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glibc/sysdeps/i386/fpu/fenv_private.h
Siddhesh Poyarekar 2506109403 Set/restore rounding mode only when needed 
The most common use case of math functions is with default rounding
mode, i.e. rounding to nearest.  Setting and restoring rounding mode
is an unnecessary overhead for this, so I've added support for a
context, which does the set/restore only if the FP status needs a
change.  The code is written such that only x86 uses these.  Other
architectures should be unaffected by it, but would definitely benefit
if the set/restore has as much overhead relative to the rest of the
code, as the x86 bits do.

Here's a summary of the performance improvement due to these
improvements; I've only mentioned functions that use the set/restore
and have benchmark inputs for x86_64:

Before:

cos(): ITERS:4.69335e+08: TOTAL:28884.6Mcy, MAX:4080.28cy, MIN:57.562cy, 16248.6 calls/Mcy
exp(): ITERS:4.47604e+08: TOTAL:28796.2Mcy, MAX:207.721cy, MIN:62.385cy, 15543.9 calls/Mcy
pow(): ITERS:1.63485e+08: TOTAL:28879.9Mcy, MAX:362.255cy, MIN:172.469cy, 5660.86 calls/Mcy
sin(): ITERS:3.89578e+08: TOTAL:28900Mcy, MAX:704.859cy, MIN:47.583cy, 13480.2 calls/Mcy
tan(): ITERS:7.0971e+07: TOTAL:28902.2Mcy, MAX:1357.79cy, MIN:388.58cy, 2455.55 calls/Mcy

After:

cos(): ITERS:6.0014e+08: TOTAL:28875.9Mcy, MAX:364.283cy, MIN:45.716cy, 20783.4 calls/Mcy
exp(): ITERS:5.48578e+08: TOTAL:28764.9Mcy, MAX:191.617cy, MIN:51.011cy, 19071.1 calls/Mcy
pow(): ITERS:1.70013e+08: TOTAL:28873.6Mcy, MAX:689.522cy, MIN:163.989cy, 5888.18 calls/Mcy
sin(): ITERS:4.64079e+08: TOTAL:28891.5Mcy, MAX:6959.3cy, MIN:36.189cy, 16062.8 calls/Mcy
tan(): ITERS:7.2354e+07: TOTAL:28898.9Mcy, MAX:1295.57cy, MIN:380.698cy, 2503.7 calls/Mcy

So the improvements are:

cos: 27.9089%
exp: 22.6919%
pow: 4.01564%
sin: 19.1585%
tan: 1.96086%

The downside of the change is that it will have an adverse performance
impact on non-default rounding modes, but I think the tradeoff is
justified.
2013-06-12 10:36:48 +05:30

