[ThinLTO] Add option to dump per-module summary dot graph

Summary:
I found that there currently isn't a way to invoke exportToDot from
the command line for a per-module summary index, and therefore no
testing of that case. Add an internal option and use it to test dumping
of per module summary indexes.

In particular, I am looking at fixing the limitation that causes the
aliasee GUID in the per-module summary to be 0, and want to be able to
test that change.

Reviewers: evgeny777

Subscribers: mehdi_amini, inglorion, eraman, steven_wu, dexonsmith, llvm-commits

Differential Revision: https://reviews.llvm.org/D57206

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@352441 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Analysis/ModuleSummaryAnalysis.cpp

@@ -70,6 +70,11 @@ cl::opt<FunctionSummary::ForceSummaryHotnessType, true> FSEC(
                           "all-non-critical", "All non-critical edges."),
                clEnumValN(FunctionSummary::FSHT_All, "all", "All edges.")));
 
+cl::opt<std::string> ModuleSummaryDotFile(
+    "module-summary-dot-file", cl::init(""), cl::Hidden,
+    cl::value_desc("filename"),
+    cl::desc("File to emit dot graph of new summary into."));
+
 // Walk through the operands of a given User via worklist iteration and populate
 // the set of GlobalValue references encountered. Invoked either on an
 // Instruction or a GlobalVariable (which walks its initializer).
@@ -625,6 +630,15 @@ ModuleSummaryIndex llvm::buildModuleSummaryIndex(
     }
   }
 
+  if (!ModuleSummaryDotFile.empty()) {
+    std::error_code EC;
+    raw_fd_ostream OSDot(ModuleSummaryDotFile, EC, sys::fs::OpenFlags::F_None);
+    if (EC)
+      report_fatal_error(Twine("Failed to open dot file ") +
+                         ModuleSummaryDotFile + ": " + EC.message() + "\n");
+    Index.exportToDot(OSDot);
+  }
+
   return Index;
 }