (x == 0) return 32;
+ x = (x & -x) * 0x04D7651F;
+ return table[x >> 27];
+}
+
+static const unsigned long long magic = 0x03f08c5392f756cdULL;
+
+static const char table[64] = {
+ 0, 1, 12, 2, 13, 22, 17, 3,
+ 14, 33, 23, 36, 18, 58, 28, 4,
+ 62, 15, 34, 26, 24, 48, 50, 37,
+ 19, 55, 59, 52, 29, 44, 39, 5,
+ 63, 11, 21, 16, 32, 35, 57, 27,
+ 61, 25, 47, 49, 54, 51, 43, 38,
+ 10, 20, 31, 56, 60, 46, 53, 42,
+ 9, 30, 45, 41, 8, 40, 7, 6,
+};
+
+int ctz4 (unsigned long x)
+{
+ unsigned long lsb = x & -x;
+ return table[(lsb * magic) >> 58];
+}
+
+/* { dg-final { scan-assembler-times "clz\t" 4 } } */
+/* { dg-final { scan-assembler-times "and\t" 2 } } */
+/* { dg-final { scan-assembler-not "cmp\t.*0" } } */
#include "optabs-tree.h"
#include "tree-vector-builder.h"
#include "vec-perm-indices.h"
+#include "internal-fn.h"
+#include "cgraph.h"
/* This pass propagates the RHS of assignment statements into use
sites of the LHS of the assignment. It's basically a specialized
return true;
}
+
+/* Check whether an array contains a valid ctz table. */
+static bool
+check_ctz_array (tree ctor, unsigned HOST_WIDE_INT mulc,
+ HOST_WIDE_INT &zero_val, unsigned shift, unsigned bits)
+{
+ tree elt, idx;
+ unsigned HOST_WIDE_INT i, mask;
+ unsigned matched = 0;
+
+ mask = ((HOST_WIDE_INT_1U << (bits - shift)) - 1) << shift;
+
+ zero_val = 0;
+
+ FOR_EACH_CONSTRUCTOR_ELT (CONSTRUCTOR_ELTS (ctor), i, idx, elt)
+ {
+ if (TREE_CODE (idx) != INTEGER_CST || TREE_CODE (elt) != INTEGER_CST)
+ return false;
+ if (i > bits * 2)
+ return false;
+
+ unsigned HOST_WIDE_INT index = tree_to_shwi (idx);
+ HOST_WIDE_INT val = tree_to_shwi (elt);
+
+ if (index == 0)
+ {
+ zero_val = val;
+ matched++;
+ }
+
+ if (val >= 0 && val < bits && (((mulc << val) & mask) >> shift) == index)
+ matched++;
+
+ if (matched > bits)
+ return true;
+ }
+
+ return false;
+}
+
+/* Check whether a string contains a valid ctz table. */
+static bool
+check_ctz_string (tree string, unsigned HOST_WIDE_INT mulc,
+ HOST_WIDE_INT &zero_val, unsigned shift, unsigned bits)
+{
+ unsigned HOST_WIDE_INT len = TREE_STRING_LENGTH (string);
+ unsigned HOST_WIDE_INT mask;
+ unsigned matched = 0;
+ const unsigned char *p = (const unsigned char *) TREE_STRING_POINTER (string);
+
+ if (len < bits || len > bits * 2)
+ return false;
+
+ mask = ((HOST_WIDE_INT_1U << (bits - shift)) - 1) << shift;
+
+ zero_val = p[0];
+
+ for (unsigned i = 0; i < len; i++)
+ if (p[i] < bits && (((mulc << p[i]) & mask) >> shift) == i)
+ matched++;
+
+ return matched == bits;
+}
+
+/* Recognize count trailing zeroes idiom.