501 lines
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#ifndef FENV_PRIVATE_H
#define FENV_PRIVATE_H 1
#include <fenv.h>
#include <fpu_control.h>
#ifdef __SSE2_MATH__
# define math_opt_barrier(x) \
({ __typeof(x) __x; \
if (sizeof (x) <= sizeof (double)) \
__asm ("" : "=x" (__x) : "0" (x)); \
else \
__asm ("" : "=t" (__x) : "0" (x)); \
__x; })
# define math_force_eval(x) \
do { \
if (sizeof (x) <= sizeof (double)) \
__asm __volatile ("" : : "x" (x)); \
else \
__asm __volatile ("" : : "f" (x)); \
} while (0)
#else
# define math_opt_barrier(x) \
({ __typeof (x) __x; \
__asm ("" : "=t" (__x) : "0" (x)); \
__x; })
# define math_force_eval(x) \
do { \
__typeof (x) __x = (x); \
if (sizeof (x) <= sizeof (double)) \
__asm __volatile ("" : : "m" (__x)); \
else \
__asm __volatile ("" : : "f" (__x)); \
} while (0)
#endif
/* This file is used by both the 32- and 64-bit ports. The 64-bit port
has a field in the fenv_t for the mxcsr; the 32-bit port does not.
Instead, we (ab)use the only 32-bit field extant in the struct. */
#ifndef __x86_64__
# define __mxcsr __eip
#endif
/* All of these functions are private to libm, and are all used in pairs
to save+change the fp state and restore the original state. Thus we
need not care for both the 387 and the sse unit, only the one we're
actually using. */
#if defined __AVX__ || defined SSE2AVX
# define STMXCSR "vstmxcsr"
# define LDMXCSR "vldmxcsr"
#else
# define STMXCSR "stmxcsr"
# define LDMXCSR "ldmxcsr"
#endif
static __always_inline void
libc_feholdexcept_sse (fenv_t *e)
{
unsigned int mxcsr;
asm (STMXCSR " %0" : "=m" (*&mxcsr));
e->__mxcsr = mxcsr;
mxcsr = (mxcsr | 0x1f80) & ~0x3f;
asm volatile (LDMXCSR " %0" : : "m" (*&mxcsr));
}
static __always_inline void
libc_feholdexcept_387 (fenv_t *e)
{
/* Recall that fnstenv has a side-effect of masking exceptions.
Clobber all of the fp registers so that the TOS field is 0. */
asm volatile ("fnstenv %0; fnclex"
: "=m"(*e)
: : "st", "st(1)", "st(2)", "st(3)",
"st(4)", "st(5)", "st(6)", "st(7)");
}
static __always_inline void
libc_fesetround_sse (int r)
{
unsigned int mxcsr;
asm (STMXCSR " %0" : "=m" (*&mxcsr));
mxcsr = (mxcsr & ~0x6000) | (r << 3);
asm volatile (LDMXCSR " %0" : : "m" (*&mxcsr));
}
static __always_inline void
libc_fesetround_387 (int r)
{
fpu_control_t cw;
_FPU_GETCW (cw);
cw = (cw & ~0xc00) | r;
_FPU_SETCW (cw);
}
static __always_inline void
libc_feholdexcept_setround_sse (fenv_t *e, int r)
{
unsigned int mxcsr;
asm (STMXCSR " %0" : "=m" (*&mxcsr));
e->__mxcsr = mxcsr;
mxcsr = ((mxcsr | 0x1f80) & ~0x603f) | (r << 3);
asm volatile (LDMXCSR " %0" : : "m" (*&mxcsr));
}
/* Set both rounding mode and precision. A convenience function for use
by libc_feholdexcept_setround and libc_feholdexcept_setround_53bit. */
static __always_inline void
libc_feholdexcept_setround_387_prec (fenv_t *e, int r)
{
libc_feholdexcept_387 (e);
fpu_control_t cw = e->__control_word;
cw &= ~(_FPU_RC_ZERO | _FPU_EXTENDED);
cw |= r | 0x3f;
_FPU_SETCW (cw);
}
static __always_inline void
libc_feholdexcept_setround_387 (fenv_t *e, int r)
{
libc_feholdexcept_setround_387_prec (e, r | _FPU_EXTENDED);
}
static __always_inline void
libc_feholdexcept_setround_387_53bit (fenv_t *e, int r)
{
libc_feholdexcept_setround_387_prec (e, r | _FPU_DOUBLE);
}
static __always_inline int
libc_fetestexcept_sse (int e)
{
unsigned int mxcsr;
asm volatile (STMXCSR " %0" : "=m" (*&mxcsr));
