DebugInfo: Rewrite atSameLineAs() as MDLocation::canDiscriminate()

Rewrite `DILocation::atSameLineAs()` as `MDLocation::canDiscriminate()`
with a doxygen comment explaining its purpose.  I've added a few FIXMEs
where I think this check is too weak; fixing that is tracked by PR23199.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@234674 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/IR/DebugInfo.h

@@ -810,10 +810,7 @@ public:
   }
   StringRef getFilename() const { return get()->getFilename(); }
   StringRef getDirectory() const { return get()->getDirectory(); }
-  bool atSameLineAs(const DILocation &Other) const {
-    return (getLineNumber() == Other.getLineNumber() &&
-            getFilename() == Other.getFilename());
-  }
+
   /// \brief Get the DWAF discriminator.
   ///
   /// DWARF discriminators are used to distinguish identical file locations for

include/llvm/IR/DebugInfoMetadata.h

@@ -1166,6 +1166,23 @@ public:
     return getScope();
   }
 
+  /// \brief Check whether this can be discriminated from another location.
+  ///
+  /// Check \c this can be discriminated from \c RHS in a linetable entry.
+  /// Scope and inlined-at chains are not recorded in the linetable, so they
+  /// cannot be used to distinguish basic blocks.
+  ///
+  /// The current implementation is weaker than it should be, since it just
+  /// checks filename and line.
+  ///
+  /// FIXME: Add a check for getDiscriminator().
+  /// FIXME: Add a check for getColumn().
+  /// FIXME: Change the getFilename() check to getFile() (or add one for
+  /// getDirectory()).
+  bool canDiscriminate(const MDLocation &RHS) const {
+    return getFilename() != RHS.getFilename() || getLine() != RHS.getLine();
+  }
+
   Metadata *getRawScope() const { return getOperand(0); }
   Metadata *getRawInlinedAt() const {
     if (getNumOperands() == 2)

lib/Transforms/Utils/AddDiscriminators.cpp

@@ -189,7 +189,7 @@ bool AddDiscriminators::runOnFunction(Function &F) {
       // location as B's last instruction (Last), add a new
       // discriminator for First's location and all the instructions
       // in Succ that share the same location with First.
-      if (FirstDIL.atSameLineAs(LastDIL)) {
+      if (!FirstDIL->canDiscriminate(*LastDIL)) {
         // Create a new lexical scope and compute a new discriminator
         // number for it.
         StringRef Filename = FirstDIL.getFilename();