[llgo] Roll gofrontend forward

Switch gofrontend to using go.googlesource.com, and
update to 81eb6a3f425b2158c67ee32c0cc973a72ce9d6be.

There are various changes required to update to the
go 1.5 runtime:

typemap.go is changed to accommodate the change in representation for equal/hash algorithms, and the removal of the zero value/type.
CMakeLists.txt is updated to add the build tree to the package search path, so internal packages, which are not installed, are found.
various files changes due to removal of __go_new_nopointers; the same change as in D11863, but with NoUnwindAttribute added to the added runtime functions which are called with "callOnly".
minor cleanups in ssa.go while investigating issues with unwinding/panic handling.

Differential Revisision: http://reviews.llvm.org/D15188

llvm-svn: 263536

1 files changed, 6 insertions, 0 deletions

diff --git a/llgo/third_party/gofrontend/libgo/go/math/sqrt.go b/llgo/third_party/gofrontend/libgo/go/math/sqrt.go
index 56122b59814..215d6485442 100644
--- a/llgo/third_party/gofrontend/libgo/go/math/sqrt.go
+++ b/llgo/third_party/gofrontend/libgo/go/math/sqrt.go
@@ -96,6 +96,12 @@ func Sqrt(x float64) float64 {
 //	Sqrt(±0) = ±0
 //	Sqrt(x < 0) = NaN
 //	Sqrt(NaN) = NaN
+
+// Note: Sqrt is implemented in assembly on some systems.
+// Others have assembly stubs that jump to func sqrt below.
+// On systems where Sqrt is a single instruction, the compiler
+// may turn a direct call into a direct use of that instruction instead.
+
 func sqrt(x float64) float64 {
 	// special cases
 	switch {