return mxcsr & e & FE_ALL_EXCEPT;
}
static __always_inline int
libc_fetestexcept_387 (int ex)
{
fexcept_t temp;
asm volatile ("fnstsw %0" : "=a" (temp));
return temp & ex & FE_ALL_EXCEPT;
}
static __always_inline void
libc_fesetenv_sse (fenv_t *e)
{
asm volatile (LDMXCSR " %0" : : "m" (e->__mxcsr));
}
static __always_inline void
libc_fesetenv_387 (fenv_t *e)
{
/* Clobber all fp registers so that the TOS value we saved earlier is
compatible with the current state of the compiler. */
asm volatile ("fldenv %0"
: : "m" (*e)
: "st", "st(1)", "st(2)", "st(3)",
"st(4)", "st(5)", "st(6)", "st(7)");
}
static __always_inline int
libc_feupdateenv_test_sse (fenv_t *e, int ex)
{
unsigned int mxcsr, old_mxcsr, cur_ex;
asm volatile (STMXCSR " %0" : "=m" (*&mxcsr));
cur_ex = mxcsr & FE_ALL_EXCEPT;
/* Merge current exceptions with the old environment. */
old_mxcsr = e->__mxcsr;
mxcsr = old_mxcsr | cur_ex;
asm volatile (LDMXCSR " %0" : : "m" (*&mxcsr));
/* Raise SIGFPE for any new exceptions since the hold. Expect that
the normal environment has all exceptions masked. */
if (__glibc_unlikely (~(old_mxcsr >> 7) & cur_ex))
__feraiseexcept (cur_ex);
/* Test for exceptions raised since the hold. */
return cur_ex & ex;
}
static __always_inline int
libc_feupdateenv_test_387 (fenv_t *e, int ex)
{
fexcept_t cur_ex;
/* Save current exceptions. */
asm volatile ("fnstsw %0" : "=a" (cur_ex));
cur_ex &= FE_ALL_EXCEPT;
/* Reload original environment. */
libc_fesetenv_387 (e);
/* Merge current exceptions. */
__feraiseexcept (cur_ex);
/* Test for exceptions raised since the hold. */
return cur_ex & ex;
}
static __always_inline void
libc_feupdateenv_sse (fenv_t *e)
{
libc_feupdateenv_test_sse (e, 0);
}
static __always_inline void
libc_feupdateenv_387 (fenv_t *e)
{
libc_feupdateenv_test_387 (e, 0);
}
static __always_inline void
libc_feholdsetround_sse (fenv_t *e, int r)
{
unsigned int mxcsr;
asm (STMXCSR " %0" : "=m" (*&mxcsr));
e->__mxcsr = mxcsr;
mxcsr = (mxcsr & ~0x6000) | (r << 3);
asm volatile (LDMXCSR " %0" : : "m" (*&mxcsr));
}
static __always_inline void
libc_feholdsetround_387_prec (fenv_t *e, int r)
{
fpu_control_t cw;
_FPU_GETCW (cw);
e->__control_word = cw;
cw &= ~(_FPU_RC_ZERO | _FPU_EXTENDED);
cw |= r;
_FPU_SETCW (cw);
}
static __always_inline void
libc_feholdsetround_387 (fenv_t *e, int r)
{
libc_feholdsetround_387_prec (e, r | _FPU_EXTENDED);
}
static __always_inline void
libc_feholdsetround_387_53bit (fenv_t *e, int r)
{
libc_feholdsetround_387_prec (e, r | _FPU_DOUBLE);
}
static __always_inline void
libc_feresetround_sse (fenv_t *e)
{
unsigned int mxcsr;
asm (STMXCSR " %0" : "=m" (*&mxcsr));
mxcsr = (mxcsr & ~0x6000) | (e->__mxcsr & 0x6000);
asm volatile (LDMXCSR " %0" : : "m" (*&mxcsr));
}
static __always_inline void
libc_feresetround_387 (fenv_t *e)
{
_FPU_SETCW (e->__control_word);
}
#ifdef __SSE_MATH__
# define libc_feholdexceptf libc_feholdexcept_sse
# define libc_fesetroundf libc_fesetround_sse
# define libc_feholdexcept_setroundf libc_feholdexcept_setround_sse
# define libc_fetestexceptf libc_fetestexcept_sse
# define libc_fesetenvf libc_fesetenv_sse
# define libc_feupdateenv_testf libc_feupdateenv_test_sse
# define libc_feupdateenvf libc_feupdateenv_sse
# define libc_feholdsetroundf libc_feholdsetround_sse
# define libc_feresetroundf libc_feresetround_sse
#else
