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builtins.c (expand_builtin): Use expand_builtin_pow to expand calls for pow...

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* builtins.c (expand_builtin): Use expand_builtin_pow to expand
	calls for pow, powf, powl and their __builtin_ variants.
	(expand_builtin_pow): If the second argument is a constant
	integer and compiling with -ffast-math, use expand_powi to
	generate RTL if powi_cost is less than POWI_MAX_MULTS.
	(powi_cost): New function to return the number of multiplications
	necessary to evaluate an Nth power, for integer constant N.
	(expand_powi): New function to expand the RTL for evaluating
	the Nth power of a floating point value, for integer constant N.

	* doc/tm.texi (POWI_MAX_MULTS): Document new target macro.

	* gcc.dg/builtins-24.c: New test case.

From-SVN: r68401
This commit is contained in:
Roger Sayle 2003-06-24 02:20:12 +00:00 committed by Roger Sayle
parent e4048ffc3f
commit 2082e02f41
5 changed files with 318 additions and 0 deletions
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14
gcc/ChangeLog
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@ -1,3 +1,17 @@
2003-06-23 Roger Sayle <roger@eyesopen.com>
* builtins.c (expand_builtin): Use expand_builtin_pow to expand
calls for pow, powf, powl and their __builtin_ variants.
(expand_builtin_pow): If the second argument is a constant
integer and compiling with -ffast-math, use expand_powi to
generate RTL if powi_cost is less than POWI_MAX_MULTS.
(powi_cost): New function to return the number of multiplications
necessary to evaluate an Nth power, for integer constant N.
(expand_powi): New function to expand the RTL for evaluating
the Nth power of a floating point value, for integer constant N.
* doc/tm.texi (POWI_MAX_MULTS): Document new target macro.
Mon Jun 23 23:07:35 CEST 2003 Jan Hubicka <jh@suse.cz>
* cgraph.c (cgraph_nodes_queue): Declare.

