[ThinLTO]Record import type in GlobalValueSummary::GVFlags (#87597)

The motivating use case is to support import the function declaration
across modules to construct call graph edges for indirect calls [1]
when importing the function definition costs too much compile time
(e.g., the function is too large has no `noinline` attribute).
1. Currently, when the compiled IR module doesn't have a function
definition but its postlink combined summary contains the function
summary or a global alias summary with this function as aliasee, the
function definition will be imported from source module by IRMover. The
implementation is in FunctionImporter::importFunctions [2]
2. In order for FunctionImporter to import a declaration of a function,
both function summary and alias summary need to carry the def / decl
state. Specifically, all existing summary fields doesn't differ across
import modules, but the def / decl state of is decided by
`<ImportModule, Function>`.

This change encodes the def/decl state in `GlobalValueSummary::GVFlags`.

In the subsequent changes
1. The indexing step `computeImportForModule` [3]
will compute the set of definitions and the set of declarations for each
module, and passing on the information to bitcode writer.
2. Bitcode writer will look up the def/decl state and sets the state
when it writes out the flag value. This is demonstrated in
https://github.com/llvm/llvm-project/pull/87600
3. Function importer will read the def/decl state when reading the
combined summary to figure out two sets of global values, and IRMover
will be updated to import the declaration (aka linkGlobalValuePrototype [4])
into the destination module.

- The next change is https://github.com/llvm/llvm-project/pull/87600

[1] mentioned in rfc https://discourse.llvm.org/t/rfc-for-better-call-graph-sort-build-a-more-complete-call-graph-by-adding-more-indirect-call-edges/74029#support-cross-module-function-declaration-import-5
[2] https://github.com/llvm/llvm-project/blob/3b337242ee165554f0017b00671381ec5b1ba855/llvm/lib/Transforms/IPO/FunctionImport.cpp#L1608-L1764
[3] https://github.com/llvm/llvm-project/blob/3b337242ee165554f0017b00671381ec5b1ba855/llvm/lib/Transforms/IPO/FunctionImport.cpp#L856
[4] https://github.com/llvm/llvm-project/blob/3b337242ee165554f0017b00671381ec5b1ba855/llvm/lib/Linker/IRMover.cpp#L605

1 files changed, 30 insertions, 3 deletions

diff --git a/llvm/lib/AsmParser/LLParser.cpp b/llvm/lib/AsmParser/LLParser.cpp
index f546e05..6310412 100644
--- a/llvm/lib/AsmParser/LLParser.cpp
+++ b/llvm/lib/AsmParser/LLParser.cpp
@@ -2083,6 +2083,20 @@ void LLParser::parseOptionalVisibility(unsigned &Res) {
   Lex.Lex();
 }
 
+bool LLParser::parseOptionalImportType(lltok::Kind Kind,
+                                       GlobalValueSummary::ImportKind &Res) {
+  switch (Kind) {
+  default:
+    return tokError("unknown import kind. Expect definition or declaration.");
+  case lltok::kw_definition:
+    Res = GlobalValueSummary::Definition;
+    return false;
+  case lltok::kw_declaration:
+    Res = GlobalValueSummary::Declaration;
+    return false;
+  }
+}
+
 /// parseOptionalDLLStorageClass
 ///   ::= /*empty*/
 ///   ::= 'dllimport'
@@ -9230,7 +9244,8 @@ bool LLParser::parseFunctionSummary(std::string Name, GlobalValue::GUID GUID,
   GlobalValueSummary::GVFlags GVFlags = GlobalValueSummary::GVFlags(
       GlobalValue::ExternalLinkage, GlobalValue::DefaultVisibility,
       /*NotEligibleToImport=*/false,
-      /*Live=*/false, /*IsLocal=*/false, /*CanAutoHide=*/false);
+      /*Live=*/false, /*IsLocal=*/false, /*CanAutoHide=*/false,
+      GlobalValueSummary::Definition);
   unsigned InstCount;
   std::vector<FunctionSummary::EdgeTy> Calls;
   FunctionSummary::TypeIdInfo TypeIdInfo;
@@ -9317,7 +9332,8 @@ bool LLParser::parseVariableSummary(std::string Name, GlobalValue::GUID GUID,
   GlobalValueSummary::GVFlags GVFlags = GlobalValueSummary::GVFlags(
       GlobalValue::ExternalLinkage, GlobalValue::DefaultVisibility,
       /*NotEligibleToImport=*/false,
-      /*Live=*/false, /*IsLocal=*/false, /*CanAutoHide=*/false);
+      /*Live=*/false, /*IsLocal=*/false, /*CanAutoHide=*/false,
+      GlobalValueSummary::Definition);
   GlobalVarSummary::GVarFlags GVarFlags(/*ReadOnly*/ false,
                                         /* WriteOnly */ false,
                                         /* Constant */ false,
@@ -9375,7 +9391,8 @@ bool LLParser::parseAliasSummary(std::string Name, GlobalValue::GUID GUID,
   GlobalValueSummary::GVFlags GVFlags = GlobalValueSummary::GVFlags(
       GlobalValue::ExternalLinkage, GlobalValue::DefaultVisibility,
       /*NotEligibleToImport=*/false,
-      /*Live=*/false, /*IsLocal=*/false, /*CanAutoHide=*/false);
+      /*Live=*/false, /*IsLocal=*/false, /*CanAutoHide=*/false,
+      GlobalValueSummary::Definition);
   if (parseToken(lltok::colon, "expected ':' here") ||
       parseToken(lltok::lparen, "expected '(' here") ||
       parseModuleReference(ModulePath) ||
@@ -10161,6 +10178,16 @@ bool LLParser::parseGVFlags(GlobalValueSummary::GVFlags &GVFlags) {
         return true;
       GVFlags.CanAutoHide = Flag;
       break;
+    case lltok::kw_importType:
+      Lex.Lex();
+      if (parseToken(lltok::colon, "expected ':'"))
+        return true;
+      GlobalValueSummary::ImportKind IK;
+      if (parseOptionalImportType(Lex.getKind(), IK))
+        return true;
+      GVFlags.ImportType = static_cast<unsigned>(IK);
+      Lex.Lex();
+      break;
     default:
       return error(Lex.getLoc(), "expected gv flag type");
     }