# define libc_feholdexceptf libc_feholdexcept_387
# define libc_fesetroundf libc_fesetround_387
# define libc_feholdexcept_setroundf libc_feholdexcept_setround_387
# define libc_fetestexceptf libc_fetestexcept_387
# define libc_fesetenvf libc_fesetenv_387
# define libc_feupdateenv_testf libc_feupdateenv_test_387
# define libc_feupdateenvf libc_feupdateenv_387
# define libc_feholdsetroundf libc_feholdsetround_387
# define libc_feresetroundf libc_feresetround_387
#endif /* __SSE_MATH__ */
#ifdef __SSE2_MATH__
# define libc_feholdexcept libc_feholdexcept_sse
# define libc_fesetround libc_fesetround_sse
# define libc_feholdexcept_setround libc_feholdexcept_setround_sse
# define libc_fetestexcept libc_fetestexcept_sse
# define libc_fesetenv libc_fesetenv_sse
# define libc_feupdateenv_test libc_feupdateenv_test_sse
# define libc_feupdateenv libc_feupdateenv_sse
# define libc_feholdsetround libc_feholdsetround_sse
# define libc_feresetround libc_feresetround_sse
#else
# define libc_feholdexcept libc_feholdexcept_387
# define libc_fesetround libc_fesetround_387
# define libc_feholdexcept_setround libc_feholdexcept_setround_387
# define libc_fetestexcept libc_fetestexcept_387
# define libc_fesetenv libc_fesetenv_387
# define libc_feupdateenv_test libc_feupdateenv_test_387
# define libc_feupdateenv libc_feupdateenv_387
# define libc_feholdsetround libc_feholdsetround_387
# define libc_feresetround libc_feresetround_387
#endif /* __SSE2_MATH__ */
#define libc_feholdexceptl libc_feholdexcept_387
#define libc_fesetroundl libc_fesetround_387
#define libc_feholdexcept_setroundl libc_feholdexcept_setround_387
#define libc_fetestexceptl libc_fetestexcept_387
#define libc_fesetenvl libc_fesetenv_387
#define libc_feupdateenv_testl libc_feupdateenv_test_387
#define libc_feupdateenvl libc_feupdateenv_387
#define libc_feholdsetroundl libc_feholdsetround_387
#define libc_feresetroundl libc_feresetround_387
#ifndef __SSE2_MATH__
# define libc_feholdexcept_setround_53bit libc_feholdexcept_setround_387_53bit
# define libc_feholdsetround_53bit libc_feholdsetround_387_53bit
#endif
/* We have support for rounding mode context. */
#define HAVE_RM_CTX 1
static __always_inline void
libc_feholdexcept_setround_sse_ctx (struct rm_ctx *ctx, int r)
{
unsigned int mxcsr, new_mxcsr;
asm (STMXCSR " %0" : "=m" (*&mxcsr));
new_mxcsr = ((mxcsr | 0x1f80) & ~0x603f) | (r << 3);
ctx->env.__mxcsr = mxcsr;
if (__glibc_unlikely (mxcsr != new_mxcsr))
{
asm volatile (LDMXCSR " %0" : : "m" (*&new_mxcsr));
ctx->updated_status = true;
}
else
ctx->updated_status = false;
}
/* Unconditional since we want to overwrite any exceptions that occurred in the
context. This is also why all fehold* functions unconditionally write into
ctx->env. */
static __always_inline void
libc_fesetenv_sse_ctx (struct rm_ctx *ctx)
{
libc_fesetenv_sse (&ctx->env);
}
static __always_inline void
libc_feupdateenv_sse_ctx (struct rm_ctx *ctx)
{
if (__glibc_unlikely (ctx->updated_status))
libc_feupdateenv_test_sse (&ctx->env, 0);
}
static __always_inline void
libc_feholdexcept_setround_387_prec_ctx (struct rm_ctx *ctx, int r)
{
libc_feholdexcept_387 (&ctx->env);
fpu_control_t cw = ctx->env.__control_word;
fpu_control_t old_cw = cw;
cw &= ~(_FPU_RC_ZERO | _FPU_EXTENDED);
cw |= r | 0x3f;
if (__glibc_unlikely (old_cw != cw))
{
_FPU_SETCW (cw);
ctx->updated_status = true;
}
else
ctx->updated_status = false;
}
static __always_inline void
libc_feholdexcept_setround_387_ctx (struct rm_ctx *ctx, int r)
{
