DebugInfo: Move DILocation::computeNewDiscriminators()

As documented in PR23200 (and the FIXMEs I've added to the code here),
this logic is fairly broken: it modifies the `LLVMContext` in a way that
affects other modules and cannot be serialized to assembly/bitcode.  For
now, move it over to `MDLocation::computeNewDiscriminators()` anyway.

llvm-svn: 234825
diff --git a/llvm/lib/Transforms/Utils/AddDiscriminators.cpp b/llvm/lib/Transforms/Utils/AddDiscriminators.cpp
index 4197e35..2cbe93e 100644
--- a/llvm/lib/Transforms/Utils/AddDiscriminators.cpp
+++ b/llvm/lib/Transforms/Utils/AddDiscriminators.cpp
@@ -195,7 +195,13 @@
         StringRef Filename = FirstDIL.getFilename();
         DIScope Scope = FirstDIL.getScope();
         DIFile File = Builder.createFile(Filename, Scope.getDirectory());
-        unsigned Discriminator = FirstDIL.computeNewDiscriminator(Ctx);
+
+        // FIXME: Calculate the discriminator here, based on local information,
+        // and delete MDLocation::computeNewDiscriminator().  The current
+        // solution gives different results depending on other modules in the
+        // same context.  All we really need is to discriminate between
+        // FirstDIL and LastDIL -- a local map would suffice.
+        unsigned Discriminator = FirstDIL->computeNewDiscriminator();
         DILexicalBlockFile NewScope =
             Builder.createLexicalBlockFile(Scope, File, Discriminator);
         DILocation NewDIL =