+ The canonical form is array[((x & -x) * C) >> SHIFT] where C is a magic
+ constant which when multiplied by a power of 2 creates a unique value
+ in the top 5 or 6 bits. This is then indexed into a table which maps it
+ to the number of trailing zeroes. Array[0] is returned so the caller can
+ emit an appropriate sequence depending on whether ctz (0) is defined on
+ the target. */
+static bool
+optimize_count_trailing_zeroes (tree array_ref, tree x, tree mulc,
+ tree tshift, HOST_WIDE_INT &zero_val)
+{
+ tree type = TREE_TYPE (array_ref);
+ tree array = TREE_OPERAND (array_ref, 0);
+
+ gcc_assert (TREE_CODE (mulc) == INTEGER_CST);
+ gcc_assert (TREE_CODE (tshift) == INTEGER_CST);
+
+ tree input_type = TREE_TYPE (x);
+ unsigned input_bits = tree_to_shwi (TYPE_SIZE (input_type));
+
+ /* Check the array is not wider than integer type and the input is a 32-bit
+ or 64-bit type. */
+ if (TYPE_PRECISION (type) > 32)
+ return false;
+ if (input_bits != 32 && input_bits != 64)
+ return false;
+
+ if (!direct_internal_fn_supported_p (IFN_CTZ, input_type, OPTIMIZE_FOR_BOTH))
+ return false;
+
+ /* Check the lower bound of the array is zero. */
+ tree low = array_ref_low_bound (array_ref);
+ if (!low || !integer_zerop (low))
+ return false;
+
+ unsigned shiftval = tree_to_uhwi (tshift);
+
+ /* Check the shift extracts the top 5..7 bits. */
+ if (shiftval < input_bits - 7 || shiftval > input_bits - 5)
+ return false;
+
+ tree ctor = ctor_for_folding (array);
+ if (!ctor)
+ return false;
+
+ unsigned HOST_WIDE_INT val = tree_to_uhwi (mulc);
+
+ if (TREE_CODE (ctor) == CONSTRUCTOR)
+ return check_ctz_array (ctor, val, zero_val, shiftval, input_bits);
+
+ if (TREE_CODE (ctor) == STRING_CST)
+ return check_ctz_string (ctor, val, zero_val, shiftval, input_bits);
+
+ return false;
+}
+
+/* Match.pd function to match the ctz expression. */
+extern bool gimple_ctz_table_index (tree, tree *, tree (*)(tree));
+
+static bool
+simplify_count_trailing_zeroes (gimple_stmt_iterator *gsi)
+{
+ gimple *stmt = gsi_stmt (*gsi);
+ tree array_ref = gimple_assign_rhs1 (stmt);
+ tree res_ops[3];
+ HOST_WIDE_INT zero_val;
+
+ gcc_checking_assert (TREE_CODE (array_ref) == ARRAY_REF);
+
+ if (!gimple_ctz_table_index (TREE_OPERAND (array_ref, 1), &res_ops[0], NULL))
+ return false;
+
+ if (optimize_count_trailing_zeroes (array_ref, res_ops[0],
+ res_ops[1], res_ops[2], zero_val))
+ {
+ tree type = TREE_TYPE (res_ops[0]);
+ HOST_WIDE_INT ctzval;
+ HOST_WIDE_INT type_size = tree_to_shwi (TYPE_SIZE (type));
+ bool zero_ok = CTZ_DEFINED_VALUE_AT_ZERO (TYPE_MODE (type), ctzval) == 2;
+
+ /* Skip if there is no value defined at zero, or if we can't easily
+ return the correct value for zero. */
+ if (!zero_ok)
+ return false;
+ if (zero_val != ctzval && !(zero_val == 0 && ctzval == type_size))
+ return false;
+
+ gimple_seq seq = NULL;
+ gimple *g;
+ gcall *call = gimple_build_call_internal (IFN_CTZ, 1, res_ops[0]);
+ gimple_set_location (call, gimple_location (stmt));
+ gimple_set_lhs (call, make_ssa_name (integer_type_node));
+ gimple_seq_add_stmt (&seq, call);
+
+ tree prev_lhs = gimple_call_lhs (call);
+
+ /* Emit ctz (x) & 31 if ctz (0) is 32 but we need to return 0. */
+ if (zero_val == 0 && ctzval == type_size)
+ {
+ g = gimple_build_assign (make_ssa_name (integer_type_node),
+ BIT_AND_EXPR, prev_lhs,
+ build_int_cst (integer_type_node,
+ type_size - 1));
+ gimple_set_location (g, gimple_location (stmt));
+ gimple_seq_add_stmt (&seq, g);
+ prev_lhs = gimple_assign_lhs (g);
+ }
+
+ g = gimple_build_assign (gimple_assign_lhs (stmt), NOP_EXPR, prev_lhs);
+ gimple_seq_add_stmt (&seq, g);
+ gsi_replace_with_seq (gsi, seq, true);
+ return true;
+ }
+
+ return false;
+}
+
+
/* Combine an element access with a shuffle. Returns true if there were
any changes made, else it returns false. */
else if (code == CONSTRUCTOR
&& TREE_CODE (TREE_TYPE (rhs1)) == VECTOR_TYPE)
changed = simplify_vector_constructor (&gsi);
+ else if (code == ARRAY_REF)
+ changed = simplify_count_trailing_zeroes (&gsi);
break;
}
projects / gcc.git / commitdiff