[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, 8 insertions, 4 deletions

diff --git a/llvm/lib/Analysis/ModuleSummaryAnalysis.cpp b/llvm/lib/Analysis/ModuleSummaryAnalysis.cpp
index 3ad0bab..deda1ee 100644
--- a/llvm/lib/Analysis/ModuleSummaryAnalysis.cpp
+++ b/llvm/lib/Analysis/ModuleSummaryAnalysis.cpp
@@ -635,7 +635,8 @@ static void computeFunctionSummary(
                               HasIndirBranchToBlockAddress || HasIFuncCall;
   GlobalValueSummary::GVFlags Flags(
       F.getLinkage(), F.getVisibility(), NotEligibleForImport,
-      /* Live = */ false, F.isDSOLocal(), F.canBeOmittedFromSymbolTable());
+      /* Live = */ false, F.isDSOLocal(), F.canBeOmittedFromSymbolTable(),
+      GlobalValueSummary::ImportKind::Definition);
   FunctionSummary::FFlags FunFlags{
       F.doesNotAccessMemory(), F.onlyReadsMemory() && !F.doesNotAccessMemory(),
       F.hasFnAttribute(Attribute::NoRecurse), F.returnDoesNotAlias(),
@@ -761,7 +762,8 @@ static void computeVariableSummary(ModuleSummaryIndex &Index,
   bool NonRenamableLocal = isNonRenamableLocal(V);
   GlobalValueSummary::GVFlags Flags(
       V.getLinkage(), V.getVisibility(), NonRenamableLocal,
-      /* Live = */ false, V.isDSOLocal(), V.canBeOmittedFromSymbolTable());
+      /* Live = */ false, V.isDSOLocal(), V.canBeOmittedFromSymbolTable(),
+      GlobalValueSummary::Definition);
 
   VTableFuncList VTableFuncs;
   // If splitting is not enabled, then we compute the summary information
@@ -807,7 +809,8 @@ static void computeAliasSummary(ModuleSummaryIndex &Index, const GlobalAlias &A,
   bool NonRenamableLocal = isNonRenamableLocal(A);
   GlobalValueSummary::GVFlags Flags(
       A.getLinkage(), A.getVisibility(), NonRenamableLocal,
-      /* Live = */ false, A.isDSOLocal(), A.canBeOmittedFromSymbolTable());
+      /* Live = */ false, A.isDSOLocal(), A.canBeOmittedFromSymbolTable(),
+      GlobalValueSummary::Definition);
   auto AS = std::make_unique<AliasSummary>(Flags);
   auto AliaseeVI = Index.getValueInfo(Aliasee->getGUID());
   assert(AliaseeVI && "Alias expects aliasee summary to be available");
@@ -887,7 +890,8 @@ ModuleSummaryIndex llvm::buildModuleSummaryIndex(
               GlobalValue::InternalLinkage, GlobalValue::DefaultVisibility,
               /* NotEligibleToImport = */ true,
               /* Live = */ true,
-              /* Local */ GV->isDSOLocal(), GV->canBeOmittedFromSymbolTable());
+              /* Local */ GV->isDSOLocal(), GV->canBeOmittedFromSymbolTable(),
+              GlobalValueSummary::Definition);
           CantBePromoted.insert(GV->getGUID());
           // Create the appropriate summary type.
           if (Function *F = dyn_cast<Function>(GV)) {