Implement -fsemantic-interposition
First attempt at implementing -fsemantic-interposition.
Rely on GlobalValue::isInterposable that already captures most of the expected
behavior.
Rely on a ModuleFlag to state whether we should respect SemanticInterposition or
not. The default remains no.
So this should be a no-op if -fsemantic-interposition isn't used, and if it is,
isInterposable being already used in most optimisation, they should honor it
properly.
Note that it only impacts architecture compiled with -fPIC and no pie.
Differential Revision: https://reviews.llvm.org/D72829
diff --git a/clang/test/CodeGen/semantic-interposition.c b/clang/test/CodeGen/semantic-interposition.c
new file mode 100644
index 0000000..77df615
--- /dev/null
+++ b/clang/test/CodeGen/semantic-interposition.c
@@ -0,0 +1,14 @@
+// Semantic Interposition is active if
+// -fsemantic-interposition is set,
+// - pic-level > 0
+// - pic-is-pie is not set
+
+// RUN: %clang_cc1 -emit-llvm -fsemantic-interposition -pic-level 0 %s -o - | FileCheck %s -check-prefix=CHECK-NO-INTERPOSITION
+// RUN: %clang_cc1 -emit-llvm -fsemantic-interposition -pic-level 1 %s -o - | FileCheck %s -check-prefix=CHECK-INTERPOSITION
+// RUN: %clang_cc1 -emit-llvm -fsemantic-interposition -pic-level 2 %s -o - | FileCheck %s -check-prefix=CHECK-INTERPOSITION
+// RUN: %clang_cc1 -emit-llvm -fsemantic-interposition -pic-level 0 %s -o - | FileCheck %s -check-prefix=CHECK-NO-INTERPOSITION
+// RUN: %clang_cc1 -emit-llvm -fsemantic-interposition -pic-level 1 -pic-is-pie %s -o - | FileCheck %s -check-prefix=CHECK-NO-INTERPOSITION
+// RUN: %clang_cc1 -emit-llvm -fsemantic-interposition -pic-level 2 -pic-is-pie %s -o - | FileCheck %s -check-prefix=CHECK-NO-INTERPOSITION
+
+// CHECK-NO-INTERPOSITION-NOT: "SemanticInterposition"
+// CHECK-INTERPOSITION: !{{[0-9]+}} = !{i32 1, !"SemanticInterposition", i32 1}