[ms] Emit vtordisp initializers in a deterministic order.

[thakis]

Summary

No effective behavior change, just for cleanliness.

Fixes PR36159.

[thakis]

lib/CodeGen/MicrosoftCXXABI.cpp

1207

(I added the missing & here locally.)

[efriedma]

lib/CodeGen/MicrosoftCXXABI.cpp

1202

Using stable_sort() here, as opposed to sort(), doesn't do anything useful here; VBaseMap is a DenseMap with a pointer key, so the input is in random order anyway.

[thakis]

sort unstably

[rnk]

Thanks for investigating!

lib/CodeGen/MicrosoftCXXABI.cpp

1206

I think we can avoid the sort altogether if we iterate RD->vbases(), which should already be in layout order, and then do lookup into VBaseMap.

[thakis]

rnk comment

[thakis]

lib/CodeGen/MicrosoftCXXABI.cpp

1206

That's way nicer, thanks. Done.

[rnk]

lgtm

lib/CodeGen/MicrosoftCXXABI.cpp

1213

The getVBaseClassOffset call turns around and does the same hashtable lookup we just did. Let's keep the iterator around and say I->second.VBaseOffset.getQuantity().

[thakis]

r326960, thanks!

lib/CodeGen/MicrosoftCXXABI.cpp

void MicrosoftCXXABI::initializeHiddenVirtualInheritanceMembers(
   const ASTRecordLayout &Layout = getContext().getASTRecordLayout(RD);
   typedef ASTRecordLayout::VBaseOffsetsMapTy VBOffsets;
   const VBOffsets &VBaseMap = Layout.getVBaseOffsetsMap();
   CGBuilderTy &Builder = CGF.Builder;
 
   unsigned AS = getThisAddress(CGF).getAddressSpace();
   llvm::Value *Int8This = nullptr;  // Initialize lazily.
 
-  for (VBOffsets::const_iterator I = VBaseMap.begin(), E = VBaseMap.end();
-        I != E; ++I) {
-    if (!I->second.hasVtorDisp())
+  // Emit vtordisps in vbase offset order, to have deterministic output.
+  typedef VBOffsets::value_type VBase;
+  SmallVector<VBase, 4> VBases(VBaseMap.begin(), VBaseMap.end());
+  std::sort(VBases.begin(), VBases.end(), [](const VBase &a, const VBase &b) {
+    return a.second.VBaseOffset < b.second.VBaseOffset;
+  });
+
+  for (const VBase &V : VBases) {
+    if (!V.second.hasVtorDisp())
       continue;
 
     llvm::Value *VBaseOffset =
-        GetVirtualBaseClassOffset(CGF, getThisAddress(CGF), RD, I->first);
+        GetVirtualBaseClassOffset(CGF, getThisAddress(CGF), RD, V.first);
     uint64_t ConstantVBaseOffset =
-        Layout.getVBaseClassOffset(I->first).getQuantity();
+        Layout.getVBaseClassOffset(V.first).getQuantity();
 
     // vtorDisp_for_vbase = vbptr[vbase_idx] - offsetof(RD, vbase).
     llvm::Value *VtorDispValue = Builder.CreateSub(
         VBaseOffset, llvm::ConstantInt::get(CGM.PtrDiffTy, ConstantVBaseOffset),
         "vtordisp.value");
     VtorDispValue = Builder.CreateTruncOrBitCast(VtorDispValue, CGF.Int32Ty);
 
     if (!Int8This)