[ThinLTO] Allow importing of functions with var args

[tejohnson]

Summary

Follow up to D54270, which allowed importing of var args functions
unless they called va_start. As pointed out in the post-commit comments
on that patch, the inliner can handle functions that call va_start in
certain situations as well. Go ahead and enable importing of all var
args functions. Measurements on a large binary show that this increases
imports and binary size by an insignificant amount.

[tejohnson]

ping

[davidxl]

lgtm

lib/Analysis/ModuleSummaryAnalysis.cpp

static void computeFunctionSummary(
   ICallPromotionAnalysis ICallAnalysis;
   SmallPtrSet<const User *, 8> Visited;
 
   // Add personality function, prefix data and prologue data to function's ref
   // list.
   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);
       if (!CS)
         continue;
 
       const auto *CI = dyn_cast<CallInst>(&I);
       // Since we don't know exactly which local values are referenced in inline
static void computeFunctionSummary(
   bool NotEligibleForImport =
       NonRenamableLocal || HasInlineAsmMaybeReferencingInternal;
   GlobalValueSummary::GVFlags Flags(F.getLinkage(), NotEligibleForImport,
                                     /* Live = */ false, F.isDSOLocal());
   FunctionSummary::FFlags FunFlags{
       F.hasFnAttribute(Attribute::ReadNone),
       F.hasFnAttribute(Attribute::ReadOnly),
       F.hasFnAttribute(Attribute::NoRecurse), F.returnDoesNotAlias(),
-      // Inliner doesn't handle variadic functions with va_start calls.
       // FIXME: refactor this to use the same code that inliner is using.
-      InitsVarArgs ||
-          // Don't try to import functions with noinline attribute.
-          F.getAttributes().hasFnAttribute(Attribute::NoInline)};
   auto FuncSummary = llvm::make_unique<FunctionSummary>(
       Flags, NumInsts, FunFlags, RefEdges.takeVector(),
       CallGraphEdges.takeVector(), TypeTests.takeVector(),
       TypeTestAssumeVCalls.takeVector(), TypeCheckedLoadVCalls.takeVector(),
       TypeTestAssumeConstVCalls.takeVector(),
       TypeCheckedLoadConstVCalls.takeVector());
   if (NonRenamableLocal)
     CantBePromoted.insert(F.getGUID());

test/Bitcode/thinlto-function-summary.ll

 ; BC-NEXT: <FUNCTION op0=54 op1=13
 ; "f"
 ; BC-NEXT: <ALIAS op0=67 op1=1
 ; BC: <GLOBALVAL_SUMMARY_BLOCK
 ; BC-NEXT: <VERSION
 ; BC-NEXT: <PERMODULE {{.*}} op0=1 op1=0
 ; BC-NEXT: <PERMODULE {{.*}} op0=2 op1=0
 ; BC-NEXT: <PERMODULE {{.*}} op0=3 op1=7
-; Summary for @variadic has flags (op3) = 16 since non-inlinable owing to
-; va_start call.
-; flag is set due to va_start call.
-; BC-NEXT: <PERMODULE {{.*}} op0=4 op1=0 op2=4 op3=16
+; BC-NEXT: <PERMODULE {{.*}} op0=4 op1=0 op2=4 op3=0
 ; BC-NEXT: <ALIAS {{.*}} op0=6 op1=0 op2=3
 ; BC-NEXT: </GLOBALVAL_SUMMARY_BLOCK
 ; BC: <STRTAB_BLOCK
 ; BC-NEXT: blob data = 'hfoobaranon.{{................................}}.0variadicllvm.va_startf{{.*}}'
 
 
 ; RUN: opt -name-anon-globals -module-summary < %s | llvm-dis | FileCheck %s
 ; Check that this round-trips correctly.

test/Transforms/FunctionImport/funcimport.ll

 ; INSTLIM5-DAG: declare hidden void @funcwithpersonality.llvm.{{.*}}()
 
 ; We can import variadic functions without a va_start, since the inliner
 ; can handle them.
 ; INSTLIMDEF-DAG: Import variadic_no_va_start
 ; CHECK-DAG: define available_externally void @variadic_no_va_start(...) !thinlto_src_module !0 {
 declare void @variadic_no_va_start(...)
 
-; We shouldn't import variadic functions without a va_start, since the inliner
-; cannot handle them.
-; CHECK-DAG: declare void @variadic_va_start(...)
+; We can import variadic functions with a va_start, since the inliner
+; can sometimes handle them.
+; CHECK-DAG: define available_externally void @variadic_va_start(...)
 declare void @variadic_va_start(...)
 
 ; INSTLIMDEF-DAG: Import globalfunc2
-; INSTLIMDEF-DAG: 14 function-import - Number of functions imported
+; INSTLIMDEF-DAG: 15 function-import - Number of functions imported
 ; INSTLIMDEF-DAG: 4 function-import - Number of global variables imported
 
 ; CHECK-DAG: !0 = !{!"{{.*}}/Inputs/funcimport.ll"}
 
 ; The actual GUID values will depend on path to test.
 ; GUID-DAG: GUID {{.*}} is weakalias
 ; GUID-DAG: GUID {{.*}} is referenceglobals
 ; GUID-DAG: GUID {{.*}} is weakfunc

 ; GUID-DAG: GUID {{.*}} is analias
 ; GUID-DAG: GUID {{.*}} is globalvar
 ; GUID-DAG: GUID {{.*}} is referencecommon
 ; GUID-DAG: GUID {{.*}} is linkoncealias
 ; GUID-DAG: GUID {{.*}} is callfuncptr
 ; GUID-DAG: GUID {{.*}} is linkoncefunc
 
 ; DUMP:       Module [[M1:.*]] imports from 1 module
-; DUMP-NEXT:  14 functions imported from [[M2:.*]]
+; DUMP-NEXT:  15 functions imported from [[M2:.*]]
 ; DUMP-NEXT:  4 vars imported from [[M2]]
-; DUMP:       Imported 14 functions for Module [[M1]]
+; DUMP:       Imported 15 functions for Module [[M1]]
 ; DUMP-NEXT:  Imported 4 global variables for Module [[M1]]