WholeProgramDevirt: When promoting for single-impl devirt, also rename the comdat.

[pcc]

Summary

This is required when targeting COFF, as the comdat name must match
one of the names of the symbols in the comdat.

llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp

bool DevirtModule::trySingleImplDevirt(
   applySingleImplDevirt(SlotInfo, TheFn, IsExported);
   if (!IsExported)
     return false;
 
   // If the only implementation has local linkage, we must promote to external
   // to make it visible to thin LTO objects. We can only get here during the
   // ThinLTO export phase.
   if (TheFn->hasLocalLinkage()) {
+    std::string NewName = (TheFn->getName() + "$merged").str();
+
+    // Since we are renaming the function, any comdats with the same name must
+    // also be renamed. This is required when targeting COFF, as the comdat name
+    // must match one of the names of the symbols in the comdat.
+    if (Comdat *C = TheFn->getComdat()) {
+      if (C->getName() == TheFn->getName()) {
+        Comdat *NewC = M.getOrInsertComdat(NewName);
+        NewC->setSelectionKind(C->getSelectionKind());
+        for (GlobalObject &GO : M.global_objects())
+          if (GO.getComdat() == C)
+            GO.setComdat(NewC);
+      }
+    }
+
     TheFn->setLinkage(GlobalValue::ExternalLinkage);
     TheFn->setVisibility(GlobalValue::HiddenVisibility);
-    TheFn->setName(TheFn->getName() + "$merged");
+    TheFn->setName(NewName);
   }
 
   Res->TheKind = WholeProgramDevirtResolution::SingleImpl;
   Res->SingleImplName = TheFn->getName();
 
   return true;
 }
 

llvm/test/Transforms/WholeProgramDevirt/export-single-impl.ll

 ; SUMMARY-NEXT:         ResByArg:
 ; SUMMARY-NEXT:   typeid3:
 ; SUMMARY-NEXT:     TTRes:
 ; SUMMARY-NEXT:       Kind:            Unsat
 ; SUMMARY-NEXT:       SizeM1BitWidth:  0
 ; SUMMARY-NEXT:     WPDRes:
 ; SUMMARY-NEXT:       0:
 ; SUMMARY-NEXT:         Kind:            SingleImpl
-; SUMMARY-NEXT:         SingleImplName:  vf3
+; SUMMARY-NEXT:         SingleImplName:  'vf3$merged'
 ; SUMMARY-NEXT:         ResByArg:
 ; SUMMARY-NEXT:   typeid4:
 ; SUMMARY-NEXT:     TTRes:
 ; SUMMARY-NEXT:       Kind:            Unsat
 ; SUMMARY-NEXT:       SizeM1BitWidth:  0
 ; SUMMARY-NEXT:     WPDRes:
 ; SUMMARY-NEXT:       0:
 ; SUMMARY-NEXT:         Kind:            SingleImpl
 ; SUMMARY-NEXT:         SingleImplName:  'vf4$merged'
 ; SUMMARY-NEXT:         ResByArg:
 ; SUMMARY-NEXT: WithGlobalValueDeadStripping: false
 ; SUMMARY-NEXT: ...
 
+; CHECK: $"vf4$merged" = comdat largest
+$vf4 = comdat largest
+
 ; CHECK: @vt1 = constant void (i8*)* @vf1
 @vt1 = constant void (i8*)* @vf1, !type !0
 
 ; CHECK: @vt2 = constant void (i8*)* @vf2
 @vt2 = constant void (i8*)* @vf2, !type !1
 
 @vt3 = constant void (i8*)* @vf3, !type !2
 
-; CHECK: @vt4 = constant void (i8*)* @"vf4$merged"
-@vt4 = constant void (i8*)* @vf4, !type !3
+; CHECK: @vt4 = constant void (i8*)* @"vf4$merged", comdat($"vf4$merged")
+@vt4 = constant void (i8*)* @vf4, comdat($vf4), !type !3
 
 @vt5 = constant void (i8*)* @vf5, !type !4
 
 ; CHECK: declare void @vf1(i8*)
 declare void @vf1(i8*)
 
 ; CHECK: define void @vf2(i8*)
 define void @vf2(i8*) {
   ret void
 }
 
-declare void @vf3(i8*)
+; CHECK: define hidden void @"vf3$merged"(i8*) {
+define internal void @vf3(i8*) {
+  ret void
+}
 
-; CHECK: define hidden void @"vf4$merged"
-define internal void @vf4(i8*) {
+; CHECK: define hidden void @"vf4$merged"(i8*) comdat {
+define internal void @vf4(i8*) comdat {
   ret void
 }
 
 declare void @vf5(i8*)
 
 !0 = !{i32 0, !"typeid1"}
 !1 = !{i32 0, !"typeid2"}
 !2 = !{i32 0, !"typeid3"}
 !3 = !{i32 0, !"typeid4"}
 !4 = !{i32 0, !5}
 !5 = distinct !{}