cmd/internal/gc: use hardware instruction for math.Sqrt (amd64/arm)
I first prototyped this change in Sept 2011, and I discarded it
because it made no difference in the obvious benchmark loop.
It still makes no difference in the obvious benchmark loop,
but in a less obvious one, doing some extra computation
around the calls to Sqrt, not making the call does have a
significant effect.
benchmark old ns/op new ns/op delta
BenchmarkSqrt 4.56 4.57 +0.22%
BenchmarkSqrtIndirect 4.56 4.56 +0.00%
BenchmarkSqrtGo 69.4 69.4 +0.00%
BenchmarkSqrtPrime 4417 3647 -17.43%
This is a warmup for using hardware expansions for some
calls to 1-line assembly routines in the runtime (for example getg).
Change-Id: Ie66be23f8c09d0f7dc4ddd7ca8a93cfce28f55a4
Reviewed-on: https://go-review.googlesource.com/8356
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
diff --git a/src/cmd/internal/gc/cgen.go b/src/cmd/internal/gc/cgen.go
index b3524c2..d3921f7 100644
--- a/src/cmd/internal/gc/cgen.go
+++ b/src/cmd/internal/gc/cgen.go
@@ -409,6 +409,15 @@
cgen_norm(n, &n1, res)
return
+ case OSQRT:
+ var n1 Node
+ Regalloc(&n1, nl.Type, res)
+ Cgen(n.Left, &n1)
+ Thearch.Gins(Thearch.Optoas(OSQRT, nl.Type), &n1, &n1)
+ Thearch.Gmove(&n1, res)
+ Regfree(&n1)
+ return
+
// symmetric binary
case OAND,
OOR,