libc_feholdexcept_setround_387_prec_ctx (ctx, r | _FPU_EXTENDED);
}
static __always_inline void
libc_feholdexcept_setround_387_53bit_ctx (struct rm_ctx *ctx, int r)
{
libc_feholdexcept_setround_387_prec_ctx (ctx, r | _FPU_DOUBLE);
}
static __always_inline void
libc_feholdsetround_387_prec_ctx (struct rm_ctx *ctx, int r)
{
fpu_control_t cw, new_cw;
_FPU_GETCW (cw);
new_cw = cw;
new_cw &= ~(_FPU_RC_ZERO | _FPU_EXTENDED);
new_cw |= r;
ctx->env.__control_word = cw;
if (__glibc_unlikely (new_cw != cw))
{
_FPU_SETCW (new_cw);
ctx->updated_status = true;
}
else
ctx->updated_status = false;
}
static __always_inline void
libc_feholdsetround_387_ctx (struct rm_ctx *ctx, int r)
{
libc_feholdsetround_387_prec_ctx (ctx, r | _FPU_EXTENDED);
}
static __always_inline void
libc_feholdsetround_387_53bit_ctx (struct rm_ctx *ctx, int r)
{
libc_feholdsetround_387_prec_ctx (ctx, r | _FPU_DOUBLE);
}
static __always_inline void
libc_feholdsetround_sse_ctx (struct rm_ctx *ctx, int r)
{
unsigned int mxcsr, new_mxcsr;
asm (STMXCSR " %0" : "=m" (*&mxcsr));
new_mxcsr = (mxcsr & ~0x6000) | (r << 3);
ctx->env.__mxcsr = mxcsr;
if (__glibc_unlikely (new_mxcsr != mxcsr))
{
asm volatile (LDMXCSR " %0" : : "m" (*&new_mxcsr));
ctx->updated_status = true;
}
else
ctx->updated_status = false;
}
static __always_inline void
libc_feresetround_sse_ctx (struct rm_ctx *ctx)
{
if (__glibc_unlikely (ctx->updated_status))
libc_feresetround_sse (&ctx->env);
}
static __always_inline void
libc_feresetround_387_ctx (struct rm_ctx *ctx)
{
if (__glibc_unlikely (ctx->updated_status))
_FPU_SETCW (ctx->env.__control_word);
}
static __always_inline void
libc_feupdateenv_387_ctx (struct rm_ctx *ctx)
{
if (__glibc_unlikely (ctx->updated_status))
libc_feupdateenv_test_387 (&ctx->env, 0);
}
#ifdef __SSE_MATH__
# define libc_feholdexcept_setroundf_ctx libc_feholdexcept_setround_sse_ctx
# define libc_fesetenvf_ctx libc_fesetenv_sse_ctx
# define libc_feupdateenvf_ctx libc_feupdateenv_sse_ctx
# define libc_feholdsetroundf_ctx libc_feholdsetround_sse_ctx
# define libc_feresetroundf_ctx libc_feresetround_sse_ctx
#else
# define libc_feholdexcept_setroundf_ctx libc_feholdexcept_setround_387_ctx
# define libc_feupdateenvf_ctx libc_feupdateenv_387_ctx
# define libc_feholdsetroundf_ctx libc_feholdsetround_387_ctx
# define libc_feresetroundf_ctx libc_feresetround_387_ctx
#endif /* __SSE_MATH__ */
#ifdef __SSE2_MATH__
# define libc_feholdexcept_setround_ctx libc_feholdexcept_setround_sse_ctx
# define libc_fesetenv_ctx libc_fesetenv_sse_ctx
# define libc_feupdateenv_ctx libc_feupdateenv_sse_ctx
# define libc_feholdsetround_ctx libc_feholdsetround_sse_ctx
# define libc_feresetround_ctx libc_feresetround_sse_ctx
#else
# define libc_feholdexcept_setround_ctx libc_feholdexcept_setround_387_ctx
# define libc_feupdateenv_ctx libc_feupdateenv_387_ctx
# define libc_feresetround_ctx libc_feresetround_387_ctx
#endif /* __SSE2_MATH__ */
#define libc_feholdexcept_setroundl_ctx libc_feholdexcept_setround_387_ctx
#define libc_feupdateenvl_ctx libc_feupdateenv_387_ctx
#define libc_feholdsetroundl_ctx libc_feholdsetround_387_ctx
#define libc_feresetroundl_ctx libc_feresetround_387_ctx
#ifndef __SSE2_MATH__
# define libc_feholdsetround_53bit_ctx libc_feholdsetround_387_53bit_ctx
# define libc_feresetround_53bit_ctx libc_feresetround_387_ctx
#endif
#undef __mxcsr
#endif /* FENV_PRIVATE_H */
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