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PowerPC: remove branch prediction from rint implementation

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The branch prediction hints is actually hurts performance in this case.
The assembly implementation make two assumptions: 1. 'fabs (x) < 2^52'
is unlikely and 2. 'x > 0.0' is unlike (if 1. is true). Since it a
general floating point function, expected input is not bounded and then
it is better to let the hardware handle the branches.
This commit is contained in:
Adhemerval Zanella 2013-03-29 18:15:28 -05:00
parent 6142896d53
commit 60c414c346
6 changed files with 22 additions and 13 deletions
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7
benchtests/Makefile
View File

@ -43,7 +43,7 @@
# See pow-inputs for an example.
subdir := benchtests
bench := exp pow
bench := exp pow rint
exp-ITER = 100000
exp-ARGLIST = double
@ -55,5 +55,10 @@ pow-ARGLIST = double:double
pow-RET = double
LDFLAGS-bench-pow = -lm
rint-ITER = 250000000
rint-ARGLIST = double
rint-RET = double
LDFLAGS-bench-rint = -lm
include ../Makeconfig
include ../Rules

4
benchtests/rint-inputs Normal file
View File

@ -0,0 +1,4 @@
78.5
-78.5
4503599627370497.0
-4503599627370497.0

6
sysdeps/powerpc/powerpc32/fpu/s_rint.S
View File

@ -45,14 +45,14 @@ ENTRY (__rint)
fsub fp12,fp13,fp13 /* generate 0.0 */
fcmpu cr7,fp0,fp13 /* if (fabs(x) > TWO52) */
fcmpu cr6,fp1,fp12 /* if (x > 0.0) */
bnllr- cr7
bng- cr6,.L4
bnllr cr7
bng cr6,.L4
fadd fp1,fp1,fp13 /* x+= TWO52; */
fsub fp1,fp1,fp13 /* x-= TWO52; */
fabs fp1,fp1 /* if (x == 0.0) */
blr /* x = 0.0; */
.L4:
bnllr- cr6 /* if (x < 0.0) */
bnllr cr6 /* if (x < 0.0) */
fsub fp1,fp1,fp13 /* x-= TWO52; */
fadd fp1,fp1,fp13 /* x+= TWO52; */
fnabs fp1,fp1 /* if (x == 0.0) */

6
sysdeps/powerpc/powerpc32/fpu/s_rintf.S
View File

@ -41,14 +41,14 @@ ENTRY (__rintf)
fsubs fp12,fp13,fp13 /* generate 0.0 */
fcmpu cr7,fp0,fp13 /* if (fabs(x) > TWO23) */
fcmpu cr6,fp1,fp12 /* if (x > 0.0) */
bnllr- cr7
bng- cr6,.L4
bnllr cr7
bng cr6,.L4
fadds fp1,fp1,fp13 /* x+= TWO23; */
fsubs fp1,fp1,fp13 /* x-= TWO23; */
fabs fp1,fp1 /* if (x == 0.0) */
blr /* x = 0.0; */
.L4:
bnllr- cr6 /* if (x < 0.0) */
bnllr cr6 /* if (x < 0.0) */
fsubs fp1,fp1,fp13 /* x-= TWO23; */
fadds fp1,fp1,fp13 /* x+= TWO23; */
fnabs fp1,fp1 /* if (x == 0.0) */

6
sysdeps/powerpc/powerpc64/fpu/s_rint.S
View File

@ -34,14 +34,14 @@ EALIGN (__rint, 4, 0)
fsub fp12,fp13,fp13 /* generate 0.0 */
fcmpu cr7,fp0,fp13 /* if (fabs(x) > TWO52) */
fcmpu cr6,fp1,fp12 /* if (x > 0.0) */
bnllr- cr7
bng- cr6,.L4
bnllr cr7
bng cr6,.L4
fadd fp1,fp1,fp13 /* x+= TWO52; */
fsub fp1,fp1,fp13 /* x-= TWO52; */
fabs fp1,fp1 /* if (x == 0.0) */
blr /* x = 0.0; */
.L4:
bnllr- cr6 /* if (x < 0.0) */
bnllr cr6 /* if (x < 0.0) */
fsub fp1,fp1,fp13 /* x-= TWO52; */
fadd fp1,fp1,fp13 /* x+= TWO52; */
fnabs fp1,fp1 /* if (x == 0.0) */

6
sysdeps/powerpc/powerpc64/fpu/s_rintf.S
View File

@ -30,14 +30,14 @@ EALIGN (__rintf, 4, 0)
fsubs fp12,fp13,fp13 /* generate 0.0 */
fcmpu cr7,fp0,fp13 /* if (fabs(x) > TWO23) */
fcmpu cr6,fp1,fp12 /* if (x > 0.0) */
bnllr- cr7
bng- cr6,.L4
bnllr cr7
bng cr6,.L4
fadds fp1,fp1,fp13 /* x+= TWO23; */
fsubs fp1,fp1,fp13 /* x-= TWO23; */
fabs fp1,fp1 /* if (x == 0.0) */
blr /* x = 0.0; */
.L4:
bnllr- cr6 /* if (x < 0.0) */
bnllr cr6 /* if (x < 0.0) */
fsubs fp1,fp1,fp13 /* x-= TWO23; */
fadds fp1,fp1,fp13 /* x+= TWO23; */
fnabs fp1,fp1 /* if (x == 0.0) */