DebugInfo: Remove 'inlinedAt:' field from MDLocalVariable

Remove 'inlinedAt:' from MDLocalVariable.  Besides saving some memory
(variables with it seem to be single largest `Metadata` contributer to
memory usage right now in -g -flto builds), this stops optimization and
backend passes from having to change local variables.

The 'inlinedAt:' field was used by the backend in two ways:

 1. To tell the backend whether and into what a variable was inlined.
 2. To create a unique id for each inlined variable.

Instead, rely on the 'inlinedAt:' field of the intrinsic's `!dbg`
attachment, and change the DWARF backend to use a typedef called
`InlinedVariable` which is `std::pair<MDLocalVariable*, MDLocation*>`.
This `DebugLoc` is already passed reliably through the backend (as
verified by r234021).

This commit removes the check from r234021, but I added a new check
(that will survive) in r235048, and changed the `DIBuilder` API in
r235041 to require a `!dbg` attachment whose 'scope:` is in the same
`MDSubprogram` as the variable's.

If this breaks your out-of-tree testcases, perhaps the script I used
(mdlocalvariable-drop-inlinedat.sh) will help; I'll attach it to PR22778
in a moment.

llvm-svn: 235050

1 files changed, 9 insertions, 5 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/DbgValueHistoryCalculator.h b/llvm/lib/CodeGen/AsmPrinter/DbgValueHistoryCalculator.h
index 4b6200717d2..c25aaffd2d1 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DbgValueHistoryCalculator.h
+++ b/llvm/lib/CodeGen/AsmPrinter/DbgValueHistoryCalculator.h
@@ -17,7 +17,8 @@ namespace llvm {
 
 class MachineFunction;
 class MachineInstr;
-class MDNode;
+class MDLocalVariable;
+class MDLocation;
 class TargetRegisterInfo;
 
 // For each user variable, keep a list of instruction ranges where this variable
@@ -31,16 +32,19 @@ class DbgValueHistoryMap {
 public:
   typedef std::pair<const MachineInstr *, const MachineInstr *> InstrRange;
   typedef SmallVector<InstrRange, 4> InstrRanges;
-  typedef MapVector<const MDNode *, InstrRanges> InstrRangesMap;
+  typedef std::pair<const MDLocalVariable *, const MDLocation *>
+      InlinedVariable;
+  typedef MapVector<InlinedVariable, InstrRanges> InstrRangesMap;
+
 private:
   InstrRangesMap VarInstrRanges;
 
 public:
-  void startInstrRange(const MDNode *Var, const MachineInstr &MI);
-  void endInstrRange(const MDNode *Var, const MachineInstr &MI);
+  void startInstrRange(InlinedVariable Var, const MachineInstr &MI);
+  void endInstrRange(InlinedVariable Var, const MachineInstr &MI);
   // Returns register currently describing @Var. If @Var is currently
   // unaccessible or is not described by a register, returns 0.
-  unsigned getRegisterForVar(const MDNode *Var) const;
+  unsigned getRegisterForVar(InlinedVariable Var) const;
 
   bool empty() const { return VarInstrRanges.empty(); }
   void clear() { VarInstrRanges.clear(); }