254
gcc/builtins.c
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@ -1937,6 +1937,253 @@ expand_builtin_mathfn_2 (tree exp, rtx target, rtx subtarget)
return target;
}
/* To evaluate powi(x,n), the floating point value x raised to the
constant integer exponent n, we use a hybrid algorithm that
combines the "window method" with look-up tables. For an
introduction to exponentiation algorithms and "addition chains",
see section 4.6.3, "Evaluation of Powers" of Donald E. Knuth,
"Seminumerical Algorithms", Vol. 2, "The Art of Computer Programming",
3rd Edition, 1998, and Daniel M. Gordon, "A Survey of Fast Exponentiation
Methods", Journal of Algorithms, Vol. 27, pp. 129-146, 1998. */
/* Provide a default value for POWI_MAX_MULTS, the maximum number of
multiplications to inline before calling the system library's pow
function. powi(x,n) requires at worst 2*bits(n)-2 multiplications,
so this default never requires calling pow, powf or powl. */
#ifndef POWI_MAX_MULTS
#define POWI_MAX_MULTS (2*HOST_BITS_PER_WIDE_INT-2)
#endif
/* The size of the "optimal power tree" lookup table. All
exponents less than this value are simply looked up in the
powi_table below. This threshold is also used to size the
cache of pseudo registers that hold intermediate results. */
#define POWI_TABLE_SIZE 256
/* The size, in bits of the window, used in the "window method"
exponentiation algorithm. This is equivalent to a radix of
(1<<POWI_WINDOW_SIZE) in the corresponding "m-ary method". */
#define POWI_WINDOW_SIZE 3
/* The following table is an efficient representation of an
"optimal power tree". For each value, i, the corresponding
value, j, in the table states than an optimal evaluation
sequence for calculating pow(x,i) can be found by evaluating
pow(x,j)*pow(x,i-j). An optimal power tree for the first
100 integers is given in Knuth's "Seminumerical algorithms". */
static const unsigned char powi_table[POWI_TABLE_SIZE] =
{
0, 1, 1, 2, 2, 3, 3, 4, /* 0 - 7 */
4, 6, 5, 6, 6, 10, 7, 9, /* 8 - 15 */
8, 16, 9, 16, 10, 12, 11, 13, /* 16 - 23 */
12, 17, 13, 18, 14, 24, 15, 26, /* 24 - 31 */
16, 17, 17, 19, 18, 33, 19, 26, /* 32 - 39 */
20, 25, 21, 40, 22, 27, 23, 44, /* 40 - 47 */
24, 32, 25, 34, 26, 29, 27, 44, /* 48 - 55 */
28, 31, 29, 34, 30, 60, 31, 36, /* 56 - 63 */
32, 64, 33, 34, 34, 46, 35, 37, /* 64 - 71 */
36, 65, 37, 50, 38, 48, 39, 69, /* 72 - 79 */
40, 49, 41, 43, 42, 51, 43, 58, /* 80 - 87 */
44, 64, 45, 47, 46, 59, 47, 76, /* 88 - 95 */
48, 65, 49, 66, 50, 67, 51, 66, /* 96 - 103 */
52, 70, 53, 74, 54, 104, 55, 74, /* 104 - 111 */
56, 64, 57, 69, 58, 78, 59, 68, /* 112 - 119 */
60, 61, 61, 80, 62, 75, 63, 68, /* 120 - 127 */
64, 65, 65, 128, 66, 129, 67, 90, /* 128 - 135 */
68, 73, 69, 131, 70, 94, 71, 88, /* 136 - 143 */
72, 128, 73, 98, 74, 132, 75, 121, /* 144 - 151 */
76, 102, 77, 124, 78, 132, 79, 106, /* 152 - 159 */
80, 97, 81, 160, 82, 99, 83, 134, /* 160 - 167 */
84, 86, 85, 95, 86, 160, 87, 100, /* 168 - 175 */
88, 113, 89, 98, 90, 107, 91, 122, /* 176 - 183 */
92, 111, 93, 102, 94, 126, 95, 150, /* 184 - 191 */
96, 128, 97, 130, 98, 133, 99, 195, /* 192 - 199 */
100, 128, 101, 123, 102, 164, 103, 138, /* 200 - 207 */
104, 145, 105, 146, 106, 109, 107, 149, /* 208 - 215 */
108, 200, 109, 146, 110, 170, 111, 157, /* 216 - 223 */
112, 128, 113, 130, 114, 182, 115, 132, /* 224 - 231 */
116, 200, 117, 132, 118, 158, 119, 206, /* 232 - 239 */
120, 240, 121, 162, 122, 147, 123, 152, /* 240 - 247 */
124, 166, 125, 214, 126, 138, 127, 153, /* 248 - 255 */
};
/* Return the number of multiplications required to calculate
powi(x,n) where n is less than POWI_TABLE_SIZE. This is a
subroutine of powi_cost. CACHE is an array indicating
which exponents have already been calculated. */
static int
powi_lookup_cost (unsigned HOST_WIDE_INT n, bool *cache)
{
/* If we've already calculated this exponent, then this evaluation
doesn't require any additional multiplications. */
if (cache[n])
return 0;
cache[n] = true;
return powi_lookup_cost (n - powi_table[n], cache)
+ powi_lookup_cost (powi_table[n], cache) + 1;
}
/* Return the number of multiplications required to calculate
powi(x,n) for an arbitrary x, given the exponent N. This
function needs to be kept in sync with expand_powi below. */
static int
powi_cost (HOST_WIDE_INT n)
{
bool cache[POWI_TABLE_SIZE];
unsigned HOST_WIDE_INT digit;
unsigned HOST_WIDE_INT val;
int result;
if (n == 0)
return 0;
/* Ignore the reciprocal when calculating the cost. */
val = (n < 0) ? -n : n;
/* Initialize the exponent cache. */
memset (cache, 0, POWI_TABLE_SIZE * sizeof (bool));
cache[1] = true;
result = 0;
while (val >= POWI_TABLE_SIZE)
{
if (val & 1)
{
digit = val & ((1 << POWI_WINDOW_SIZE) - 1);
result += powi_lookup_cost (digit, cache)
+ POWI_WINDOW_SIZE + 1;
val >>= POWI_WINDOW_SIZE;
}
else
{
val >>= 1;
result++;
}
}
return result + powi_lookup_cost (n, cache);
}
/* Recursive subroutine of expand_powi. This function takes the array,
CACHE, of already calculated exponents and an exponent N and returns
an RTX that corresponds to CACHE[1]**N, as calculated in mode MODE. */
static rtx
expand_powi_1 (enum machine_mode mode, unsigned HOST_WIDE_INT n, rtx *cache)
{
unsigned HOST_WIDE_INT digit;
rtx target, result;
rtx op0, op1;
if (n < POWI_TABLE_SIZE)
{
if (cache[n])
return cache[n];
target = gen_reg_rtx (mode);
cache[n] = target;
op0 = expand_powi_1 (mode, n - powi_table[n], cache);
op1 = expand_powi_1 (mode, powi_table[n], cache);
}
else if (n & 1)
{
target = gen_reg_rtx (mode);
digit = n & ((1 << POWI_WINDOW_SIZE) - 1);
op0 = expand_powi_1 (mode, n - digit, cache);
op1 = expand_powi_1 (mode, digit, cache);
}
else
{
target = gen_reg_rtx (mode);
op0 = expand_powi_1 (mode, n >> 1, cache);
op1 = op0;
}
result = expand_mult (mode, op0, op1, target, 0);
if (result != target)
emit_move_insn (target, result);
return target;
}
/* Expand the RTL to evaluate powi(x,n) in mode MODE. X is the
floating point operand in mode MODE, and N is the exponent. This
function needs to be kept in sync with powi_cost above. */
static rtx
expand_powi (rtx x, enum machine_mode mode, HOST_WIDE_INT n)
{
unsigned HOST_WIDE_INT val;
rtx cache[POWI_TABLE_SIZE];
rtx result;
if (n == 0)
return CONST1_RTX (mode);
val = (n < 0) ? -n : n;
memset (cache, 0, sizeof(cache));
cache[1] = x;
result = expand_powi_1 (mode, (n < 0) ? -n : n, cache);
/* If the original exponent was negative, reciprocate the result. */
if (n < 0)
result = expand_binop (mode, sdiv_optab, CONST1_RTX (mode),
result, NULL_RTX, 0, OPTAB_LIB_WIDEN);
return result;
}
/* Expand a call to the pow built-in mathematical function. Return 0 if
a normal call should be emitted rather than expanding the function
in-line. EXP is the expression that is a call to the builtin
function; if convenient, the result should be placed in TARGET. */
static rtx
expand_builtin_pow (tree exp, rtx target, rtx subtarget)
{
tree arglist = TREE_OPERAND (exp, 1);
tree arg0, arg1;
if (! validate_arglist (arglist, REAL_TYPE, REAL_TYPE, VOID_TYPE))
return 0;
arg0 = TREE_VALUE (arglist);
arg1 = TREE_VALUE (TREE_CHAIN (arglist));
if (flag_unsafe_math_optimizations
&& ! flag_errno_math
&& ! optimize_size
&& TREE_CODE (arg1) == REAL_CST
&& ! TREE_CONSTANT_OVERFLOW (arg1))
{
REAL_VALUE_TYPE cint;
REAL_VALUE_TYPE c;
HOST_WIDE_INT n;
c = TREE_REAL_CST (arg1);
n = real_to_integer (&c);
real_from_integer (&cint, VOIDmode, n, n < 0 ? -1 : 0, 0);
if (real_identical (&c, &cint)
&& powi_cost (n) <= POWI_MAX_MULTS)
{
enum machine_mode mode = TYPE_MODE (TREE_TYPE (exp));
rtx op = expand_expr (arg0, subtarget, VOIDmode, 0);
op = force_reg (mode, op);
return expand_powi (op, mode, n);
}
}
return expand_builtin_mathfn_2 (exp, target, NULL_RTX);
}
/* Expand expression EXP which is a call to the strlen builtin. Return 0
if we failed the caller should emit a normal call, otherwise
try to get the result in TARGET, if convenient. */
@ -4588,6 +4835,13 @@ expand_builtin (tree exp, rtx target, rtx subtarget, enum machine_mode mode,
case BUILT_IN_POW:
case BUILT_IN_POWF:
case BUILT_IN_POWL:
if (! flag_unsafe_math_optimizations)
break;
target = expand_builtin_pow (exp, target, subtarget);
if (target)
return target;
break;
case BUILT_IN_ATAN2:
case BUILT_IN_ATAN2F:
case BUILT_IN_ATAN2L:

