On Mon, Feb 22, 2016 at 06:50:44PM -0600, Evandro Menezes wrote:
In preparation for the patch adding the Newton series also for
square root, I'd like to propose this patch changing the name of the
existing tuning flag for the reciprocal square root.
This is fine, other names like sw_rsqrt, expand_rsqrt, nr_rsqrt would also
be OK. Pick your favourite!
One comment on the replacement invoke.texi text below, otherwise this is
OK to apply now.
diff --git a/gcc/config/aarch64/aarch64.opt b/gcc/config/aarch64/aarch64.opt
index 5cbd4cd..155d2bd 100644
--- a/gcc/config/aarch64/aarch64.opt
+++ b/gcc/config/aarch64/aarch64.opt
@@ -151,5 +151,5 @@ PC relative literal loads.
mlow-precision-recip-sqrt
Common Var(flag_mrecip_low_precision_sqrt) Optimization
-When calculating a sqrt approximation, run fewer steps.
+Calculate the reciprocal square-root approximation in fewer steps.
This reduces precision, but can result in faster computation.
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 490df93..eeff24d 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -12879,12 +12879,10 @@ corresponding flag to the linker.
@item -mno-low-precision-recip-sqrt
@opindex -mlow-precision-recip-sqrt
@opindex -mno-low-precision-recip-sqrt
-The square root estimate uses two steps instead of three for double-precision,
-and one step instead of two for single-precision.
-Thus reducing latency and precision.
-This is only relevant if @option{-ffast-math} activates
-reciprocal square root estimate instructions.
-Which in turn depends on the target processor.
+The reciprocal square root approximation uses one step less than otherwise,
+thus reducing latency and precision.
When calculating the reciprocal square root approximation, use one less
step than otherwise, thus reducing latency and precision.