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, 5 insertions, 7 deletions

diff --git a/llvm/lib/AsmParser/LLParser.cpp b/llvm/lib/AsmParser/LLParser.cpp
index 1cd1c795eae..64ed2a2b7e3 100644
--- a/llvm/lib/AsmParser/LLParser.cpp
+++ b/llvm/lib/AsmParser/LLParser.cpp
@@ -3680,8 +3680,7 @@ bool LLParser::ParseMDGlobalVariable(MDNode *&Result, bool IsDistinct) {
 
 /// ParseMDLocalVariable:
 ///   ::= !MDLocalVariable(tag: DW_TAG_arg_variable, scope: !0, name: "foo",
-///                        file: !1, line: 7, type: !2, arg: 2, flags: 7,
-///                        inlinedAt: !3)
+///                        file: !1, line: 7, type: !2, arg: 2, flags: 7)
 bool LLParser::ParseMDLocalVariable(MDNode *&Result, bool IsDistinct) {
 #define VISIT_MD_FIELDS(OPTIONAL, REQUIRED)                                    \
   REQUIRED(tag, DwarfTagField, );                                              \
@@ -3691,14 +3690,13 @@ bool LLParser::ParseMDLocalVariable(MDNode *&Result, bool IsDistinct) {
   OPTIONAL(line, LineField, );                                                 \
   OPTIONAL(type, MDField, );                                                   \
   OPTIONAL(arg, MDUnsignedField, (0, UINT8_MAX));                              \
-  OPTIONAL(flags, DIFlagField, );                                              \
-  OPTIONAL(inlinedAt, MDField, );
+  OPTIONAL(flags, DIFlagField, );
   PARSE_MD_FIELDS();
 #undef VISIT_MD_FIELDS
 
-  Result = GET_OR_DISTINCT(
-      MDLocalVariable, (Context, tag.Val, scope.Val, name.Val, file.Val,
-                        line.Val, type.Val, arg.Val, flags.Val, inlinedAt.Val));
+  Result = GET_OR_DISTINCT(MDLocalVariable,
+                           (Context, tag.Val, scope.Val, name.Val, file.Val,
+                            line.Val, type.Val, arg.Val, flags.Val));
   return false;
 }