[ThinLTO] Update handling of vararg functions to match inliner

Summary:
Previously we marked all vararg functions as non-inlinable in the
function summary, which prevented their importing. However, the
corresponding inliner restriction was loosened in r321940/r342675
to only apply to functions calling va_start. Adjust the summary
flag computation to match.

Reviewers: davidxl

Subscribers: mehdi_amini, inglorion, eraman, steven_wu, dexonsmith, llvm-commits

Differential Revision: https://reviews.llvm.org/D54270

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@346883 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Analysis/ModuleSummaryAnalysis.cpp

@@ -246,10 +246,15 @@ static void computeFunctionSummary(
   findRefEdges(Index, &F, RefEdges, Visited);
 
   bool HasInlineAsmMaybeReferencingInternal = false;
+  bool InitsVarArgs = false;
   for (const BasicBlock &BB : F)
     for (const Instruction &I : BB) {
       if (isa<DbgInfoIntrinsic>(I))
         continue;
+      if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(&I)) {
+        if (II->getIntrinsicID() == Intrinsic::vastart)
+          InitsVarArgs = true;
+      }
       ++NumInsts;
       findRefEdges(Index, &I, RefEdges, Visited);
       auto CS = ImmutableCallSite(&I);
@@ -357,9 +362,9 @@ static void computeFunctionSummary(
       F.hasFnAttribute(Attribute::ReadNone),
       F.hasFnAttribute(Attribute::ReadOnly),
       F.hasFnAttribute(Attribute::NoRecurse), F.returnDoesNotAlias(),
-      // Inliner doesn't handle variadic functions.
+      // Inliner doesn't handle variadic functions with va_start calls.
       // FIXME: refactor this to use the same code that inliner is using.
-      F.isVarArg() ||
+      InitsVarArgs ||
           // Don't try to import functions with noinline attribute.
           F.getAttributes().hasFnAttribute(Attribute::NoInline)};
   auto FuncSummary = llvm::make_unique<FunctionSummary>(