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, 3 insertions, 2 deletions

diff --git a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
index bd4d70b25aa..6caec344d1f 100644
--- a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
+++ b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -1911,7 +1911,8 @@ std::error_code BitcodeReader::ParseMetadata() {
       break;
     }
     case bitc::METADATA_LOCAL_VAR: {
-      if (Record.size() != 10)
+      // 10th field is for the obseleted 'inlinedAt:' field.
+      if (Record.size() != 9 && Record.size() != 10)
         return Error("Invalid record");
 
       MDValueList.AssignValue(
@@ -1919,7 +1920,7 @@ std::error_code BitcodeReader::ParseMetadata() {
                           (Context, Record[1], getMDOrNull(Record[2]),
                            getMDString(Record[3]), getMDOrNull(Record[4]),
                            Record[5], getMDOrNull(Record[6]), Record[7],
-                           Record[8], getMDOrNull(Record[9]))),
+                           Record[8])),
           NextMDValueNo++);
       break;
     }