[ThinLTO] Look through aliases in cache key calculations

[george.burgess.iv]

Summary

We can sometimes get incomplete cache keys (e.g. from not accounting for used type IDs/etc. by an aliasee) when using aliases. This patch aims to fix that.

If you want me to build my own specific test for this, I'm happy to do so. Tweaking this existing test seems to work just as well, though. Please let me know :)

[tejohnson]

lib/LTO/LTO.cpp

189

By skipping the alias here, we don't end up hashing its own live bit. I have a suggestion below.

218

This loop will call AddUsedThings for every global defined in this module, so presumably this already handles both the alias and the base object.

224–231

Presumably this is where we were missing the base object, because we may have the alias in the import list but not its base object (but we will actually import the alias as a copy of the base object). My suggestion would be to check if the summary is an alias here, and if so call AddUsedThings a second time on the base object summary.

[george.burgess.iv]

Addressed feedback

[george.burgess.iv]

Thanks for the feedback!

lib/LTO/LTO.cpp

224–231

SGTM.

The _or_null in my new patch was out of caution rather than actual test failures. Please let me know if I should be able to assume S != nullptr, and I'm happy to drop that. :)

[tejohnson]

LGTM

lib/LTO/LTO.cpp

224–231

I would have thought we should get a non-null S, but the existing code handles it (the early return in AddUsedThings), so it is ok with me to keep the _or_null here.

[george.burgess.iv]

Thanks again! :)

lib/LTO/LTO.cpp

if (CfiFunctionDecls.count(ValueGUID))
       UsedCfiDecls.insert(ValueGUID);
   };
 
   auto AddUsedThings = [&](GlobalValueSummary *GS) {
     if (!GS) return;
     AddUnsigned(GS->isLive());
     for (const ValueInfo &VI : GS->refs()) {
       AddUnsigned(VI.isDSOLocal());
       AddUsedCfiGlobal(VI.getGUID());
     }
     if (auto *GVS = dyn_cast<GlobalVarSummary>(GS))
       AddUnsigned(GVS->isReadOnly());
     if (auto *FS = dyn_cast<FunctionSummary>(GS)) {
       for (auto &TT : FS->type_tests())
         UsedTypeIds.insert(TT);
       for (auto &TT : FS->type_test_assume_vcalls())
         UsedTypeIds.insert(TT.GUID);
#endif
 
   // Include the hash for the linkage type to reflect internalization and weak
   // resolution, and collect any used type identifier resolutions.
   for (auto &GS : DefinedGlobals) {
     GlobalValue::LinkageTypes Linkage = GS.second->linkage();
     Hasher.update(
         ArrayRef<uint8_t>((const uint8_t *)&Linkage, sizeof(Linkage)));
     AddUsedCfiGlobal(GS.first);
     AddUsedThings(GS.second);
   }
 
   // Imported functions may introduce new uses of type identifier resolutions,
   // so we need to collect their used resolutions as well.
   for (auto &ImpM : ImportList)
-    for (auto &ImpF : ImpM.second)
-      AddUsedThings(Index.findSummaryInModule(ImpF, ImpM.first()));
+    for (auto &ImpF : ImpM.second) {
+      GlobalValueSummary *S = Index.findSummaryInModule(ImpF, ImpM.first());
+      AddUsedThings(S);
+      // If this is an alias, we also care about any types/etc. that the aliasee
+      // may reference.
+      if (auto *AS = dyn_cast_or_null<AliasSummary>(S))
+        AddUsedThings(AS->getBaseObject());
+    }
 
   auto AddTypeIdSummary = [&](StringRef TId, const TypeIdSummary &S) {
     AddString(TId);
 
     AddUnsigned(S.TTRes.TheKind);
     AddUnsigned(S.TTRes.SizeM1BitWidth);
 
     AddUint64(S.TTRes.AlignLog2);

test/ThinLTO/X86/cache-typeid-resolutions.ll

 ; RUN: opt -module-hash -module-summary %s -o %t.bc
 ; RUN: opt -module-hash -module-summary %S/Inputs/cache-typeid-resolutions-import.ll -o %t-import.bc
 
 ; RUN: llvm-as -o %t1.bc %S/Inputs/cache-typeid-resolutions1.ll
 ; RUN: llvm-as -o %t2.bc %S/Inputs/cache-typeid-resolutions2.ll
 ; RUN: llvm-as -o %t3.bc %S/Inputs/cache-typeid-resolutions3.ll
 
