diff mbox

[i386] : Use reciprocal sequences for vectorized SFmode division and sqrtf(x) for -ffast-math

Message ID CAFULd4Y=8G+AZ0Xdmh9Voa=JNc=F+qGP=UoF2y4GhMEXxWhe=A@mail.gmail.com
State New
Headers show

Commit Message

Uros Bizjak Oct. 20, 2011, 3:17 p.m. UTC 
On Thu, Oct 20, 2011 at 4:45 PM, Joseph S. Myers
<joseph@codesourcery.com> wrote:

>> The patch was tested on x86_64-pc-linux-gnu, but I would like Joseph
>> to check if I didn't mess something with options handling.
>
> I have no comments on the option handling in this patch.
>
>> +for vectorized single float division and vectorized sqrtf(x) already with
>
> @code{sqrtf (@var{x})}

Thanks - fixed, with a similar fix in the previous paragraph.

I also found a PR that deals with vectorized reciprocal, so I referred
to the PR in the ChangeLog entry:

2011-10-20  Uros Bizjak  <ubizjak@gmail.com>

	PR target/47989
	* config/i386/i386.h (RECIP_MASK_DEFAULT): New define.
	* config/i386/i386.op (recip_mask): Initialize with RECIP_MASK_DEFAULT.
	* doc/invoke.texi (ix86 Options, -mrecip): Document that GCC
	implements vectorized single float division and vectorized sqrtf(x)
	with reciprocal sequence with additional Newton-Raphson step with
	-ffast-math.

Attached is the patch that was committed to mainline SVN. Encouraged
by Michael's results, let's see what automated benchmark testers will
show.

Uros.
diff mbox

Patch

Index: config/i386/i386.h
===================================================================
--- config/i386/i386.h	(revision 180255)
+++ config/i386/i386.h	(working copy)
@@ -2322,6 +2322,7 @@ 
 #define RECIP_MASK_VEC_SQRT	0x08
 #define RECIP_MASK_ALL	(RECIP_MASK_DIV | RECIP_MASK_SQRT \
 			 | RECIP_MASK_VEC_DIV | RECIP_MASK_VEC_SQRT)
+#define RECIP_MASK_DEFAULT (RECIP_MASK_VEC_DIV | RECIP_MASK_VEC_SQRT)
 
 #define TARGET_RECIP_DIV	((recip_mask & RECIP_MASK_DIV) != 0)
 #define TARGET_RECIP_SQRT	((recip_mask & RECIP_MASK_SQRT) != 0)
Index: config/i386/i386.opt
===================================================================
--- config/i386/i386.opt	(revision 180255)
+++ config/i386/i386.opt	(working copy)
@@ -32,7 +32,7 @@ 
 HOST_WIDE_INT ix86_isa_flags_explicit
 
 TargetVariable
-int recip_mask
+int recip_mask = RECIP_MASK_DEFAULT
 
 Variable
 int recip_mask_explicit
Index: doc/invoke.texi
===================================================================
--- doc/invoke.texi	(revision 180255)
+++ doc/invoke.texi	(working copy)
@@ -12922,7 +12922,12 @@ 
 of the non-reciprocal instruction, the precision of the sequence can be
 decreased by up to 2 ulp (i.e. the inverse of 1.0 equals 0.99999994).
 
-Note that GCC implements 1.0f/sqrtf(x) in terms of RSQRTSS (or RSQRTPS)
+Note that GCC implements @code{1.0f/sqrtf(@var{x})} in terms of RSQRTSS
+(or RSQRTPS) already with @option{-ffast-math} (or the above option
+combination), and doesn't need @option{-mrecip}.
+
+Also note that GCC emits the above sequence with additional Newton-Raphson step
+for vectorized single float division and vectorized @code{sqrtf(@var{x})}
 already with @option{-ffast-math} (or the above option combination), and
 doesn't need @option{-mrecip}.