[ThinLTO] Handle variable with twice promoted name (Rust)

llvm/include/llvm/IR/ModuleSummaryIndex.h

@@ -1239,9 +1239,11 @@ class ModuleSummaryIndex {
   }
 
   /// Helper to obtain the unpromoted name for a global value (or the original
-  /// name if not promoted).
+  /// name if not promoted). Split off the rightmost ".llvm.${hash}" suffix,
+  /// because it is possible in certain clients (not clang at the moment) for
+  /// two rounds of ThinLTO optimization and therefore promotion to occur.
   static StringRef getOriginalNameBeforePromote(StringRef Name) {
-    std::pair<StringRef, StringRef> Pair = Name.split(".llvm.");
+    std::pair<StringRef, StringRef> Pair = Name.rsplit(".llvm.");
     return Pair.first;
   }
 

llvm/test/ThinLTO/X86/Inputs/thinlto-internalize-doublepromoted.ll

@@ -0,0 +1,10 @@
+target datalayout = "e-m:o-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.15.0"
+
+define i32 @main() {
+entry:
+  call void @foo.llvm.123()
+  ret i32 0
+}
+
+declare void @foo.llvm.123()

llvm/test/ThinLTO/X86/thinlto-internalize-doublepromoted.ll

@@ -0,0 +1,33 @@
+; Test to ensure that we can internalize values produced from two rounds
+; of ThinLTO promotion, so they end up with two ".llvm.${hash}" suffixes.
+; Only the second should be stripped when consulting the index to locate the
+; summary.
+;
+; Note that this cannot happen currently via clang, but in other use cases such
+; as the Rust compiler which does a first round of ThinLTO on library code,
+; producing bitcode, and a second round on the final binary.
+;
+; In this case we assume a prior round of ThinLTO has promoted @foo, and
+; subsequent optimization created an internal switch table expansion variable
+; that is internal and contains the promoted name of the enclosing function.
+; This variable will be promoted in the second round of ThinLTO if @foo is
+; imported again.
+
+; RUN: opt -module-summary -o %t.bc %s
+; RUN: opt -module-summary -o %t-main.bc %S/Inputs/thinlto-internalize-doublepromoted.ll
+; RUN: llvm-lto -thinlto-action=thinlink %t.bc %t-main.bc -o %t-index.bc
+; RUN: llvm-lto -thinlto-action=internalize -exported-symbol=main -thinlto-index %t-index.bc %t.bc -o %t.internalize.bc
+; RUN: llvm-dis %t.internalize.bc -o - | FileCheck %s
+
+target datalayout = "e-m:o-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.15.0"
+
+; CHECK: @switch.table.foo.llvm.123.llvm.0 = hidden unnamed_addr constant
+@switch.table.foo.llvm.123 = private unnamed_addr constant [10 x i8] c"\00\01\02\03\00\00\00\00\00\09", align 1
+
+; CHECK: define hidden void @foo.llvm.123()
+define hidden void @foo.llvm.123() {
+  %1 = getelementptr inbounds [10 x i8], [10 x i8]* @switch.table.foo.llvm.123, i64 0, i64 0
+  store i8 1, i8* %1, align 8
+  ret void
+}