gold plugin: create internal replacement with original linkage first.

The call to copyAttributesFrom will copy the visibility, which might assert
if it were to produce something invalid like "internal hidden". We avoid it
by first creating the replacement with the original linkage and then setting
it to internal affter the call to copyAttributesFrom.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219184 91177308-0d34-0410-b5e6-96231b3b80d8
[FastISel][AArch64] Fix "Fold sign-/zero-extends into the load instruction."

This commit fixes an issue with sign-/zero-extending loads that was discovered
by Richard Barton.

We use now the correct load instructions for sign-extending loads to 64bit. Also
updated and added more unit tests.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219185 91177308-0d34-0410-b5e6-96231b3b80d8
[FastISel][AArch64] Teach the address computation to also fold sub instructions.

Tiny enhancement to the address computation code to also fold sub instructions
if the rhs is constant and can be folded into the offset.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219186 91177308-0d34-0410-b5e6-96231b3b80d8
[FastISel][AArch64] Teach the address computation code to also fold sign-/zero-extends.

The code already folds sign-/zero-extends, but only if they are arguments to
mul and shift instructions. This extends the code to also fold them when they
are direct inputs.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219187 91177308-0d34-0410-b5e6-96231b3b80d8
gold plugin: Handle gold selecting a linkonce GV when a weak is present.

The plugin API doesn't have the notion of linkonce, only weak. It is up to the
plugin to figure out if a symbol used only for the symbol table can be dropped.
In particular, it has to avoid dropping a linkonce_odr selected by gold if there
is also a weak_odr.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219188 91177308-0d34-0410-b5e6-96231b3b80d8