[IRMover] Add comment and fix test case

llvm-svn: 323407

2 files changed, 11 insertions, 1 deletions

diff --git a/llvm/lib/Linker/IRMover.cpp b/llvm/lib/Linker/IRMover.cpp
index f7170e714b9..6863a895cb1 100644
--- a/llvm/lib/Linker/IRMover.cpp
+++ b/llvm/lib/Linker/IRMover.cpp
@@ -95,6 +95,12 @@ void TypeMapTy::addTypeMapping(Type *DstTy, Type *SrcTy) {
     for (StructType *Ty : SpeculativeDstOpaqueTypes)
       DstResolvedOpaqueTypes.erase(Ty);
   } else {
+    // SrcTy and DstTy are recursively ismorphic. We clear names of SrcTy
+    // and all its descendants to lower amount of renaming in LLVM context
+    // Renaming occurs because we load all source modules to the same context
+    // and declaration with existing name gets renamed (i.e Foo -> Foo.42).
+    // As a result we may get several different types in the destination
+    // module, which are in fact the same.
     for (Type *Ty : SpeculativeTypes)
       if (auto *STy = dyn_cast<StructType>(Ty))
         if (STy->hasName())
diff --git a/llvm/test/Linker/type-unique-dst-types.ll b/llvm/test/Linker/type-unique-dst-types.ll
index 1adad49de91..cfcad130e6a 100644
--- a/llvm/test/Linker/type-unique-dst-types.ll
+++ b/llvm/test/Linker/type-unique-dst-types.ll
@@ -1,6 +1,8 @@
 ; RUN: llvm-link %p/type-unique-dst-types.ll \
 ; RUN:           %p/Inputs/type-unique-dst-types2.ll \
-; RUN:           %p/Inputs/type-unique-dst-types3.ll -S -o - | FileCheck %s
+; RUN:           %p/Inputs/type-unique-dst-types3.ll -S -o %t1.ll
+; RUN: cat %t1.ll | FileCheck %s
+; RUN: cat %t1.ll | FileCheck --check-prefix=RENAMED %s
 
 ; This tests the importance of keeping track of which types are part of the
 ; destination module.
@@ -14,6 +16,8 @@
 ; CHECK: @g1 = external global %A
 ; CHECK: @g2 = external global %A
 
+; RENAMED-NOT: A.11
+
 %A = type { %B }
 %B = type { i8 }
 @g3 = external global %A