[PPC] Use alias symbols in address computation.

This seems to match what gcc does for ppc and what every other llvm
backend does.

This is a fixed version of r209638. The difference is to avoid any change
in behavior for functions. The logic for using constant pools for function
addresseses is spread over a few places and we have to keep them in sync.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209821 91177308-0d34-0410-b5e6-96231b3b80d8

test/CodeGen/PowerPC/alias.ll

@@ -0,0 +1,31 @@
+; RUN: llc < %s -mtriple=powerpc64-unknown-linux-gnu -code-model=medium| FileCheck --check-prefix=CHECK --check-prefix=MEDIUM %s
+; RUN: llc < %s -mtriple=powerpc64-unknown-linux-gnu -code-model=large | FileCheck --check-prefix=CHECK --check-prefix=LARGE %s
+
+@foo = global i32 42
+@fooa = alias i32* @foo
+
+@foo2 = global i64 42
+@foo2a = alias i64* @foo2
+
+; CHECK-LABEL: bar:
+define i32 @bar() {
+; MEDIUM: addis 3, 2, fooa@toc@ha
+; LARGE: addis 3, 2, .LC1@toc@ha
+  %a = load i32* @fooa
+  ret i32 %a
+}
+
+; CHECK-LABEL: bar2:
+define i64 @bar2() {
+; MEDIUM: addis 3, 2, foo2a@toc@ha
+; MEDIUM: addi 3, 3, foo2a@toc@l
+; LARGE: addis 3, 2, .LC3@toc@ha
+  %a = load i64* @foo2a
+  ret i64 %a
+}
+
+; LARGE: .LC1:
+; LARGE-NEXT: .tc fooa[TC],fooa
+
+; LARGE: .LC3:
+; LARGE-NEXT: .tc foo2a[TC],foo2a