 ; Two resolutions for typeid1: Unsat, Single
 ; where both t and t-import are sensitive to typeid1's resolution
 ; so 4 distinct objects in total.
 ; RUN: rm -rf %t.cache
-; RUN: llvm-lto2 run -o %t.o %t.bc %t-import.bc -cache-dir %t.cache -r=%t.bc,f1,plx -r=%t.bc,f2,plx -r=%t-import.bc,importf1,plx -r=%t-import.bc,f1,lx -r=%t-import.bc,importf2,plx -r=%t-import.bc,f2,lx
-; RUN: llvm-lto2 run -o %t.o %t.bc %t-import.bc %t1.bc -cache-dir %t.cache -r=%t.bc,f1,plx -r=%t.bc,f2,plx -r=%t-import.bc,importf1,plx -r=%t-import.bc,f1,lx -r=%t-import.bc,importf2,plx -r=%t-import.bc,f2,lx -r=%t1.bc,vt1,plx
+; RUN: llvm-lto2 run -o %t.o %t.bc %t-import.bc -cache-dir %t.cache -r=%t.bc,f1,plx -r=%t.bc,f1_actual,plx -r=%t.bc,f2,plx -r=%t-import.bc,importf1,plx -r=%t-import.bc,f1,lx -r=%t-import.bc,importf2,plx -r=%t-import.bc,f2,lx
+; RUN: llvm-lto2 run -o %t.o %t.bc %t-import.bc %t1.bc -cache-dir %t.cache -r=%t.bc,f1,plx -r=%t.bc,f1_actual,plx -r=%t.bc,f2,plx -r=%t-import.bc,importf1,plx -r=%t-import.bc,f1,lx -r=%t-import.bc,importf2,plx -r=%t-import.bc,f2,lx -r=%t1.bc,vt1,plx
 ; RUN: ls %t.cache | count 4
 
 ; Three resolutions for typeid2: Indir, SingleImpl, UniqueRetVal
 ; where both t and t-import are sensitive to typeid2's resolution
 ; so 6 distinct objects in total.
 ; RUN: rm -rf %t.cache
-; RUN: llvm-lto2 run -o %t.o %t.bc %t-import.bc -cache-dir %t.cache -r=%t.bc,f1,plx -r=%t.bc,f2,plx -r=%t-import.bc,importf1,plx -r=%t-import.bc,f1,lx -r=%t-import.bc,importf2,plx -r=%t-import.bc,f2,lx
-; RUN: llvm-lto2 run -o %t.o %t.bc %t-import.bc %t2.bc -cache-dir %t.cache -r=%t.bc,f1,plx -r=%t.bc,f2,plx -r=%t2.bc,vt2,plx -r=%t-import.bc,importf1,plx -r=%t-import.bc,f1,lx -r=%t-import.bc,importf2,plx -r=%t-import.bc,f2,lx
-; RUN: llvm-lto2 run -o %t.o %t.bc %t-import.bc %t3.bc -cache-dir %t.cache -r=%t.bc,f1,plx -r=%t.bc,f2,plx -r=%t3.bc,vt2a,plx -r=%t3.bc,vt2b,plx -r=%t-import.bc,importf1,plx -r=%t-import.bc,f1,lx -r=%t-import.bc,importf2,plx -r=%t-import.bc,f2,lx
+; RUN: llvm-lto2 run -o %t.o %t.bc %t-import.bc -cache-dir %t.cache -r=%t.bc,f1,plx -r=%t.bc,f2,plx -r=%t.bc,f1_actual,plx -r=%t-import.bc,importf1,plx -r=%t-import.bc,f1,lx -r=%t-import.bc,importf2,plx -r=%t-import.bc,f2,lx
+; RUN: llvm-lto2 run -o %t.o %t.bc %t-import.bc %t2.bc -cache-dir %t.cache -r=%t.bc,f1,plx -r=%t.bc,f2,plx -r=%t.bc,f1_actual,plx -r=%t2.bc,vt2,plx -r=%t-import.bc,importf1,plx -r=%t-import.bc,f1,lx -r=%t-import.bc,importf2,plx -r=%t-import.bc,f2,lx
+; RUN: llvm-lto2 run -o %t.o %t.bc %t-import.bc %t3.bc -cache-dir %t.cache -r=%t.bc,f1,plx -r=%t.bc,f2,plx -r=%t.bc,f1_actual,plx -r=%t3.bc,vt2a,plx -r=%t3.bc,vt2b,plx -r=%t-import.bc,importf1,plx -r=%t-import.bc,f1,lx -r=%t-import.bc,importf2,plx -r=%t-import.bc,f2,lx
 ; RUN: ls %t.cache | count 6
 
 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"
 
-define i1 @f1(i8* %p) {
+@f1 = alias i1(i8*), i1 (i8*)* @f1_actual
+
+define i1 @f1_actual(i8* %p) {
   %x = call i1 @llvm.type.test(i8* %p, metadata !"typeid1")
   ret i1 %x
 }
 
 define i1 @f2(i8* %obj) {
   %vtableptr = bitcast i8* %obj to [3 x i8*]**
   %vtable = load [3 x i8*]*, [3 x i8*]** %vtableptr
   %vtablei8 = bitcast [3 x i8*]* %vtable to i8*