llvm-link option and test for recent metadata mapping bug

Summary:
Add a -preserve-modules option to llvm-link that simulates LTO
clients that don't destroy modules as they are linked. This enables
reproduction of a recent bug introduced by a metadata linking change
that was only caught when the modules weren't destroyed before
writing bitcode (LTO on Windows).

See http://llvm.org/viewvc/llvm-project?view=revision&revision=253170
for more details on the original bug and the fix.

Confirmed the new test added here reproduces the failure using the new
option when I suppress the fix.

Reviewers: pcc

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D14818

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@253740 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 13 insertions, 0 deletions

diff --git a/tools/llvm-link/llvm-link.cpp b/tools/llvm-link/llvm-link.cpp
index c539f75702b..ada55c93a6e 100644
--- a/tools/llvm-link/llvm-link.cpp
+++ b/tools/llvm-link/llvm-link.cpp
@@ -89,6 +89,10 @@ static cl::opt<bool>
 SuppressWarnings("suppress-warnings", cl::desc("Suppress all linking warnings"),
                  cl::init(false));
 
+static cl::opt<bool>
+    PreserveModules("preserve-modules",
+                    cl::desc("Preserve linked modules for testing"));
+
 static cl::opt<bool> PreserveBitcodeUseListOrder(
     "preserve-bc-uselistorder",
     cl::desc("Preserve use-list order when writing LLVM bitcode."),
@@ -259,6 +263,15 @@ static bool linkFiles(const char *argv0, LLVMContext &Context, Linker &L,
       return false;
     // All linker flags apply to linking of subsequent files.
     ApplicableFlags = Flags;
+
+    // If requested for testing, preserve modules by releasing them from
+    // the unique_ptr before the are freed. This can help catch any
+    // cross-module references from e.g. unneeded metadata references
+    // that aren't properly set to null but instead mapped to the source
+    // module version. The bitcode writer will assert if it finds any such
+    // cross-module references.
+    if (PreserveModules)
+      M.release();
   }
 
   return true;