11
gcc/doc/tm.texi
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@ -9155,3 +9155,14 @@ true when @var{after_prologue_epilogue_gen} is false, you still are likely
to have to make special provisions in @code{INITIAL_ELIMINATION_OFFSET}
to reserve space for caller-saved target registers.
@end deftypefn
@defmac POWI_MAX_MULTS
If defined, this macro is interpreted as a signed integer C expression
that specifies the maximum number of floating point multiplications
that should be emitted when expanding exponentiation by an integer
constant inline. When this value is defined, exponentiation requiring
more than this number of multiplications is implemented by calling the
system library's @code{pow}, @code{powf} or @code{powl} routines.
The default value places no upper bound on the multiplication count.
@end defmac

4
gcc/testsuite/ChangeLog
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@ -1,3 +1,7 @@
2003-06-23 Roger Sayle <roger@eyesopen.com>
* gcc.dg/builtins-24.c: New test case.
2003-06-23 Jakub Jelinek <jakub@redhat.com>
* g++.dg/opt/operator1.C: New test.

35
gcc/testsuite/gcc.dg/builtins-24.c Normal file
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@ -0,0 +1,35 @@
/* Copyright (C) 2003 Free Software Foundation.
Check that the RTL expansion of floating point exponentiation by
a constant integer doesn't break anything and produces the expected
results.
Written by Roger Sayle, 20th June 2003. */
/* { dg-do run } */
/* { dg-options "-O2 -ffast-math" } */
extern double pow(double,double);
extern void abort(void);
double foo (double x)
{
return pow (x, 6);
}
double bar (double x)
{
return pow (x, -4);
}
int main()
{
if (foo (2.0) != 64.0)
abort ();
if (bar (2.0) != 0.0625)
abort ();
return 0;
}