Linker: Add flag to override linkage rules

Add a flag to lib/Linker (and `llvm-link`) to override linkage rules.
When set, the functions in the source module *always* replace those in
the destination module.

The `llvm-link` option is `-override=abc.ll`.  All the "regular" modules
are loaded and linked first, followed by the `-override` modules.  This
is useful for debugging workflows where some subset of the module (e.g.,
a single function) is extracted into a separate file where it's
optimized differently, before being merged back in.

Patch by Luqman Aden!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@235473 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 23 insertions, 0 deletions

diff --git a/test/Linker/override-with-internal-linkage-2.ll b/test/Linker/override-with-internal-linkage-2.ll
new file mode 100644
index 00000000000..2de52a925b2
--- /dev/null
+++ b/test/Linker/override-with-internal-linkage-2.ll
@@ -0,0 +1,23 @@
+; RUN: llvm-link %s -override %S/Inputs/override-with-internal-linkage-2.ll -S | FileCheck %s
+; RUN: llvm-link -override %S/Inputs/override-with-internal-linkage-2.ll %s -S | FileCheck %s
+
+; CHECK-LABEL: define i32 @foo
+; CHECK-NEXT: entry:
+; CHECK-NEXT: %add = add nsw i32 %i, %i
+; CHECK-NEXT: ret i32 %add
+define i32 @foo(i32 %i) {
+entry:
+  %add = add nsw i32 %i, %i
+  ret i32 %add
+}
+
+; CHECK-LABEL: define internal i32 @foo1
+; CHECK-NEXT: entry:
+; CHECK-NEXT: ret i32 4
+
+; Function Attrs: nounwind ssp uwtable
+define i32 @main(i32 %argc, i8** %argv) {
+entry:
+  %a = call i32 @foo(i32 2)
+  ret i32 %a
+}