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, 4 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/LiveDebugVariables.cpp b/llvm/lib/CodeGen/LiveDebugVariables.cpp
index 2e8615219c8..a07a7c9e567 100644
--- a/llvm/lib/CodeGen/LiveDebugVariables.cpp
+++ b/llvm/lib/CodeGen/LiveDebugVariables.cpp
@@ -378,12 +378,13 @@ static void printDebugLoc(DebugLoc DL, raw_ostream &CommentOS,
   CommentOS << " ]";
 }
 
-static void printExtendedName(raw_ostream &OS, const MDLocalVariable *V) {
+static void printExtendedName(raw_ostream &OS, const MDLocalVariable *V,
+                              const MDLocation *DL) {
   const LLVMContext &Ctx = V->getContext();
   StringRef Res = V->getName();
   if (!Res.empty())
     OS << Res << "," << V->getLine();
-  if (auto *InlinedAt = V->getInlinedAt()) {
+  if (auto *InlinedAt = DL->getInlinedAt()) {
     if (DebugLoc InlinedAtDL = InlinedAt) {
       OS << " @[";
       printDebugLoc(InlinedAtDL, OS, Ctx);
@@ -395,7 +396,7 @@ static void printExtendedName(raw_ostream &OS, const MDLocalVariable *V) {
 void UserValue::print(raw_ostream &OS, const TargetRegisterInfo *TRI) {
   DIVariable DV = cast<MDLocalVariable>(Variable);
   OS << "!\"";
-  printExtendedName(OS, DV);
+  printExtendedName(OS, DV, dl);
 
   OS << "\"\t";
   if (offset)