[Hexagon] New HVX target features.

This patch lets the llvm tools handle the new HVX target features that
are added by frontend (clang). The target-features are of the form
"hvx-length64b" for 64 Byte HVX mode, "hvx-length128b" for 128 Byte mode HVX.
"hvx-double" is an alias to "hvx-length128b" and is soon will be deprecated.
The hvx version target feature is upgated form "+hvx" to "+hvxv{version_number}.
Eg: "+hvxv62"

For the correct HVX code generation, the user must use the following
target features.
For 64B mode: "+hvxv62" "+hvx-length64b"
For 128B mode: "+hvxv62" "+hvx-length128b"

Clang picks a default length if none is specified. If for some reason,
no hvx-length is specified to llvm, the compilation will bail out.
There is a corresponding clang patch.

Differential Revision: https://reviews.llvm.org/D38851

llvm-svn: 316101
diff --git a/llvm/test/CodeGen/Hexagon/multi-cycle.ll b/llvm/test/CodeGen/Hexagon/multi-cycle.ll
index fc02182..b8caef9 100644
--- a/llvm/test/CodeGen/Hexagon/multi-cycle.ll
+++ b/llvm/test/CodeGen/Hexagon/multi-cycle.ll
@@ -95,7 +95,7 @@
 declare <16 x i32> @llvm.hexagon.V6.vabsdiffh(<16 x i32>, <16 x i32>) #1
 declare <16 x i32> @llvm.hexagon.V6.vabsh(<16 x i32>) #1
 
-attributes #0 = { nounwind "target-cpu"="hexagonv60" "target-features"="+hvx" }
+attributes #0 = { nounwind "target-cpu"="hexagonv60" "target-features"="+hvxv60,+hvx-length64b" }
 attributes #1 = { nounwind readnone }
 
 !1 = !{!2, !2, i64 0}